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7fe2cad0607e6a71d3913bab985d453b61e23b1bacfe11831104c97dae50399f
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2026-01-01T00:00:00-05:00
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Antarctic TianMu Staring Observation Project I: Overview and Implementation of the Prototype Telescope
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arXiv:2512.24067v1 Announce Type: new Abstract: Wide-field rapid sky surveys serve as critical observational methods for time-domain astronomical research. The Antarctic region, with several months of continuous dark nights annually, is an ideal site for time-domain astronomical observations. The Antarctic TianMu Staring Observation Project aims to deploy a fleet of small telescopes, adopting an array observation model to conduct time-domain optical observations in Antarctica, featuring wide-sky coverage, high-cadence sampling, long-period staring, and simultaneous multi-band measurements. Considering the severe challenges optical telescopes face in Antarctica, including extremely low temperatures, unattended operation, and limited power supply and network transmission, we have designed and developed the Antarctic TianMu prototype telescope based on drift-scan charge-coupled device technology. In October 2022, our prototype (with an aperture of 18 cm), named AT-Proto was transported to Zhongshan Station in Antarctica aboard China's 39th Antarctic Research Expedition. It has since operated stably and reliably in the frigid environment for over two years, demonstrating the significant advantages of this technology in polar astronomical observations. The experimental observation results of AT-Proto provide a solid foundation for the subsequent construction of a time-domain astronomy observation array in Antarctica.
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https://arxiv.org/abs/2512.24067
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Academic Papers
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15c520a9560c539326e1ed7eae8489ea9e7951624ae364abc7f300a200c5798d
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2026-01-01T00:00:00-05:00
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Antarctic TianMu Staring Observation Project II: Data reduction and preliminary results
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arXiv:2512.24068v1 Announce Type: new Abstract: The Antarctic TianMu Staring Observation Program is a time-domain optical sky survey project carried out in Antarctica, capable of large sky coverage, high-cadence sampling, and long-period staring. It utilizes the exceptional observing conditions in Antarctica to conduct high-cadence time-domain sky surveys. At present, we have successfully developed an 18-cm aperture Antarctic TianMu prototype, which has been deployed at Zhongshan Station in Antarctica for two consecutive years of trouble-free observations, during which more than 300,000 original images were obtained. This paper systematically outlines the commissioning data of the prototype telescope in 2023, the primary data processing pipeline, and the preliminary data products. The core pipeline encompasses four key stages: Data preprocessing, instrumental effect correction, astrometric solution, and full-field stellar photometry. Here, we release the 2023 data products, which specifically include reduced image data and a photometric catalog, for which, preliminary analyses demonstrate robust performance. Using Gaia Data Release 3 as a reference catalog, the astrometric precision, quantified by the root mean square of positional errors, is determined to be better than approximately 2 arcseconds, validating the observational capabilities of the system. For a 30-second exposure, the detection limit in the G-band is achieved at 15.00~mag, with a detection threshold of 1.5~$\sigma$. The photometric errors are below 0.1~mag for the majority of stars brighter than 14.00~mag. Furthermore, it improves significantly, reaching better than 0.01~mag for most stars brighter than 11.00~mag and 12.00~mag when employing the adaptive aperture photometry and point spread function photometry methods, respectively.
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https://arxiv.org/abs/2512.24068
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Academic Papers
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1a569759ff4a21e857ccf7f39f9fced2398c384168641935915b4914d627a58a
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2026-01-01T00:00:00-05:00
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SSC Radiation in the ICMART Model: Spectral Simulations and Application to the Record-Breaking GRB 221009A
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arXiv:2512.24085v1 Announce Type: new Abstract: This paper presents simulations of the synchrotron self-Compton (SSC) spectrum within the Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model. We investigate how key parameters like the magnetization $\sigma_0$ shape the broadband spectral energy distribution by regulating the electron distribution and magnetic field strength. The overall spectrum typically comprises two components: synchrotron radiation peaking at $E_{\rm p}$ with a low-energy spectral index $\alpha$ between -1 and -1.5, and an SSC component peaking at $E_{\rm ssc}$. At high energies, Klein-Nishina suppression causes an exponential cutoff. The flux ratio Y between these components is critical: when Y is small, the SSC peak can be suppressed. Spectral features of the synchrotron component reveal the underlying physical conditions: harder spectra with $\alpha\sim-1$ indicate a large Y parameter and strong KN suppression. We find a positive correlation between Y and $\sigma_0$, contrasting with internal shock model predictions. Applied to GRB 221009A, our model suggests $\sigma_0\leq20$ can reproduce the MeV-TeV observations. This study underscores the value of combined MeV-TeV observations in probing GRB emission mechanisms.
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https://arxiv.org/abs/2512.24085
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Academic Papers
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26c97aaf01172bd8d1b4098e7b3c30aecf0de9e3788bc8583d78891fd5bcfb43
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2026-01-01T00:00:00-05:00
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photoD with Rubin's Data Preview 1: first stellar photometric distances and deficit of faint blue stars. Stellar distances with Rubin's DP1
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arXiv:2512.24109v1 Announce Type: new Abstract: Aims: We investigate the utility of Rubin's Data Preview 1 for estimating stellar number density profile in the Milky Way halo. Methods: Stellar broad-band near-UV to near-IR $ugrizy$ photometry released in Rubin's Data Preview 1 is used to estimate distance and metallicity for blue main sequence stars brighter than $r=24$ in three $\sim$1.1. sq.~deg. fields at southern Galactic latitudes. Results: Compared to TRILEGAL simulations of the Galaxy's stellar content by (Dal Tio, 2022), we find a significant deficit of blue main sequence turn-off stars with $22 < r < 24$. We interpret this discrepancy as a signature of a much steeper halo number density profile at galactocentric distances $10-50$ kpc than the cannonical $\sim1/r^3$ profile assumed in TRILEGAL simulations. Conclusions: This interpretation is consistent with earlier suggestions based on observations of more luminous, but much less numerous, evolved stellar populations, and a few pencil beam surveys of blue main sequence stars in the northern sky. These results bode well for the future Galactic halo exploration with Rubin's Legacy Survey of Space and Time.
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https://arxiv.org/abs/2512.24109
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Academic Papers
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34373ebfce3de00e455f31830c573399ab52358999612ef7e2cdfdc711bce709
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2026-01-01T00:00:00-05:00
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Evolution of Accretion Properties in Mrk 1040 using long-term X-ray Observations
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arXiv:2512.24141v1 Announce Type: new Abstract: We present a comprehensive long-term, multi-epoch spectral and timing study of the Seyfert 1 Active Galactic Nucleus (AGN) Mrk~1040, utilizing X-ray observations spanning from 2009 to 2024 ($\sim$15 years). The source exhibits pronounced spectral and temporal variability, indicative of transitions between different accretion regimes in the vicinity of the central supermassive black hole. The earlier reported soft excess is re-examined within a uniform, physically motivated multi-epoch framework. We confirm the presence of this soft excess in the 2009 observation, where it is well described by a warm, extended Comptonizing corona with $kT_{\rm e,warm} \sim 0.26$~keV and a radial extent of $R_{\rm warm} \sim 30~r_g$. In subsequent epochs, the soft excess is not statistically significant, possibly due to a combination of enhanced ionized absorption, intrinsic weakening of the warm Comptonizing region, or partial truncation of the inner disc. A strong correlation between the soft and hard X-ray fluxes suggests a common physical origin for both components, likely within a multi-layered Comptonizing structure that evolved into a compact and thermally stable corona after 2013. The observed spectral variability, together with changes in the Fe~K$\alpha$ line strength, reflects the evolving coronal geometry and accretion flow dynamics. Variations in the intrinsic column density ($N_H$) further indicate that Mrk~1040 is embedded within a clumpy, dynamically variable absorber responding to changes in the accretion rate. Using the TCAF model, we estimate the black hole mass as $M_{\rm BH} = (4.50 \pm 1.62) \times 10^7~M_\odot$, consistent with previous estimates.
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https://arxiv.org/abs/2512.24141
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Academic Papers
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d0a1fac10160f0539ea8d65af676a961a08a7d6fcd1c5802712df1fc3ba19943
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2026-01-01T00:00:00-05:00
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A Seyfert galaxy as a hidden counterpart to a neutrino-associated blazar
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arXiv:2512.24178v1 Announce Type: new Abstract: The origin and production mechanisms of high-energy astrophysical neutrinos remain open questions in multimessenger astronomy. Previous studies have hinted at a possible linear correlation between the hard X-ray and high-energy neutrino emission in active galactic nuclei. New \textit{NuSTAR} observations, first presented here, reveal that blazar PKS 1424+240, located within a prominent IceCube neutrino hotspot, is far fainter in hard X-rays than expected from this trend. Motivated by this apparent ambiguity, we identify the nearby Seyfert galaxy NGC 5610, also coincident with the hotspot, whose unabsorbed hard X-ray flux exceeds that of PKS 1424+240 by about an order of magnitude. When the local IceCube neutrino flux is apportioned between the two AGN in proportion to their hard X-ray emission, both align with the previously suggested X-ray-neutrino correlation. This suggests that certain IceCube hotspots may be unresolved blends of multiple AGN, and supports a multimessenger scenario in which high-energy neutrinos and hard X-rays originate from the same hadronic interactions, with the X-ray emission produced through cascade reprocessing.
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https://arxiv.org/abs/2512.24178
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Academic Papers
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f277165b62fd5fd0e67d1e2de4a860aa2ccaa052265f40378c70b0f8f16a5b46
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2026-01-01T00:00:00-05:00
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Tidally Trapped Two-pole Pulsations Discovered in a Close Binary with a Massive $\beta$ Cephei Star
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arXiv:2512.24185v1 Announce Type: new Abstract: Tidally tilted pulsators (TTPs), whose pulsation axis aligns with the binary's semi-major axis, represent a newly established class of oscillators in binary systems. While all previously known TTPs are either $\delta$ Scuti or subdwarf B-type stars, their existence has remained unidentified in more massive $\beta$ Cephei variables. Here, we report the discovery of tidally trapped pulsations in the massive ellipsoidal variable HD~329379, based on photometry from the Transiting Exoplanet Survey Satellite (TESS). Our analysis reveals a $\beta$ Cephei pulsator in a 2.25-day orbit whose pulsation mode amplitude is strongly modulated with the orbital frequency. Based on our analysis, we concluded that this modulation can be explained by pulsations with significantly larger amplitude near the star's two tidal poles (apsides). We interpret this as a tidally distorted quadrupole pulsation chariacteristiced by trapped two-pole pulsations, with a pulsation axis aligned with the tidal axis. This represents the first identification of such a pulsation mode in a $\beta$ Cephei star, which differs from single-sided pulsations observed in previous works, marking a rare and important discovery. Our work extends the family of TTPs beyond $\delta$ Scuti and subdwarf B-type stars to include more massive $\beta$ Cephei variables. In particular, the two-pole pulsator HD~329379 stands out as the prototype of a new class of TTPs in massive stars. These results not only provide a new insight to probe the interior structure and evolutionary state for massive stars but also offer a unique opportunity to study the interaction between pulsations and strong tidal distortions.
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https://arxiv.org/abs/2512.24185
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bf2c52a53649f367d92014895a45055460e0cee7f6c0557d275907599506a96e
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2026-01-01T00:00:00-05:00
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Connecting disc-corona physics and ionised outflows in AGN in the 2040s
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arXiv:2512.24187v1 Announce Type: new Abstract: We outline a science case for next-generation wide-field spectroscopic surveys aimed at connecting the physics of the accretion disc and X-ray corona in active galactic nuclei (AGN) with the properties of their nebular regions and circumgalactic medium (CGM). We focus on the non-linear Lx-Luv relation and on deviations from this canonical coupling encoded in $\Delta \alpha_{OX}$, the offset of the optical-to-X-ray index from the mean relation, and propose to use broad and narrow line emission and CGM nebulae as calorimeters of the ionising SED to trace different accretion "states". We propose an observational strategy based on rest-frame UV/optical spectroscopy of $\sim 10^{4}-10^{5}$ AGN, a time-domain reverberation-mapping tier for a well-defined subsample, coordinated X-ray coverage, and wide-field IFU mapping of CGM emission (including H$\alpha$ and Ly$\alpha$). From these goals we derive requirements for a future ESO facility in the 2040s: a dedicated, wide-field, high-multiplex optical-NIR spectroscopic telescope with time-domain flexibility and arcmin-scale IFU capability.
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https://arxiv.org/abs/2512.24187
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Academic Papers
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6c7d9f4a63bd5d407e46a6dea3dcd72c755b427a3e6de2468885e02e81e2c020
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2026-01-01T00:00:00-05:00
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Abundance Stratification in Type Iax SN 2020rea with TARDIS
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arXiv:2512.24203v1 Announce Type: new Abstract: Using the 1D Monte Carlo-based radiative transfer code TARDIS, we investigate the spectral evolution of the Type Iax supernova (SN) 2020rea from -7 days before to +21 days after maximum light. Our best-fit models indicate stratified, velocity-dependent abundances at early times, successfully reproducing most observed spectral features. As the SN evolves, the ejecta transition from a layered to a more homogeneous composition, posing an alternative to pure deflagration models that predict fully mixed ejecta. These results highlight the need for further investigation, as current pure deflagration models cannot fully explain the origin or spectral properties of Type Iax SNe like SN 2020rea.
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https://arxiv.org/abs/2512.24203
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Academic Papers
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3df8a56f1a17ed704f95af5887551254f28df0918e1a12fdc5adadb0e30fc284
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2026-01-01T00:00:00-05:00
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H.E.S.S. detection and multi-wavelength study of the $z \sim$ 1 blazar PKS 0346$-$27
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arXiv:2512.24228v1 Announce Type: new Abstract: PKS 0346-27 is a Low Synchrotron Peaked (LSP) blazar at redshift 0.991. The very-high-energy (VHE, E > 100 GeV) spectra of blazars are always affected by $\gamma\gamma$ absorption by the Extragalactic Background Light (EBL) and subsequently, no blazars have been detected in VHE $\gamma$-rays at redshifts exceeding 1. Extending the redshift range of VHE-detected blazars to $z \gtrsim 1$ will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S. to observe flaring high-redshift ($z \gtrsim 1$) blazars. We report on H.E.S.S. ToO and multi-wavelength observations of the blazar PKS\,0346$-$27. Along with H.E.S.S., simultaneous data from {\it Fermi}-LAT, {\it Swift} (XRT and UVOT), and ATOM have been analysed and modelled using single-zone leptonic and hadronic models. PKS~0346-27 has been detected by H.E.S.S at a significance of 6.3$\sigma$ during one night, on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux are determined. No evidence for intra-night $\gamma$-ray variability has been found. A flare in high-energy (HE, $E > 100$~MeV) $\gamma$-rays detected by {\it Fermi}-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source's Eddington limit, although alternative (e.g. multi-zone) models can not be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state SED, however, requiring implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of $\gtrsim 80$.
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https://arxiv.org/abs/2512.24228
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Academic Papers
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ab5c78590b08642364a944d3f8b5149aeb25a4b0273612e519a135c0be81d566
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2026-01-01T00:00:00-05:00
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Improved lanthanide constraints for the kilonova AT 2017gfo
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arXiv:2512.24257v1 Announce Type: new Abstract: Spectroscopic observations of the kilonova AT 2017gfo provide a unique opportunity to identify signatures from individual heavy elements freshly synthesised via the {\it r}-process, the nucleosynthetic channel responsible for producing $\sim$half of all trans-iron-group elements. Limitations in the available atomic data have historically hampered comprehensive line identification studies; however, renewed interest has led to the generation of improved (more complete and accurately calibrated) line lists for {\it r}-process species. Here we demonstrate the utility of such data, by exploiting newly generated line lists for the lanthanides to model the photospheric-phase 3.4d X-shooter spectrum of AT 2017gfo with the radiative transfer tool \textsc{tardis}. We find the data can only be reproduced by invoking a substantially diminished lanthanide mass fraction ($X_{\textsc{ln}}$) than that proposed by previous studies. Specifically, our model necessitates $X_{\textsc{ln}} \approx 2.5 \times 10^{-3}$, a value $20 \times$ lower than previously claimed. This substantial reduction in $X_{\textsc{ln}}$ is driven by our inclusion of much more complete lanthanide line information that enables better estimation of their total contribution to the observations. We encourage future modelling works to exploit all atomic data advances, and also encourage continued efforts to generate the necessary data for the remaining {\it r}-process species of interest.
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https://arxiv.org/abs/2512.24257
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Academic Papers
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fc05af9bdc56876ac09b506f44c6d221ab0c171404915bc28b63bdf213c2847c
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2026-01-01T00:00:00-05:00
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From Nbody1 to Nbody7: the Growth of Sverres Industry
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arXiv:2512.24299v1 Announce Type: new Abstract: From NBODY1 to NBODY6 : The Growth of an Industry is the title of a 1999 invited review by Sverre Aarseth, for Publications of the Astronomical Society of the Pacific (PASP). I took this as an inspiration for the title of this paper; it describes how Sverres NBODY Industry has further grown since 90s of the previous century, and how it is further flourishing and hopefully developing, in his spirit, even after the sad news of his passing away reached us. My contact and friendship with Sverre started a few decades ago being sent to Cambridge to learn NBODY5, counting input parameters, and learning about the fact that even a sophisticated code (which had already at that time quite a history) requires permanent maintenance and bug fixes. Managed by Sverre, who relentlessly ran his code and responded to the widely spread crowd of customer colleagues. There has been a phase of massive and fast development and improvements due to vectorization, parallelization, GRAPE and GPU acceleration, and Sverre has been always on top of it if not ahead, but also fully adopting ideas of collaborators, once they tested well. NBODY6++GPU and NBODY7 entered the scene, and also recent new competitors, such as PETAR or BIFROST . We all have learnt a lot from Sverre, and strive to continue in his open-minded spirit, for open source and exchange. A striking evidence for the further growth of the industry is the number of papers here (and two of them follow in this session, but also in other sessions) using and further developing the aforementioned codes, as well as the occurrence of new and competing codes, which keep the field alive.
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https://arxiv.org/abs/2512.24299
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Academic Papers
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1f9fb402e47b56b75d88f74665fb453ddb65ddeeab644144d0809ca3f0cba51a
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2026-01-01T00:00:00-05:00
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$S_8-H_0$ tension in a SI-ULDM scenario
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arXiv:2512.24309v1 Announce Type: new Abstract: We study the cosmological impact of a transient self-interaction phase in Ultra-Light Dark Matter (ULDM), focusing on its simultaneous effects on the sound horizon and the late-time growth of structure. In the presence of a quartic self-interaction, the scalar field undergoes a short-lived radiation-like phase before evolving into matter-like behaviour, inducing a localized modification of the expansion history at early times. We develop a perturbative and model-independent framework in which the self-interaction energy density is parametrized as a localized contribution to the total energy budget. Within this approach, the responses of the sound horizon and the linear growth factor can be expressed as weighted integrals over cosmic time, with distinct kernels encoding the temporal sensitivity of each observable. This structure leads to a simple analytic relation linking the corresponding early- and late-time responses, and naturally predicts correlated shifts in $H_0$ and $S_8$ whose sign and magnitude depend on the timing of the self-interaction episode. Our results show that a single transient modification of the expansion history can interpolate between early-time effects on the sound horizon and late-time suppression of structure growth within a unified physical framework, providing an analytical understanding of their joint response.
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https://arxiv.org/abs/2512.24309
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Academic Papers
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c8ad5ecd6409652ba7ebcd22d2654bc29b466b3ab9c5d403b5887aa59ca48c1d
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2026-01-01T00:00:00-05:00
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The Likelihood of Hosting Undetected Brown Dwarfs in the Solar Vicinity
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arXiv:2512.24319v1 Announce Type: new Abstract: Based on the spatial distribution of objects in the solar neighbourhood with a radius of 20 parsecs, and after correcting for the incompleteness of observational data, an expression was obtained for estimating the probability of finding an object at a given distance from the Sun. According to these estimates, with a probability of about 0.5, there exists a brown dwarf in the immediate solar vicinity (< 1.2 pc). The possible multiplicity of this hypothetical object is discussed, as well as the reasons why it has not yet been detected.
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https://arxiv.org/abs/2512.24319
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Academic Papers
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2b7fdf03bdd2bc088c35b161f760574170b9b7c4c1094e31862b66118b037654
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2026-01-01T00:00:00-05:00
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Self-Gravitating Scalar Field Configurations, Ultra Light Dark Matter and Galactic Scale Observations
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arXiv:2512.24350v1 Announce Type: new Abstract: In this thesis, we investigate the possibility that dark matter consists of ultra light spin-zero particles with mass $m \sim 10^{-22}\ \text{eV}$. We focus on the role of self-interactions, assuming all other non-gravitational couplings to Standard Model particles are negligible. Such ultra light dark matter (ULDM) is expected to form stable self-gravitating scalar field configurations (solitons), whose properties depend on the particle mass and self-coupling $\lambda$. Using solutions of the Gross-Pitaevskii-Poisson equations, we explore how galactic-scale observations can constrain $m$ and $\lambda$. We show that observational upper limits on the mass enclosed in central galactic regions can probe both attractive and repulsive self-interactions with strengths $\lambda \sim \pm 10^{-96} - 10^{-95}$. We further demonstrate that self-interactions can allow ULDM to describe observed rotation curves as well as satisfy an empirical soliton-halo mass relation in low surface brightness galaxies for $m \sim 10^{-22}\ \text{eV}$ and $\lambda \gtrsim 10^{-90}$. We also study tidal effects in satellite dwarf galaxies and find that attractive self-interactions can extend their lifetimes over cosmological timescales, allowing ULDM to evade recent constraints derived for the non-interacting case. Finally, we explore machine learning based inference of dark matter and baryonic parameters from galaxy rotation curves, showing that neural networks can recover parameters consistent with observations.
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https://arxiv.org/abs/2512.24350
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Academic Papers
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dec79eb9a10fb466026cf9425a835614f5915379293353e7578e51c685badfa2
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2026-01-01T00:00:00-05:00
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Integrated Sachs-Wolfe maps from the Gower Street $w$CDM simulations
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arXiv:2512.24369v1 Announce Type: new Abstract: The late-time linear Integrated Sachs-Wolfe (ISW) effect directly probes the dynamics of cosmic acceleration and the nature of dark energy. Detecting these weak, secondary temperature anisotropy signals of the CMB requires accurate theoretical predictions of their amplitude across cosmological models. By extending the pyGenISW package, previously limited to $\Lambda$CDM, we aim to generate full-sky ISW maps for a suite of 791 $w$CDM cosmologies using the Gower Street N-body simulations, thereby enabling ISW analyses across a broader dark-energy parameter space. We make our code and ISW data publicly available. We compute the ISW signals by tracing the time evolution of the gravitational potential across large-volume simulations that span dark energy equation of state parameters from phantom to quintessence, $-1.79 \lesssim w \lesssim -0.34$. These data are projected onto the sphere using HEALPix to obtain full-sky temperature maps. We validate our pipeline by comparing the measured ISW angular power spectra and ISW-density cross-correlations against linear theory expectations ($2 \leq \ell \leq 200$) computed with benchmarks from the pyCCL library. The agreement is excellent across the multipole range where the ISW contribution is expected to dominate, confirming the reliability of our modelling of gravitational-potential evolution. With additional tests of the ISW signal's strength in density extrema, as well as comparing all models to a reference $\Lambda$CDM cosmology, we found that quintessence-like models ($w > -1$) show higher ISW amplitudes than phantom models ($w < -1$), consistent with enhanced late-time decay of gravitational potentials. The consistency of our $w$CDM ISW maps and their agreement with theory predictions confirm the robustness of our methodology, establishing it as a reliable tool for theoretical and observational ISW-LSS analyses.
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https://arxiv.org/abs/2512.24369
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f7565b4cbb8f46e742bbf28542f21577cf49c95e9aa2aecd704db59251869368
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2026-01-01T00:00:00-05:00
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A millimeter methanol maser ring tracing the deceleration of the heat wave powered by the massive protostellar accretion outburst in G358.93-0.03 MM1
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arXiv:2512.24380v1 Announce Type: new Abstract: We present multi-epoch, multi-band ALMA imaging of the new Class II millimeter methanol masers excited during the accretion outburst of the massive protostar G358.93-0.03 MM1. The highest angular resolution image (24 mas $\approx$ 160 au) reveals a nearly complete, circular ring of strong maser spots in the 217.2992 GHz ($v_t$=1) maser line that closely circumscribes the dust continuum emission from MM1. Weaker maser emission lies inside the eastern and southern halves of the maser ring, generally coincident with the centimeter masers excited during the outburst, but avoiding the densest parts of the hot core gas traced by high excitation lines of CH$_3$CN. Using a variety of fitting techniques on the image cubes of the two strongest maser lines, each observed over 3-4 epochs, we find the diameter of the ring increased by $\gtrsim$60% (from $\approx$1100 to $\approx$1800 au in the 217 GHz line) over 200 days, consistent with an average radial propagation rate of $\approx$0.01c, while the maser intensity declined exponentially. Fitting the angular extent of the millimeter masers versus time yields a power law of index 0.39$\pm$0.06, which also reproduces the observed extent of the 6.7 GHz masers in the first VLBI epoch of R. A. Burns et al. (2020). This exponent is consistent with the prediction of radius vs. time in the Taylor-von Neumann-Sedov self-similar solution for an intense spherical explosion from a point source ($R \propto t^{2/5}$). These results demonstrate the explosive nature of accretion outbursts in massive protostars and their ability to generate subluminal heat waves traceable by centimeter and millimeter masers for several months as the energy traverses the surrounding molecular material.
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https://arxiv.org/abs/2512.24380
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2002f65e13d07595f1f1e24198f33be6264305fa227813c46b4ce9834f84d20f
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2026-01-01T00:00:00-05:00
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A closer look at the young stellar group around Sh 2-295
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arXiv:2512.24388v1 Announce Type: new Abstract: Star formation is governed by multiple physical processes, making it inherently complicated. One excellent example is the Canis Major OB1/R1 Association, whose complex history of star formation is related to different episodes. Three supernova (SN) events potentially altered the environment and impacted star formation and stellar evolution. Prior investigations revealed two stellar groups of different ages associated with GU CMa and Z CMa. This work focusses on identifying the low-mass young stellar population near FZ CMa, located between these two groups and spatially related to the H II region Sh 2-295. Our main goal is to verify whether this group is age-mixed and characterise its physical properties. We analysed multi-object spectroscopic data acquired with Gemini/GMOS to search for typical features of T Tauri stars (TTs) and to determine their spectral types. Lithium absorption line ($\lambda$ 6708 $\mathring{A}$) was used as a youth indicator, while H$\alpha$ emission was investigated to probe accretion activity. We also derived ages based on optical photometry from Gaia DR3 and compared the projected spatial distribution to diffuse infrared (IR) emission. We identified 29 TTs, including six new members of the association and three Classical TTs (CTTs). The equivalent width of the Li I absorption line suggests an age of $8.1^{+2.1}_{-3.8}$ Myr, while optical photometric data indicate stellar ages ranging from $\sim$1 to 14 Myr. Younger stars are concentrated around Sh 2-295, whereas the older ones are more widely dispersed. We increased the number of known TTs related to the CMa association. Our results support a scenario of multiple star-formation episodes, including a younger group that may have been triggered by the expansion of Sh 2-295. The influence of SN events appears limited in this context.
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https://arxiv.org/abs/2512.24388
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dd274e5c782b739ee35a9b95cae415d7d903afc7397ba8937fe7902511dbb484
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2026-01-01T00:00:00-05:00
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OmniCosmos: Transferring Particle Physics Knowledge Across the Cosmos
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arXiv:2512.24422v1 Announce Type: new Abstract: Foundation models build an effective representations of data that can be deployed on diverse downstream tasks. Previous research developed the OmniLearned foundation model for collider physics and showed that it could significantly advance discovery potential across collider experiments. In this paper we go beyond collider physics and show that Foundation Models trained on collider data can help improve the prediction of cosmological parameters and to predict halo and galaxy velocities in different datasets from CosmoBench. This is the first time a collider physics model is shown to generalize across scientific fields.
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https://arxiv.org/abs/2512.24422
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Academic Papers
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f7d87af3c19331bc84b58ad34d9e69eb19e1985208874879b7a0587480613837
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2026-01-01T00:00:00-05:00
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A Convolutional Neural Network for the Recovery of Transfer Functions From Velocity-Resolved Reverberation Mapping Data
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arXiv:2512.24433v1 Announce Type: new Abstract: One of the hallmarks of active galactic nuclei are that they are highly variable with time. In watching the spectra vary it has been observed that the emission-lines often appear to "reverberate" -- that is they vary in response to continuum variations assumed to originate close to the black hole. This critical observation underlies the reverberation mapping technique, an elegant physics experiment that has allowed us to characterize the environment around many supermassive black holes in nearby active galactic nuclei. Recent observations are of such quality that the response can be measured as a function of velocity across the emission-line, and in doing so we can construct velocity-delay maps that show the structure and physics of the gas in the broad-line region better than any other measurement to date. Unfortunately constructing such maps requires a deconvolution, and given that the data are often noisy and with gaps such deconvolutions are non-trivial. Here we present a novel deconvolution method for the recovery of velocity-delay maps using a custom convolutional neural network architecture, showcasing that such methods have great promise for the deconvolution of reverberation mapping data products. While we have designed this new method with the BLR in mind, in principle this technique could be applied to any reverberation deconvolution problem, including in the accretion disk and torus.
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https://arxiv.org/abs/2512.24433
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0fbe139c61f1198a16ec0df535d89531db2fd52a86d529c823e8d42268fb753c
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2026-01-01T00:00:00-05:00
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Nine years of UVIT: assessing sensitivity variation
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arXiv:2512.24475v1 Announce Type: new Abstract: The Ultra-Violet Imaging Telescope (UVIT) is one of the five payloads onboard the first Indian multiwavelength astronomical observatory, AstroSat, launched by the Indian Space Research Organisation on 28 September 2015. UVIT, designed for simultaneous imaging in the far-ultraviolet (FUV; 1300-1800 {\AA}) and near-ultraviolet (NUV; 2000-3000 {\AA}) channels, has completed nine years in orbit in 2024 despite the failure of the NUV channel in 2018. As the FUV optics is subject to possible reduction in sensitivity due to microscopic amounts of contaminants, we used the FUV data acquired by UVIT over the past nine years on the open cluster NGC 188 and the white dwarf HZ 4 to study sensitivity variations in the UVIT FUV channel. Our findings indicate no significant reduction in the sensitivity of the FUV channel over the last nine years, with no significant episodic variations due to unknown causes.
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https://arxiv.org/abs/2512.24475
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bef480ad079baca27043b1ee3f609353754fabf82758660f9b06f055b8b7a023
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2026-01-01T00:00:00-05:00
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Understanding Solar Flares and Energetic Events: Open questions, observational requirements, and instrumental needs over the coming decade
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arXiv:2512.24479v1 Announce Type: new Abstract: Solar flares are the largest energy-release events in the Solar System, allowing us to study fundamental physical phenomena under extreme conditions. Those include magnetic reconnection, particle acceleration, radiation transport, and various plasma physics processes, all of which occur throughout the heliosphere and rest of the Universe. Flares and eruptive events are also components of geo-effective space weather. Their impacts from a space weather perspective are numerous, such as harm to satellites, disruption to GPS, communications and power systems, and impacts on passenger air travel. A comprehensive understanding of solar flares is therefore not just a compelling science problem, but also important for national security and infrastructure. This white paper (WP) addresses critical open science questions related to solar flares. Key observations and capabilities required to make significant advancements over the coming decade are identified. The UK has a robust and vibrant solar flare community. We are key partners in international collaborations, and also provide instrumentation for existing and upcoming ESA/NASA/JAXA space missions. Continuing this effort over the coming decade is vital to maintain UK leadership in this field, achieve Solar System Advisory Panel roadmap goals, and to work under the UK Space Agency's National Space Strategy Pillars. Several complementary WPs have been submitted that discuss instruments or concepts that would directly address the observational requirements we describe (including: SPARK, solar optimised IFUs, Solar-C/EUVST, and OSIRIS), as well as required numerical modelling efforts and infrastructure.
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https://arxiv.org/abs/2512.24479
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c327784dd1c65cf1a06670b9ea957dfac522c7f41b5ebaba9deef00b0bb6b002
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2026-01-01T00:00:00-05:00
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3D Radiative MHD Modeling of Particle Beam Heating of the Solar Atmosphere
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arXiv:2512.24507v1 Announce Type: new Abstract: While solar flares are primarily associated with enhanced ultraviolet and X-ray emission, a subset of flares exhibit significant continuum brightening in visible light and are classified as white-light flares (WLFs). Despite extensive observational and modeling efforts, the physical mechanisms responsible for the compact, short-lived photospheric brightenings in WLF kernels observed during the impulsive phase of solar flares remain uncertain. Thick-target electron-beam models typically deposit energy in the upper chromosphere, and their ability to reproduce the magnitude and spatial localization of photospheric continuum enhancements observed in white-light flare kernels remains an open question. To investigate the role of realistic atmospheric structuring and multidimensional transport in flare energy deposition, we perform three-dimensional radiative MHD simulations of electron-beam heating using the StellarBox code for beam fluxes of $10^{12}$ erg\,s$^{-1}$\,cm$^{-2}$ and low-energy cutoffs of 10--25\,keV. We then compute Fe\,I 6173\,\AA~Stokes profiles using the RH 1.5D radiative transfer code for direct comparison with Helioseismic and Magnetic Imager (HMI) observations. The simulations produce strong upper-chromospheric heating, multiple shock fronts, and continuum enhancements up to a factor of 2.5 relative to pre-flare levels, comparable to continuum enhancements observed during strong X-class white-light flares. Comparison with one-dimensional RADYN simulations highlights the influence of fine-scale structuring on flare dynamics and continuum emission that arises in three-dimensional geometry.
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https://arxiv.org/abs/2512.24507
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818a80df670b2aaafe43b4604a0eab2811feb487750cb1180640daa26d817d10
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2026-01-01T00:00:00-05:00
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The Redshifts from 122 Bands: Comparative Redshift Forecast for Low-Resolution Spectra from SPHEREx and 7-Dimensional Sky Survey (7DS)
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arXiv:2512.24537v1 Announce Type: new Abstract: The recently initiated SPHEREx and 7DS surveys will deliver low-resolution spectra ($R\approx 30-130$) for hundreds of millions of galaxies over the optical to near-infrared range ($0.4-5.0\mu m$), covering a wide sky area without sample selection. These unique datasets will improve redshift estimation and provide a rich redshift catalog for the community. In this study, we forecast the performance of widely-used photometric redshift estimation methods using simulated SPHEREx and 7DS data. Four template-fitting approaches and two machine-learning (ML) methods are used to derive photometric redshifts from low-resolution spectrophotometric data. We measure redshifts using mock catalogs based on the GAMA and COSMOS galaxy samples and achieve high precision for bright (13 < i < 18) galaxies, with $\sigma_{NMAD}\lesssim 0.005$, bias $\lesssim 0.005$, and a catastrophic failure rate $\lesssim 0.005$ for all methods employed. We find that the combined SPHEREx + 7DS dataset significantly improves redshift estimation compared to using either the SPHEREx or 7DS datasets alone, highlighting the synergy between the two surveys. Moreover, we compare the redshift estimation performance across magnitude ranges for the different methods and examine the probability distribution functions (PDFs) produced by the template-fitting approaches. As a result, we identify some factors that can affect the redshift measurements, like treatments on dust extinction or inclusion of flux uncertainty in the ML model. We also show that the PDFs are relatively well calibrated, although the confidence intervals are generally underestimated, particularly for bright galaxies in the template-fitting methods. This study demonstrates the strong potential of SPHEREx and 7DS to deliver improved redshift measurements from low-resolution spectrophotometric data, underscoring the scientific value of jointly utilizing both datasets.
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https://arxiv.org/abs/2512.24537
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c68c6ac2ce45af6827020bd076f35f66893985b4561dfbdc58f142e71d670091
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2026-01-01T00:00:00-05:00
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Seafloor Weathering and Stochastic Outgassing Unlikely to Significantly Shorten the Future Lifespan of Earth's Terrestrial Biosphere
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arXiv:2512.24538v1 Announce Type: new Abstract: Current understanding suggests that as the Sun brightens in the far future, Earth's carbonate-silicate cycle will offset increasing temperatures by drawing CO$_2$ out of the atmosphere, ultimately leading to the extinction of all terrestrial plant life via either overheating or CO$_2$ starvation. Most previous estimates put the future lifespan of Earth's terrestrial biosphere at $\sim$1 billion yr, but recent work used a new coupled climate-continental weathering model with up-to-date parameter constraints to revise this estimate upward to 1.6-1.86 billion yr. In this study, we extend the model to examine the impacts of seafloor weathering and stochastic variations in CO$_2$ outgassing rates on the remaining lifespan of Earth's terrestrial biosphere. We find that if seafloor weathering has a stronger feedback than continental weathering and accounts for a large portion of global silicate weathering, then the remaining lifespan of the terrestrial biosphere can be shortened, but a lifespan of more than 1 billion yr (Gyr) remains likely. Similarly, stochastic fluctuations in outgassing rates can have a significant impact if the size of the fluctuations exceed those observed over the last 1 billion yr. The impact of weak seafloor weathering and lower variability stochasticity are minor. Our work provisionally supports a lengthened lifespan of Earth's terrestrial biosphere, suggests robustness of this lengthened lifespan to planetary parameters that may vary among exoplanets, and identifies seafloor weathering as a key process that requires further study and constraint.
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https://arxiv.org/abs/2512.24538
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d14a0dce0358bbda361f3ff6b06b0008a2412cfcb89c91518c2d576b08cf046a
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2026-01-01T00:00:00-05:00
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Evidence for the transition from thermal to non-thermal emission in the prompt emission of GRB 161117A
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arXiv:2512.24563v1 Announce Type: new Abstract: GRB 161117A is a long-duration GRB with three main overlapping peaks. By analyzing the time-resolved spectra of its data observed with the Gamma-Ray Burst Monitor (GBM) on board the Fermi mission, we find that the spectral evolution shows a transition from thermal (single BB) to hybrid (PL$+$BB), and finally to non-thermal (Band and CPL) emissions. Such a transition suggests that the jet composition of GRB 161117A should be changed from a fireball to a Poynting-flux-dominated jet. The bulk Lorentz factor ($\Gamma_{\rm ph}$), radii ($R_{\rm ph}$ and $R_{0}$), magnetization factor at the central engine ($\sigma_0$), and dimensionless entropy ($\eta$) of the outflow can be inferred by invoking the observed quasi-thermal component within two models (e.g., pure fireball and hybrid). It is found that $\Gamma_{\rm ph}$ seems to be tracking with the light curve, and $R_{0}$ remains a constant at $\sim$ $10^{8}$ cm. The low magnetization ($1+\sigma_0 \sim$ 1) and high dimensionless entropy ($\eta \gg$ 1) during the first seven time-intervals suggest to be a pure fireball outflow. Moreover, we also estimate the lower limit of magnetization parameter at the photosphere radius ($\sigma_{\rm ph}\sim 1.4$ and 0.75) for late phase via the non-thermal spectra, and it indicates that the particle acceleration mechanism is dominated by internal shocks rather than magnetic dissipation processes. Finally, the $\nu \bar{\nu}$ annihilation mechanism of NDAF model to explain the thermal emission of GRB 161117A is also discussed.
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https://arxiv.org/abs/2512.24563
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0263e9fb26328cecd7b6dbd6fc1073a7d28596bcaa670a7ab6e8d3442bc7d73c
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2026-01-01T00:00:00-05:00
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Inferring Solar Magnetic fields From the Polarization of the Mg II h and k Lines
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arXiv:2512.24578v1 Announce Type: new Abstract: The polarization of the Mg II h and k lines holds significant diagnostic potential for measuring chromospheric magnetic fields, which are crucial for understanding the physical processes governing the energy transport and dissipation in the solar upper atmosphere, as well as the subsequent heating of the chromosphere and corona. The Chromospheric Layer Spectropolarimeter was launched twice in 2019 and 2021, successfully acquiring spectropolarimetric observations across the Mg II h and k lines. The analysis of these observations confirms the capability of these lines for inferring magnetic fields in the upper chromosphere. In this review, we briefly introduce the physical mechanisms behind the polarization of the Mg II h and k lines, including the joint action of the Zeeman and Hanle effects, the magneto-optical effect, partial frequency redistribution, and atomic level polarization. We also provide an overview of recent progress in the interpretation of the Stokes profiles of the Mg II h and k lines.
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https://arxiv.org/abs/2512.24578
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72b80ae07885a7ef4ac4bfb02c67c56144b8d4e5d805c888a417ba5104f2e2ce
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2026-01-01T00:00:00-05:00
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Dust destruction in bubbles driven by multiple supernovae explosions
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arXiv:2512.24670v1 Announce Type: new Abstract: Dust lifetime derived from an isolated supernova (SN) evolution in the interstellar medium is known to be an order of magnitude shorter than the time needed to replenish dust mass by its production in various Galactic sources. We show, using 3-D numerical hydrodynamical simulations, that destruction of dust in the case of multiple SNe in a star cluster is markedly different from that in an isolated SN. We find that the mass of dust destroyed in the bubble does not grow for a considerable time, while SNe continue to explode. This regime is attained at saturation timescale, which is proportional to SNe rate in cluster. We show that the mass of dust destroyed in bubble per SN decreases for higher SN rate. Thus, the destruction efficiency -- defined as the ratio of the the total mass of dust destroyed by clustered SNe to that destroyed by the same number of isolated SNe -- in bubbles evolved in a homogeneous medium drops for massive clusters, e.g. around clusters with $M_\ast > 4\times 10^4 M_\odot$ it is less $0.4$\%. For lower mass clusters, the efficiency is proportional to the average time delay between SNe. We found that each cluster with $M_\ast < 4\times 10^4 M_\odot$ destroys the same mass of dust as a single isolated SN. In a clumpy medium in bubbles formed around clusters with $M_\ast \sim 4\times 10^4 M_\odot$ and up to 4 times around $M_\ast \sim 8\times 10^5 M_\odot$. We argue that the interstellar dust swept up by multiple SNe almost completely survives in the shells of bubbles around such massive clusters. Therefore, the destruction of the interstellar dust is controlled by SNe in low-mass clusters. We point out that the interstellar dust lifetime for a given SN rate is at least a factor $\sim 10$ longer as compared to the estimates derived from an isolated SN. (abridged)
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https://arxiv.org/abs/2512.24670
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86897caa2bf7fcae34baeba66d687390991043e856385d20607bd036abebaa49
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2026-01-01T00:00:00-05:00
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An Effective Theory for Biased Tracers via the Boltzmann-Equation Approach
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arXiv:2512.24672v1 Announce Type: new Abstract: We develop an effective theory for biased tracers formulated at the level of the Boltzmann equation, providing a unified description of density and velocity bias. We introduce a general effective collision term in the tracer Boltzmann equation to encode tracer dynamics that are intrinsically different from those of dark matter. This collision operator leads to modified continuity and Euler equations, with source terms reflecting the collision-term physics. At linear order, this framework predicts time- and scale-dependent bias parameters in a self-consistent manner, encompassing peak bias as a special case while clarifying how velocity bias and higher-derivative effects arise. Applying the resulting bias model to redshift-space distortions, we show that the Boltzmann-equation approach reproduces the power spectrum of biased tracers obtained in the Effective Field Theory of Large-Scale Structure up to $k^4$ terms with fewer independent parameters.
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https://arxiv.org/abs/2512.24672
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25d4d17092e452e9827d86d3b766d15e0cf1677dc41a596921d899824440f6f1
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2026-01-01T00:00:00-05:00
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Destruction of the interstellar dust by a supernova
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arXiv:2512.24677v1 Announce Type: new Abstract: Destruction of the interstellar dust proceeds primary behind supernova shocks. The previous estimates of the mass of the interstellar dust destroyed in the SN remnant do not take into account the physical properties of the ambient medium. Here we consider how some parameters, i.e. gas density and metallicity, can influence the destruction of the interstellar dust. We show that there are two regimes of the interstellar dust grains destruction in SN remnants: rapid and almost complete in compact low-mass SN remnants expanding in dense medium, and gradual and weak destruction in massive remnants evolving in the low-dense environment. When time for thermal sputtering is close to the dynamical one, i.e. to the SN remnant age, the mass of the interstellar dust destroyed in the SN remnant reaches its maximum value. We find that change of the ambient gas density results in the reduction of the dust mass logarithmically. We argue that dust cooling suppresses the interstellar dust destruction up to a factor of 1.6 by mass. This factor decreases for higher density of the ambient medium. We found that the dust mass depends linearly on gas metallicity as ${\rm log}~M_d \sim {\rm [Z/H]}$ or, in other words, on the dust-to-gas ratio as $M_d \sim \zeta_d$. In turn, the destruction efficiency is higher in low-metallicity environments due to relatively longer adiabatic phase. We point out that the mass of the interstellar dust destroyed per one SN in a high density environment of the high star formation regions like in local ultraluminous infrared and high-redshift massive galaxies is about several times smaller than that in the Milky Way diffuse medium.
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https://arxiv.org/abs/2512.24677
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ff0aee8d5cf40f433e2a7863e42bada9be83148478b723f9033ccc964e167259
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2026-01-01T00:00:00-05:00
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The role of PSR J0614-3329 in defining the high-density matter at Neutron star cores
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arXiv:2512.24729v1 Announce Type: new Abstract: In this work, we investigate how astrophysical observations from NICER and GW data constrain the matter properties at high densities, with a primary focus on the recent PSR J0614-3329 data. We have constructed three distinct classes of an ensemble of agnostic equation of state by speed of sound parametrisation. Bayesian inference is then employed to constrain the EoS construction parameters-namely, the squared speed of sound and chemical potential at each interpolation segment-using the observational data. Both the NICER and GW constraints hint towards a smoother EoS where PT occurs late, significantly reducing the maximum mass of NS. Also, the maximum-mass and maximum-compact sequences are distinctly different, as the former allows for the maximally stiff EoS to maximise the star mass. In contrast, the latter prefers a softer low-density and stiffer high-density EoS to maximise the compactness. The Bayesian analysis demonstrates that the observational bounds are effective in significantly constraining the low-density region of the equation of state. It is also seen that the astrophysical bound prefers the phase transition in the intermediate-density range and also prefers a small density jump for a discontinuous equation of state.
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https://arxiv.org/abs/2512.24729
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f73e52e819ea1b6bb4a50fefca00d83fcc5d90920a37f38d85966d46fb1a2905
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2026-01-01T00:00:00-05:00
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Coronal flux tube illuminated by strong shock spot: New Year's Eve solar eruption of 2023-Dec-31
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arXiv:2512.24749v1 Announce Type: new Abstract: Powerful solar eruptions are known to produce fast and wide shock waves in the solar corona and inner heliosphere. The relationship between the coronal shock waves, solar energetic particles and different types of radio emission is a subject of long-lasting research activity. In this work, we perform a case study of 31 December 2023 eruption that occurred near eastern limb of the Sun. It produced a X5.0 class X-ray flare, a global EUV wave, a fast $\sim3000$ km/s Coronal Mass Ejection, strong radio emissions (including several type III and type II bursts), solar energetic particles in-situ, and long duration high-energy gamma-ray emission. We employ a technique that combines the reconstructed coronal shock from observations with background coronal MHD simulations to produce shock-mediated synthetic radio spectrum, assuming local emission at plasma frequency. We show that transient high Mach number and quasi-perpendicular coronal shock region explains both a ``hot flux tube'' precursor seen in EUV observations and reverse drifting radio spectral features observed by ground-based facilities. The occurrence of this evanescent strong shock patch was observed when it propagated across pseudo-streamer's cusp where the magnetic field was particularly low. We also find evidence that, at higher coronal altitudes, the low-frequency type II radio burst detected by several spacecraft, is triggered by the interaction of the shock with the heliospheric current sheet. This study provides additional evidence that high-$M_A$ regions of coronal shock surface are instrumental in energetic particle phenomenology.
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https://arxiv.org/abs/2512.24749
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8345bf0adfde6e7ac7cc7a93adeb361f2aa23529d5213d405c52ff98341e8148
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2026-01-01T00:00:00-05:00
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LUNCH: A Lightweight Unified Deep-Learning Framework for General Transients Classification in High-Energy Time-Domain Astronomy
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arXiv:2512.24764v1 Announce Type: new Abstract: The increasing data volume of high-energy space monitors necessitates real-time, automated transient classification for multi-messenger follow-up. Conventional methods rely on empirical features like hardness ratios and reliable localization, which are not always precisely available during early detection. We developed the Lightweight Unified Neural Classifier for High-energy Transients (LUNCH) - an end-to-end deep-learning framework that performs general transient classification directly from raw multi-band light curves, eliminating the need for background subtraction or source localization. Its dual-scale architecture fuses long- and short-scale temporal evolution adaptively. Evaluated on 15 years of Fermi/GBM triggers, the optimal model achieves 97.23% accuracy when trained on complete energy spectra. A lightweight version using only three broad energy bands retains 95.07% accuracy, demonstrating that coarse spectral information fused with temporal context enables robust discrimination. The system significantly outperforms the GBM in-flight classifier on three months of independent test data. Feature visualization reveals well-separated class clusters, confirming physical interpretability. LUNCH combines high accuracy, low computational cost, and instrument-agnostic inputs, offering a practical solution for real-time in-flight processing that enables timely triggers for immediate multi-wavelength and multi-messenger follow-up observations in future time-domain missions.
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https://arxiv.org/abs/2512.24764
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c5f3206a44330efab7b00d89cebd3a4049c8799e3278068a1287c0a3db262c91
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2026-01-01T00:00:00-05:00
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TTC: Transformer-based TDE Classifier for the Wide Field Survey Telescope (WFST)
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arXiv:2512.24782v1 Announce Type: new Abstract: We propose the Transformer-based Tidal disruption events (TDE) Classifier (\texttt{TTC}), specifically designed to operate effectively with both real-time alert streams and archival data of the Wide Field Survey Telescope (WFST). It aims to minimize the reliance on external catalogs and find TDE candidates from pure light curves, which is more suitable for finding TDEs in faint and distant galaxies. \texttt{TTC} consists of two key modules that can work independently: (1) A light curve parametric fitting module and (2) a Transformer (\texttt{Mgformer})-based classification network. The training of the latter module and evaluation for each module utilize a light curve dataset of 7413 spectroscopically classified transients from the Zwicky Transient Facility (ZTF). The \texttt{Mgformer}-based module is superior in performance and flexibility. Its representative recall and precision values are 0.79 and 0.76, respectively, and can be modified by adjusting the threshold. It can also efficiently find TDE candidates within 30 days from the first detection. For comparison, the parametric fitting module yields values of 0.72 and 0.40, respectively, while it is $>$10 times faster in average speed. Hence, the setup of modules allows a trade-off between performance and time, as well as precision and recall. \texttt{TTC} has successfully picked out all spectroscopically identified TDEs among ZTF transients in a real-time classification test, and selected $\sim$20 TDE candidates in the deep field survey data of WFST. The discovery rate will greatly increase once the differential database for the wide field survey is ready.
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https://arxiv.org/abs/2512.24782
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901658dc81eb4127de9bd3c63941a54cf85767452199e4ce0b23461cfb79e879
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2026-01-01T00:00:00-05:00
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Scalable Stellar Parameter Inference Using Python-based LASP: From CPU Optimization to GPU Acceleration
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arXiv:2512.24840v1 Announce Type: new Abstract: To enhance the efficiency, scalability, and cross-survey applicability of stellar parameter inference in large spectroscopic datasets, we present a modular, parallelized Python framework with automated error estimation, built on the LAMOST Atmospheric Parameter Pipeline (LASP) originally implemented in IDL. Rather than a direct code translation, this framework refactors LASP with two complementary modules: LASP-CurveFit, a new implementation of the LASP fitting procedure that runs on a CPU, preserving legacy logic while improving data I/O and multithreaded execution efficiency; and LASP-Adam-GPU, a GPU-accelerated method that introduces grouped optimization by constructing a joint residual function over multiple observed and model spectra, enabling high-throughput parameter inference across tens of millions of spectra. Applied to 10 million LAMOST spectra, the framework reduces runtime from 84 to 48 hr on the same CPU platform and to 7 hr on an NVIDIA A100 GPU, while producing results consistent with those from the original pipeline. The inferred errors agree well with the parameter variations from repeat observations of the same target (excluding radial velocities), while the official empirical errors used in LASP are more conservative. When applied to DESI DR1, our effective temperatures and surface gravities agree better with APOGEE than those from the DESI pipeline, particularly for cool giants, while the latter performs slightly better in radial velocity and metallicity. These results suggest that the framework delivers reliable accuracy, efficiency, and transferability, offering a practical approach to parameter inference in large spectroscopic surveys. The code and DESI-based catalog are available via \dataset[DOI: 10.12149/101679]{https://doi.org/10.12149/101679} and \dataset[DOI: 10.12149/101675]{https://doi.org/10.12149/101675}, respectively.
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https://arxiv.org/abs/2512.24840
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439c6b9e768c24a5e5e62f69efc32150c0f55293d7b061c6c85e7fc6149fce27
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2026-01-01T00:00:00-05:00
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Resolving the Origins and Pathways of Ionizing Radiation Escape with UV Integral Field Spectroscopy
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arXiv:2512.24895v1 Announce Type: new Abstract: The Epoch of Reionization marks the last major phase transition in the early Universe, during which the majority of neutral hydrogen once filling the intergalactic medium was ionized by the first galaxies. The James Webb Space Telescope (JWST) is now identifying promising galaxy candidates capable of producing sufficient ionizing photons to drive this transformation. However, the fraction of these photons that escape into intergalactic space--the escape fraction--remains highly uncertain. Stellar feedback is thought to play a critical role in carving low-density channels that allow ionizing radiation to escape, but the dominant mechanisms, their operation, and their connection to observable signatures are not well understood. Local analogs of high-redshift galaxies offer a powerful alternative for studying these processes, since ionizing radiation is unobservable at high redshift due to intergalactic absorption. However, current UV space-based instrumentation lacks the spatial resolution and sensitivity required to fully address this problem. The core challenge lies in the multiscale nature of LyC escape: ionizing photons are generated on scales of 1--100 pc in super star clusters but must traverse the circumgalactic medium which can extend beyond 100 kpc. The proposed Habitable Worlds Observatory (HWO) will provide a platform for future UV instruments capable of resolving these scales. In this article, we present a science case for understanding how LyC photons escape from star-forming galaxies and define the observational requirements for future instruments aboard HWO, including a UV integral field spectrograph (IFS).
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https://arxiv.org/abs/2512.24895
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d75b65497c7e82fbda9799dd0e1b6518e02e43bf19593b9e1d568afa92de4530
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2026-01-01T00:00:00-05:00
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Cosmological dynamics and observational constraints of an interacting early scalar field coupled to radiation
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arXiv:2512.24918v1 Announce Type: new Abstract: We study the cosmic evolution of an interacting scalar field radiation model, in which a minimally coupled scalar field exchanges energy with the radiation sector through an exponential coupling. Extending previous formulations, a non-relativistic matter component is included explicitly, which allows a self consistent description of cosmological dynamics from the radiation-dominated era to late-time acceleration. Analytical expressions for the background expansion are derived and characterized using kinematic diagnostics. We constrain the model using observational Hubble data, Type Ia Supernovae, baryon acoustic oscillations (including DESI DR2), and compressed cosmic microwave background distance information, performing a Bayesian MCMC analysis. The interaction parameter is found to be consistent with zero, though small deviations from standard radiation scaling are allowed. These deviations can partially alleviate the Hubble tension by modifying the sound horizon, but this is accompanied by correlated shifts in the matter density. The reconstructed expansion history remains close to LCDM at late times. Model comparison suggest that the interacting scenario is statistically competitive but not decisively preferred by current background data.
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https://arxiv.org/abs/2512.24918
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e5fc47e59e717d8ea1719dafece056ef7a7bf4c147ba4a1b1e9062d272e6e7ff
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2026-01-01T00:00:00-05:00
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Discovery of a galaxy associated with the HI cloud FAST J0139+4328
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arXiv:2512.24924v1 Announce Type: new Abstract: The search for ``dark galaxies,'' a key prediction of the lambda cold dark matter, has yielded few viable candidates. Recently, FAST J0139+4328 was reported as the first isolated dark galaxy in the nearby universe, based on a neutral hydrogen (HI) detection and a non-detection in the Pan-STARRS1 survey. To verify the nature of this candidate, we obtained deep optical imaging, using the $1.4\,\mathrm{m}$ \textit{Milankovi\'c} and $0.6\,\mathrm{m}$ \textit{Nedeljkovi\'c} telescopes, and spectroscopic follow-up of the field. We report the unambiguous discovery of a low-surface-brightness (LSB) optical counterpart at the location of the HI cloud. Furthermore, the detection of H$\alpha$ emission via the $6\,\mathrm{m}$ Big Telescope Alt-Azimuthal (BTA) confirms that the stellar system lies at a redshift consistent with the HI source, establishing their physical association. Through detailed photometry and employing color-dependent mass-to-light scaling relations, we derive a total stellar mass of $M_\star = (7.2 \pm 3.7) \times 10^6\, M_{\odot}$, about an order of magnitude higher than the previously estimated upper limit. Using the literature HI mass, this implies a gas-to-stellar mass ratio of $M_{\mathrm{HI}} / M_{\star} = 11.5 \pm 6.4$. Our findings demonstrate that FAST J0139+4328 is not a dark galaxy but an extremely gas-rich LSB dwarf galaxy, whose stellar component was simply below the detection limit of the Pan-STARRS1 survey. This reclassification resolves the status of this prominent dark galaxy candidate and underscores the necessity of deep optical follow-up to classify faint HI-selected systems.
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https://arxiv.org/abs/2512.24924
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fd01489ef156ff3b716ad3ac60253f77edc9aa0852f454c026e0f2a4aaee053c
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2026-01-01T00:00:00-05:00
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Searching for Periodicity in FRB 20240114A
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arXiv:2512.24936v1 Announce Type: new Abstract: FRB 20240114A is extraordinarily active, and therefore presents an opportunity to search for the periodicity predicted by magnetar models of Fast Radio Bursts (FRB). Zhang, et al. (2025) observed 11,553 bursts, including 3196 on MJD 60381 (March 12, 2024). We find no significant peak in the periodogram of those bursts, which occur within 15628 s, short enough that even with a characteristic slowing age of 1 year a signal with period $\ge 0.1\,$s it would not significantly dephase within the observation. Introducing modulation artificially shows that an amplitude of 0.15 would have been detected robustly. Implications for magnetar models of FRB are briefly considered.
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https://arxiv.org/abs/2512.24936
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27419794622b28063a86df34ea4783b5bf52d7a019bfe102d4194cad1fe434b2
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2026-01-01T00:00:00-05:00
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Cosmic Himalayas in CROCODILE : Probing the Extreme Quasar Overdensities by Count-in-Cells analysis and Nearest Neighbor Distribution
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arXiv:2512.24966v1 Announce Type: new Abstract: The recently reported Cosmic Himalayas (CH) -- an extreme quasar overdensity at z~2 -- poses an apparent challenge to the Lambda CDM framework, with a reported significance of 16.9-sigma under Gaussian assumptions. Such an event appears improbably rare, with a formal probability of P ~ 10^-68. In this work, we investigate whether CH-like structures can naturally arise in cosmological hydrodynamic simulations. Using the CROCODILE simulation, which self-consistently models galaxy-black hole coevolution, we examine quasar clustering through two complementary approaches: the count-in-cells (CIC) statistic, which probes large-scale overdensities, and the nearest-neighbor distribution (NND), sensitive to small-scale environments. CIC analysis reveals that the underlying distribution is heavy-tailed and non-Gaussian, and that conventional Gaussian-based evaluation substantially overestimates the significance of extreme events. When modeled with an asymmetric generalized normal distribution (AGND), the inferred rarity of the CH is substantially reduced and reconciled with standard Lambda CDM; for instance, regions appearing as 12-sigma outliers under Gaussian assumptions (P ~ 10^-33) are found to occur in the AGND regime with a probability of P ~ 10^-4. NND analysis further demonstrates that extreme overdense regions within the simulation can naturally sustain two-point correlation function values similar to those observed in the CH (r0 ~ 30 Mpc/h), suggesting that the strong clustering stems from sample selection biases and local environmental variations. These two analyses conclusively highlight the importance of adopting non-Gaussian statistics when quantifying extreme overdensities of quasars and establish that the CH is not an anomaly, but a natural outcome of structure formation in the Lambda CDM universe.
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https://arxiv.org/abs/2512.24966
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043cecca1c3e9589289d3e54ce45933a431ce49ff78c7edd98afa6ad30c0c655
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2026-01-01T00:00:00-05:00
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Multi-Frequency Study of FRB20201124A with the uGMRT
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arXiv:2512.24978v1 Announce Type: new Abstract: We present results from multi-epoch observations of the repeating fast radio burst FRB 20201124A with the upgraded Giant Metrewave Radio Telescope (uGMRT) during its active phase between 8 May and 28 May 2021. The bursts exhibit significant morphological diversity, including multiple sub-bursts, downward frequency drifts, and intrinsic widths ranging from 1.032 - 32.159 ms. Bursts were detected in both Band 4 (550 - 950 MHz) and Band 5 (1060 - 1460 MHz), with the last Band 5 burst occurring on 24 May, while Band 4 activity persisted until 28 May, indicating a frequency-dependent decline. Consecutive bursts were observed with separations of 16.7 - 291.5 ms, revealing short repetition intervals or potential sub-second quasi-periodicity. The waiting-time and energy distributions are bimodal, suggesting at least two distinct emission timescales and energy modes. Burst fluence ranges from 1.72 - 78.47 Jy ms, and the cumulative fluence distribution follows a broken power law. Multi-frequency analysis further shows closely spaced burst pairs across Band 4 and Band 5, with sub-second offsets of 1.08 - 1.15 s, and no strict simultaneity with contemporaneous FAST detections. These findings demonstrate that FRB 20201124A exhibits closely spaced, patchy, multi-frequency emission with frequency-dependent activity, highlighting the complex and dynamic nature of repeating FRBs.
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https://arxiv.org/abs/2512.24978
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e50038788db38a7b59deb59ffc7af99d7f240b2f5764dba606d3a9691f14ad1b
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2026-01-01T00:00:00-05:00
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Distributions of wide binary stars in theory and in Gaia data: III. Orbital momenta, masses, and manifestations of MOND
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arXiv:2512.25002v1 Announce Type: new Abstract: Using the censored catalog of 103,169 resolved Gaia DR3 binary stars with accurate astrometric data for each component, a new observable, object-specific parameter is computed for each pair: the projected orbital momentum. This parameter is the product of four functions of physical characteristics: total mass, semimajor axis, eccentricity, and inclination angle. Using the previously estimated marginal probability densities of eccentricity and semimajor axis, and assuming an isotropic orientation of binary systems, the sample distribution of mass was adjusted using a concordance metric of the observed and synthetic distributions of orbital momenta and an ad hoc functional model. The best-fitting mass density model is found to faithfully reproduce the observed dependence of orbital momenta on apparent separation, although the absolute luminosity distributions indicate a tendency of the widest systems to more frequently include solar-type primaries. The anticipated manifestation of MOND is computed in the investigated parameter space \{separation, momentum\}. This effect is absent in the given data. The median total mass of the widest Gaia binaries is found to be somewhat higher than that of the tighter pairs, which is interpreted as a dynamical age effect.
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https://arxiv.org/abs/2512.25002
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9c6eec07865050261b8239f349b2ef6d6c4cdf05ed6aa954092bbc79cd9676bf
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2026-01-01T00:00:00-05:00
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Towards precision cosmology with Voids x CMB correlations (I): Roman-Agora mock catalogs and pipeline validation
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arXiv:2512.25040v1 Announce Type: new Abstract: We construct and validate a set of multi-purpose mock galaxy catalogs designed to capture, to different degrees of accuracy, the main characteristics of the Nancy Grace Roman Space Telescope survey. These catalogs provide a foundation for void statistics and various CMB cross-correlation analyses. Our approach differs from traditional halo occupation or abundance matching methods by directly translating a reference mock catalog -- containing basic properties of the host halos -- into a new simulation (in our case Agora). This technique, which we call analog matching, assigns a halo counterpart in the new simulation to each reference galaxy through a nearest-neighbor search in a multi-dimensional parameter space. This space can include halo mass, environmental measures and other galaxy-specific attributes. By varying the composition of this parameter vector, we can generate catalogs of differing complexity and conduct systematic tests to examine the influence of modelling choices on LSS statistics. We find that analog matching based on halo mass alone, or halo mass and galaxy-type indicators, successfully reproduces the expected Roman emission-line galaxy statistics. We also show that reproducing two-dimensional galaxy clustering does not guarantee consistent void properties. Our results highlight the importance of matching void statistics for improved mock accuracy, and demonstrate that measuring voids provides independent and sensitive constraints on galaxy-halo connections beyond the matter power spectrum. An important by-product of our setup is that it is fully general and can be applied to any combination of simulation and reference catalog, provided that the desired parameter space for both is specified. The resulting Roman-Agora mock catalogs offer a versatile resource for LSS x CMB studies and a benchmark for assessing the impact of mock accuracy on cosmological observables.
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https://arxiv.org/abs/2512.25040
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7e55c661e3183c0f6e662aeb010002b0429b7c3eafd2ee2b259d56ba3019dd50
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2026-01-01T00:00:00-05:00
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Feeling Blue: Constructing a Robust SALT3 UV Template and Constraining its Redshift Dependency
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arXiv:2512.25064v1 Announce Type: new Abstract: Upcoming cosmological surveys will obtain numerous rest-frame ultraviolet (UV) observations of Type Ia supernovae (SNe Ia), yet there is concern about how standardizable SNe Ia are in the UV. In this work, we train a robust optical--UV SED model for SNe Ia (SALT3-UV) with the open-source model-training software $\texttt{SALTshaker}$. We incorporate a spectroscopic UV data sample from HST, including 67 UV spectra from 18 nearby SNe Ia. Unlike previous training spectra, the HST spectra have sufficiently precise calibration that they do not require additional warping to match coincident photometric data. Additionally, while including this new SN Ia sample necessitates incorporating auxiliary photometric data from ZTF and ATLAS that have insufficient calibration for cosmological analyses, the improvements in the calibration of these data is anticipated in the near future. Compared to the previous SALT3-K21 model, the SALT3-UV model shows a significant improvement in the UV down to $2000\mathring{\text{A}}$, with over a threefold improvement in model uncertainty and a more physically accurate continuum and line features. We further evaluate potential redshift evolution in the UV template by separating the UV training sample into low- and high-$z$ subsamples. Our results reveal a non-negligible $\gtrsim 0.05$ mag difference between low- and high-$z$ SALT3-UV models in the $g-$band at $z\gtrsim0.5$ and the $u-$band at $z\gtrsim0.2$. We demonstrate that, if confirmed, such evolution could lead to a few-percent bias in the measurement of $w$ if high-$z$ rest-frame UV data are included in future cosmological surveys such as LSST and $\textit{Roman}$.
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https://arxiv.org/abs/2512.25064
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7e5e86382600cdfc15483f7dcf05d8c6cc991f4841cda46136233b647d4d69ff
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2026-01-01T00:00:00-05:00
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Strongly Coupled Sectors in Inflation: Gapped Theories of Unparticles
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arXiv:2512.23796v1 Announce Type: cross Abstract: We consider a novel scenario for a strongly coupled spectator sector during inflation, that of a higher dimensional conformal field theory with large anomalous dimensions -- ``unparticles" -- and compactify the extra dimensions. More specifically, we take generalized free fields in five dimensions, where the extra dimension is compactified to a circle. Due to the usual Kaluza-Klein mechanism, the resulting excitations carry properties of both particles and unparticles, so we dub this scenario ``gapped unparticles". We derive a two-point function of the gapped unparticles by performing dimensional reduction. We then compute, in the collapsed limit, the four-point correlation function of conformally coupled scalars exchanging a gapped unparticle, which are used as seed functions to obtain the correlation function of primordial density perturbations. The phenomenology of the resulting correlators presents some novel features, such as oscillations with an envelope controlled by the anomalous dimension, rather than the usual value of 3/2. Depending on the value of the five-dimensional scaling dimension and effective mass of the gapped unparticles, we find a clear strategy to distinguish gapped unparticles from heavy massive scalars. If we assume the interactions are localized on a brane, gapped unparticles with different effective masses will share a universal coupling, and their exchanges produce an interesting interference pattern.
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https://arxiv.org/abs/2512.23796
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ee4ed1ea6e201a87ec365245bce3a3dbd5dcc862cfe0c8b5169070abdab39b11
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2026-01-01T00:00:00-05:00
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Inflationary QCD phase diagram
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arXiv:2512.24024v1 Announce Type: cross Abstract: Motivated by the cosmological collider program, which aims to probe high-energy physics through inflation, we investigate the phase diagram of multi-flavor QCD in de Sitter spacetime with a flavor-universal axial chemical potential induced by a rolling inflaton coupled to fermions. We determine the first-order critical line and a critical point as functions of the Hubble parameter and the axial chemical potential, employing an effective description of chiral symmetry breaking within the framework of the Nambu--Jona-Lasinio model. We find that a first-order chiral phase transition may occur during inflation or at its end when the axial chemical potential is sufficiently large and crosses the critical line. This provides a cosmological collider analogue of the QCD phase diagram explored in heavy-ion colliders.
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https://arxiv.org/abs/2512.24024
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90c7ea08ee6982d5d61d2404a4aa42f5193f1b543974da47f395095e2225a24c
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2026-01-01T00:00:00-05:00
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Kinematic Anisotropies in PTA Observations: Analytical Toolkit
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arXiv:2512.24055v1 Announce Type: cross Abstract: The reported evidence for an isotropic gravitational-wave background (GWB) from pulsar timing array (PTA) collaborations has motivated searches for extrinsic and intrinsic anisotropies. Kinematic anisotropies may arise as a consequence of a boosted observer moving with respect to the frame in which the GWB appears isotropic. In this work, we present an analytical toolbox to describe the effects of kinematic anisotropies on the overlap reduction function. Our analytical results differ from previous findings at the quadrupole order and are detailed in three appendices. For the first time, we also derive the corresponding auto-correlation using two approaches, taking the pulsar distances to be infinite or finite, respectively. Our formulas can be used in forecasts or Bayesian analysis pipelines.
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https://arxiv.org/abs/2512.24055
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a000b4b326c04dca3ecd350379a22b29349c72387ddf480b92b5b9a9384e74b9
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2026-01-01T00:00:00-05:00
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Sommerfeld Enhancement from Background Force and the Galactic Center GeV Excess
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arXiv:2512.24188v1 Announce Type: cross Abstract: We study the impact of background-induced forces on dark matter (DM) annihilation and their implications for indirect detection. In the presence of a finite number density of background particles, loop-level interactions can generate an effective force that is significantly enhanced relative to the vacuum case. We construct a two-component DM model in which the dominant component is a fermionic particle $\chi$ and the subdominant component is an ultralight pseudoscalar particle $\phi$. The annihilation of $\chi$ proceeds through the p-wave channel and produces gamma-ray emission. The finite density of $\phi$ particles induces a background-enhanced force between $\chi$ particles, leading to a sizable Sommerfeld enhancement of the annihilation. We show that a viable region of parameter space in this model can account for the gamma-ray excess observed in the Galactic Center using Fermi-LAT data. The background-induced force substantially amplifies the Sommerfeld enhancement and thus enlarges the parameter space capable of explaining the excess, highlighting the importance of background effects in astrophysical environments.
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https://arxiv.org/abs/2512.24188
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4656eaa03e0db8802f44ae481540e273dfe937be18bd890ded0e63d6f0187fa1
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2026-01-01T00:00:00-05:00
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Impact of Anisotropy on Neutron Star Structure and Curvature
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arXiv:2512.24194v1 Announce Type: cross Abstract: We investigate the impact of pressure anisotropy on the structural and geometric properties of neutron stars within general relativity, focusing primarily on the phenomenological Bowers-Liang (BL) model, and comparing selected results with a quasi-local prescription. Using the SLy equation of state, we explore how anisotropic stresses modify global observables such as the mass-radius relation, moment of inertia, compactness, and tidal deformability over a broad range of anisotropy parameters. We find that moderate positive anisotropy can increase the maximum supported mass up to approximately $2.4\;M_\odot$ and enhance stellar compactness by up to $20\%$ relative to isotropic configurations, while remaining broadly consistent with current NICER and gravitational-wave constraints. To probe the internal gravitational field, we compute curvature invariants including the Ricci scalar, the Ricci tensor contraction, the Kretschmann scalar, and the Weyl scalar. We show that curvature measures directly tied to the matter distribution exhibit a strong sensitivity to anisotropy, whereas the Weyl curvature remains comparatively insensitive, reflecting its role as a measure of the free gravitational field. Within the phenomenological BL framework, the maximum compactness increases with anisotropy and reaches values as high as $\mathcal{C}_{\max}\approx 0.25$-$0.38$ for $\lambda_{\rm BL}\in[-4,+4]$, although the physical realizability of such highly compact configurations depends sensitively on the underlying anisotropy mechanism. A comparison with the quasi-local model highlights the strong model dependence of anisotropic effects, underscoring both the potential significance and the limitations of phenomenological anisotropy prescriptions in modeling strong-field neutron-star interiors.
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https://arxiv.org/abs/2512.24194
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b2cafeaca710a7e72220d049d30a16766d93b32fb2049e9827b4b9be8b1ac2d4
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2026-01-01T00:00:00-05:00
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Big Bang Nucleosynthesis results refined via the Trojan Horse Method
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arXiv:2512.24358v1 Announce Type: cross Abstract: This work presents the Trojan Horse Method (THM) as a powerful technique for measuring nuclear reaction cross sections at astrophysical energies. We then explore the impact of THM-derived reaction rates on the predictions of Standard Big Bang Nucleosynthesis (SBBN) using the PRIMAT code. Primordial abundances are shown for the single rate impact and, for the first time, also for all the THM rates together. The result shows significant differences with the use of THM rates, which in some cases goes in the direction of improving the agreement with the observations with respect to the use of only reaction rates from direct data, especially for the $^7$Li and deuterium abundances, which are still open issues for SBBN.
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https://arxiv.org/abs/2512.24358
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bc34a181b2674ae8491d0bf9c29ac9edac8cdd357ea049136f138b38ee6f1fd3
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2026-01-01T00:00:00-05:00
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Memories of Prof. George Lazarides
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arXiv:2512.24481v1 Announce Type: cross Abstract: I present some memories of my Ph.D supervisor and, later, collaborator but always encouraging supporter Prof. G. Lazarides. Some of his contributions to our common and related scientific activities on the phenomenology of MSSM and inflation are also summarized.
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https://arxiv.org/abs/2512.24481
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bf1acf47f258f4c284b6eb322404de9eec58d12044ec31f35e1bdce46ced21f1
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2026-01-01T00:00:00-05:00
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Higgs-like inflation in scalar-torsion $f(T,\phi)$ gravity in light of ACT-SPT-DESI constraints
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arXiv:2512.24502v1 Announce Type: cross Abstract: We study Higgs-like inflation in the framework of scalar-torsion gravity, focusing on the general class of $f(T,\phi)$ theories in which gravitation is mediated by torsion rather than curvature. Motivated by the increasing precision of cosmic microwave background and large-scale-structure observations, we examine whether Higgs-like inflation remains compatible with current data in this extended gravitational setting. Working within the slow-roll approximation, we analyze the inflationary dynamics both analytically and numerically. In the dominant-coupling regime we derive closed-form expressions for the scalar spectral index and the tensor-to-scalar ratio as functions of the number of e-folds, and we subsequently relax this assumption by numerically solving the slow-roll equations. Confrontation with the latest constraints from Planck 2018, ACT DR6, DESI DR1, and BICEP/Keck shows that Higgs-like inflation in $f(T,\phi)$ gravity is fully consistent with current bounds, naturally accommodating the preferred shift in the scalar spectral index and leading to distinctive tensor-sector signatures.
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https://arxiv.org/abs/2512.24502
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b91213947fc00566505b8c428fc184133eed57a8a03788f3953c65930988de13
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2026-01-01T00:00:00-05:00
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Stellar modeling within regularized 4D Einstein-Gauss-Bonnet gravity in light of current astrophysical constraints
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arXiv:2512.24554v1 Announce Type: cross Abstract: In this study we obtain interior solutions and investigate structural properties of isotropic compact stars in the framework of four-dimensional regularized Einstein-Gauss-Bonnet (4DEGB) gravity. For stellar matter content, we adopt a widely used quark-matter model that approximates a realistic equation of state (EoS). By numerically integrating the modified Tolman-Oppenheimer-Volkoff equations, we obtain interior solutions for static, spherically symmetric fluid spheres. The resulting sequences are compared directly with the predictions of General Relativity (GR). Our analysis focuses on three diagnostic indicators: (i) the mass-radius profiles under GR and three representative choices of the Gauss-Bonnet coupling; (ii) the stellar compactness factor, $C \equiv M/R$; and (iii) the relation between stellar mass and central energy density. Recent observational studies suggest that the maximum masses inferred from the mass-radius relation may be larger than previously expected. To address this, we include a comparative set of constraints from multi-messenger astrophysical observations, including gravitational-wave event GW190814, as well as X-ray measurements from NICER for PSR~J0740+6620 and PSR~J0030+0451. These data provide stringent, astrophysically grounded tests of the viability of the models discussed here. Our results indicate that compact stars within 4DEGB gravity are systematically less compact and achieve moderately higher maximum masses compared to the GR case. This trend is consistent with recent theoretical analyses of compact stars in higher-curvature gravity theories and with constraints from multi-messenger astrophysics. Together, these findings suggest that regularized Gauss-Bonnet corrections constitute a plausible extension of GR in the strong-field regime.
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https://arxiv.org/abs/2512.24554
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6c10530363ceeddeeb538e7d24325892157934b1f2852e5aefc2d0d2bfad61ec
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2026-01-01T00:00:00-05:00
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Aspects of Sommerfeld Enhancement in the light of Halo gamma-ray excess
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arXiv:2512.24662v1 Announce Type: cross Abstract: We examine Sommerfeld enhancement in dark matter annihilation as a potential origin of the halo-like gamma-ray excess near $E_\gamma \simeq 20$ GeV reported by Totani. A minimal model with a light CP-even scalar mediator naturally produces a velocity-dependent annihilation cross section consistent with thermal freeze-out, the Milky Way excess, and limits from dwarf spheroidal galaxies.
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https://arxiv.org/abs/2512.24662
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e60de436f31e4ae2d430b4d07748b7b0c3c4d2948fd6ff68cd94c5af3ffeb4d2
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2026-01-01T00:00:00-05:00
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Difference between quark stars and neutron stars in universal relations and their effect on gravitational waves
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arXiv:2512.24703v1 Announce Type: cross Abstract: We calculate the $f$-mode frequency and tidal overlap of quark stars using the full general relativity method. We verify the universal relations obtained from conventional neutron stars in the case of quark stars and explore the cases with different values of parameters of the quark star equation of state. Since quark stars have significantly smaller radii compared to neutron stars in the low mass range, the relation between the tidal defomability and $f$-mode frequency times radius is different for neutron stars and quark stars. This difference has an impact on dynamical tide, which is the lowest-order effect we know of that can distinguish quark stars and neutron stars from the gravitational wave during the inspiral phase. We calculate the tidal dephasing caused by this effect in the post-Newtonian method and find that it can not be detected even by the next-generation gravitational wave detectors.
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https://arxiv.org/abs/2512.24703
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333dd048dcb4f4b330eaa5201230ff3ee4f2d60cf9c4c82dcf571862aac1397e
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2026-01-01T00:00:00-05:00
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Model-independent search of gravitational wave echoes in LVK data
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arXiv:2512.24730v1 Announce Type: cross Abstract: Gravitational wave echoes offer a unique probe of the near-horizon structure of astrophysical black holes, beyond the standard ''black hole spectroscopy''. Theoretical waveform predictions, however, remain uncertain, motivating robust searches that avoid specific echo modeling. We present a model-independent search framework targeting long-lived quasinormal modes (QNMs) expected from strong interior reflection. By employing a generalized phase-marginalized likelihood that coherently combines data for each QNM across a detector network, our method enhances sensitivity to the signals. To handle real detector noise, we implement an optimized notching procedure to suppress instrumental spectral lines and refine the Bayesian parameter settings. We validate the performance of this framework using injection studies on O1 background data, demonstrating reliable signal recovery in realistic noise conditions. We then apply this method to three binary black hole merger events with high ringdown signal-to-noise ratios (SNR) from observing runs O1 to O4: GW150914, GW231226, and the recently detected GW250114. No statistically significant evidence for postmerger echoes is found. Consequently, we derive 90% upper limits on the network SNR and the average amplitude of the long-lived QNMs, setting the first model-independent constraints on late-time echo signatures from LVK data.
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https://arxiv.org/abs/2512.24730
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fc1ba0c6d490580348821e67e7f136f0ddd90876c07c47742a489f4f8dcff966
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2026-01-01T00:00:00-05:00
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Loop-Level Lepton Flavor Violation and Diphoton Signals in the Minimal Left-Right Symmetric Model
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arXiv:2512.25019v1 Announce Type: cross Abstract: The left-right symmetric model (LRSM) could not only restore parity of the weak interaction, but also provide natural explanations of the tiny active neutrino masses via the seesaw mechanisms. The $SU(2)_R$-breaking scalar $H_3$ can induce lepton flavor violating (LFV) effects in the minimal version of LRSM at the 1-loop order, originating from the mixing of heavy right-handed neutrinos. If $H_3$ is light, say below the GeV scale, it will lead to rich signals, e.g. the LFV muon and tauon decays $\ell_\beta \to \ell_\alpha + X$ ($X$ being either visible or invisible final states) and the anomalous supernova signatures. Combined with the diphoton coupling of $H_3$, the right-handed scale $v_R$ is excluded up to $2\times10^9$ GeV. In the future, the $v_R$ scale can be probed up to $5\times10^9$ GeV in high-precision muon experiments, and further up to $6\times10^{11}$ GeV by supernova observations.
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https://arxiv.org/abs/2512.25019
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d8e5728c36c191a2f6752f27092809543ab2cf9560a67c51dc8676995f2173a0
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2026-01-01T00:00:00-05:00
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Primordial black hole dark matter from ultra-slow-roll inflation in Horndeski gravity
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arXiv:2512.25044v1 Announce Type: cross Abstract: Primordial black holes (PBHs) provide a well-motivated non-particle candidate for dark matter, requiring an enhancement of curvature perturbations on small inflationary scales consistent with observational constraints. In this work we study PBH production within Horndeski gravity, accounting for compatibility with the GW170817 constraint on the gravitational-wave speed and imposing a constant coupling to the Ricci scalar. Under these conditions, and assuming an inflaton field characterised by a canonical kinetic term and a smooth potential, the inflationary dynamics is controlled by the cubic Horndeski interaction. We show that a suitable kinetic dependence of the latter enhances the effective friction acting on the inflaton, inducing a transient ultra-slow-roll phase embedded in an otherwise standard slow-roll evolution. Interestingly, this mechanism amplifies the curvature power spectrum on small scales without introducing any feature in the potential. For representative parameter choices we find that pronounced peaks in the scalar power spectrum are generated, leading to the formation of asteroid-mass PBHs with masses of order $\mathcal{O}(10^{-16})\,M_\odot$, which can account for a substantial fraction of the dark matter abundance, reaching $f_{\rm PBH}\simeq 0.9$, while satisfying current observational constraints. The resulting sharp features in the scalar power spectrum also imply potentially observable scalar-induced gravitational-wave signatures.
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https://arxiv.org/abs/2512.25044
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af1b07392dff5287ffaf6b6a9babca09d51fb8d72e516ba9b6f3e385e892ffd0
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2026-01-01T00:00:00-05:00
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Effect of Magnetised Discontinuity on Diffusive Shock Acceleration
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arXiv:2401.08969v2 Announce Type: replace Abstract: We investigate the impact of magnetic fields and diffusion mechanisms on the energy spectra of particles accelerated via diffusive shock acceleration. We analyse magnetised shock jump conditions and demonstrate how magnetisation and angular dependence modify upstream and downstream velocities, which enter the transport equation within a Monte Carlo simulation framework. We consider constant, momentum-dependent, and pitch-angle-dependent diffusion coefficients to assess their influence on particle acceleration. Our results show that magnetic fields enhance particle confinement and facilitate more efficient energy gain. In the absence of magnetisation, particle spectra tend to be steeper due to rapid escape and weaker scattering effects, whereas magnetised shocks systematically produce flatter spectra across all diffusion models. Among them, pitch-angle-dependent diffusion leads to the strongest spectral flattening, underscoring its role in sustaining extended acceleration. It is also seen that an increased upstream pressure, associated with enhanced magnetic turbulence, broadens the spectral range by improving particle scattering efficiency and enabling multiple shock crossings. As the shock inclination angle increases, the velocity contrast between upstream and downstream regions diminishes, modulating the spatial extent of the acceleration zone. Notably, pitch-angle-dependent diffusion remains robust under varying shock conditions, ensuring sustained acceleration.
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https://arxiv.org/abs/2401.08969
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a3a4aa693c3747391e0fb4ea7afc3146ab9adf26b7829ab1d061fea1ed9f8bb6
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2026-01-01T00:00:00-05:00
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Observation of the $\gamma$-ray Emission from W43 with LHAASO
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arXiv:2408.09905v2 Announce Type: replace Abstract: In this paper, we report the detection of the very-high-energy (VHE, $ 100{\rm\ GeV} 100\rm\ TeV$) $\gamma$-ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended $\gamma$-ray source was detected with a significance of ${\sim}16\,\sigma$ by KM2A and ${\sim}17\,\sigma$ by WCDA, respectively. The angular extension of this $\gamma$-ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the $\gamma$-ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.
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https://arxiv.org/abs/2408.09905
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e469e8cef417f670e655d14d2452b00fb9da9c89ef2303fc26e3c7acb56aeb4c
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2026-01-01T00:00:00-05:00
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Deep view of Composite SNR CTA1 with LHAASO in $\gamma$-rays up to 300 TeV
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arXiv:2409.09499v2 Announce Type: replace Abstract: The ultra-high-energy (UHE) gamma-ray source 1LHAASO J0007+7303u is positionally associated with the composite SNR CTA1 that is located at high Galactic Latitude $b\approx 10.5^\circ$. This provides a rare opportunity to spatially resolve the component of the pulsar wind nebula (PWN) and supernova remnant (SNR) at UHE. This paper conducted a dedicated data analysis of 1LHAASO J0007+7303u using the data collected from December 2019 to July 2023. This source is well detected with significances of 21$\sigma$ and 17$\sigma$ at 8$-$100 TeV and $>$100 TeV, respectively. The corresponding extensions are determined to be 0.23$^{\circ}\pm$0.03$^{\circ}$ and 0.17$^{\circ}\pm$0.03$^{\circ}$. The emission is proposed to originate from the relativistic electrons and positrons accelerated within the PWN of PSR J0007+7303. The energy spectrum is well described by a power-law with an exponential cutoff function $dN/dE = (42.4\pm4.1)(\frac{E}{20\rm\ TeV})^{-2.31\pm0.11}\exp(-\frac{E}{110\pm25\rm\ TeV})$ $\rm\ TeV^{-1}\ cm^{-2}\ s^{-1}$in the energy range from 8 TeV to 300 TeV, implying a steady-state parent electron spectrum $dN_e/dE_e\propto (\frac{E_e}{100\rm\ TeV})^{-3.13\pm0.16}\exp[(\frac{-E_e}{373\pm70\rm\ TeV})^2]$ at energies above $\approx 50 \rm\ TeV$. The cutoff energy of the electron spectrum is roughly equal to the expected current maximum energy of particles accelerated at the PWN terminal shock. Combining the X-ray and gamma-ray emission, the current space-averaged magnetic field can be limited to $\approx 4.5\rm\ \mu G$. To satisfy the multi-wavelength spectrum and the $\gamma$-ray extensions, the transport of relativistic particles within the PWN is likely dominated by the advection process under the free-expansion phase assumption.
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https://arxiv.org/abs/2409.09499
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09225089b0631d8f78379d226f0c81b68f1961b4a4e0f8fb154099e6a5afec25
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2026-01-01T00:00:00-05:00
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RHINO: A large horn antenna for detecting the 21cm global signal
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arXiv:2410.00076v2 Announce Type: replace Abstract: The sky-averaged brightness temperature of the 21cm line from neutral hydrogen provides a sensitive probe of the thermal state of the intergalactic medium, particularly before and during Cosmic Dawn and the Epoch of Reionisation. This `global signal' is faint, on the order of tens to hundreds of millikelvin, and spectrally relatively smooth, making it exceedingly difficult to disentangle from foreground radio emission and instrumental artefacts. In this paper, we introduce RHINO, an experiment based around a large horn antenna operating from 60-85 MHz. Horn antennas are highly characterisable and provide excellent shielding from their immediate environment, which are potentially decisive advantages when it comes to the beam measurement and modelling problems that are particularly challenging for this kind of experiment. The system also includes a novel continuous wave calibration source to control correlated gain fluctuations, allowing continuous monitoring of the overall gain level without needing to rapidly switch between the sky and a calibration source. Here, we describe the basic RHINO concept, including the antenna design, EM simulations, and receiver electronics. We use a basic simulation and analysis pipeline to study the impact of the limited bandwidth on recovery of physical 21cm global signal model parameters, and discuss a basic calibration scheme that incorporates the continuous wave signal. Finally, we report on the current state of a scaled-down prototype system under construction at Jodrell Bank Observatory.
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https://arxiv.org/abs/2410.00076
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59a469a2a308c771c3a7a58eaa04ec0547b6ed5184ccb7cfcf779a2adf16ee45
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2026-01-01T00:00:00-05:00
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Unraveling the Nature of HAWC J1844-034 with Fermi-LAT Data Analysis and Multi-wavelength Modeling
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arXiv:2501.12065v2 Announce Type: replace Abstract: The extended ultra-high-energy (UHE) gamma-ray source HAWC J1844-034 is closely associated with two other sources, HAWC J1843-032 and HWC J1846-025. Moreover, other gamma-ray observatories like H.E.S.S., LHAASO, and Tibet AS$_{\gamma}$ have detected UHE gamma-ray sources whose spatial positions coincide with the position of HAWC J1844-034. The UHE gamma-ray data from several observatories help analyse the spectral features of this source in detail at TeV energies. Of the four pulsars near HAWC J1844-034, PSR J1844-0346 is closest to it and possibly supplies the cosmic-ray leptons to power this source. We have analysed the Fermi-LAT data to explore this source's morphology and identify its spectral feature in the Fermi-LAT energy band. After removing the contribution of the pulsar to the gamma-ray spectral energy distribution by pulsar phased analysis, we have obtained upper limits on the photon flux and identified the GeV counterpart PS J1844.2-0342 in the Fermi-LAT energy band with more than 5$\sigma$ significance, which may be a pulsar wind nebula (PWN). Finally, the multi-wavelength spectral energy distribution is modeled, assuming HAWC J1844-034 is a PWN.
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https://arxiv.org/abs/2501.12065
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786a1cf8aa9ea72f7adfcb2cddeaf4ed70693edeb707887fdc91e4f5cfa7e4e7
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2026-01-01T00:00:00-05:00
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Gravitational wave probes of particle dark matter: a review
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arXiv:2503.02607v5 Announce Type: replace Abstract: Various theories of dark matter predict distinctive astrophysical signatures in gravitational-wave sources that could be observed by ground- and space-based laser interferometers. Different candidates-including axions, dark photons, macroscopic dark matter, WIMPs, and dark-matter spikes-may appear in interferometer data via their coupling to gravity or the Standard Model, altering the measured gravitational-wave strain in distinct ways. Despite their differences, these candidates share two key features: (1) they can be probed through their effects on gravitational waves from inspiraling compact objects, isolated black holes, and neutron stars, or via direct interactions with detectors, and (2) their signatures likely persist far longer than the seconds-long mergers detected today, necessitating new data analysis methods beyond matched filtering. This review outlines these dark matter candidates, their observational signatures, and approaches for their detection.
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https://arxiv.org/abs/2503.02607
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1de795bd507cd69899e291c0dc12bfcaa8541d6c8428a3d641d607d7fee76b98
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2026-01-01T00:00:00-05:00
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NLTE spectral modelling for a carbon-oxygen and helium white-dwarf merger as a Ca-rich transient candidate
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arXiv:2503.12105v2 Announce Type: replace Abstract: We carry out NLTE (non local thermodynamic equilibrium) radiative transfer simulations to determine whether explosion during the merger of a carbon-oxygen (CO) white dwarf (WD) with a helium (He) WD can reproduce the characteristic Ca II/[Ca II] and He I lines observed in Ca-rich transients. Our study is based on a 1D representation of a hydrodynamic simulation of a 0.6 $M_{\odot}$ CO + 0.4 $M_{\odot}$ He WD merger. We calculate both photospheric and nebular-phase spectra including treatment for non-thermal electrons, as is required for accurate modelling of He I and [Ca II]. Consistent with Ca-rich transients, our simulation predicts a nebular spectrum dominated by emission from [Ca II] 7291, 7324 angstrom and the Ca II near-infrared (NIR) triplet. The photospheric-phase synthetic spectrum also exhibits a strong Ca II NIR triplet, prominent optical absorption due to He I 5876 angstrom and He I 10830 angstrom in the NIR, as is commonly observed for Ca-rich transients. Overall, our results therefore suggest that CO+He WD mergers are a promising channel for Ca-rich transients. However, the current simulation overpredicts some He I features, in particular both He I 6678 and 7065 angstrom and shows a significant contribution from Ti II, which results in a spectral energy distribution that is substantially redder than most Ca-rich transients at peak. Additionally the Ca II nebular emission features are too broad. Future work should investigate if these discrepancies can be resolved by considering full 3D models and exploring a range of CO+He WD binary configurations.
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https://arxiv.org/abs/2503.12105
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c3307033454c0b0189822a9fd17a6e5df22e9b28f217e2e6fb1c6885dc4d4869
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2026-01-01T00:00:00-05:00
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Study of Ultra-High-Energy Gamma-Ray Source 1LHAASO J0056+6346u and Its Possible Origins
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arXiv:2504.00601v2 Announce Type: replace Abstract: We report a dedicated study of the newly discovered extended UHE $\gamma$-ray source 1LHAASO J0056+6346u. Analyzing 979 days of LHAASO-WCDA data and 1389 days of LHAASO-KM2A data, we observed a significant excess of $\gamma$-ray events with both WCDA and KM2A. Assuming a point power-law source with a fixed spectral index, the significance maps reveal excesses of ${\sim}12.65\,\sigma$, ${\sim}22.18\,\sigma$, and ${\sim}10.24\,\sigma$ in the energy ranges of 1--25 TeV, 25--100 TeV, and $> 100$ TeV, respectively. We use a 3D likelihood algorithm to derive the morphological and spectral parameters, and the source is detected with significances of $12.65\,\sigma$ by WCDA and $25.27\,\sigma$ by KM2A. The best-fit positions derived from WCDA and KM2A data are (R.A. = $13.96^\circ\pm0.09^\circ$, Decl. = $63.92^\circ\pm0.05^\circ$) and (R.A. = $14.00^\circ\pm0.05^\circ$, Decl. = $63.79^\circ\pm0.02^\circ$), respectively. The angular size ($r_{39}$) of 1LHAASO J0056+6346u is $0.34^\circ\pm0.04^\circ$ at 1--25 TeV and $0.24^\circ\pm0.02^\circ$ at $> 25$ TeV. The differential flux of this UHE $\gamma$-ray source can be described by an exponential cutoff power-law function: $(2.67\pm0.25) \times 10^{-15} (E/20\,\text{TeV})^{-1.97\pm0.10} e^{-E/(55.1\pm7.2)\,\text{TeV}} \,\text{TeV}^{-1}\,\text{cm}^{-2}\,\text{s}^{-1}$. To explore potential sources of $\gamma$-ray emission, we investigated the gas distribution around 1LHAASO J0056+6346u. 1LHAASO J0056+6346u is likely to be a TeV PWN powered by an unknown pulsar, which would naturally explain both its spatial and spectral properties. Another explanation is that this UHE $\gamma$-ray source might be associated with gas content illuminated by a nearby CR accelerator, possibly the SNR candidate G124.0+1.4.
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https://arxiv.org/abs/2504.00601
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4901baa741a6b37de63cfc2b17f2fcf1a1d4ad0fa97c7112fcd66b905089e6fa
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2026-01-01T00:00:00-05:00
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Constraining Lens Masses in Moderately to Highly Magnified Microlensing Events from Gaia
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arXiv:2504.11546v2 Announce Type: replace Abstract: Microlensing events provide a unique way to detect and measure the masses of isolated, non-luminous objects, particularly dark stellar remnants. Under certain conditions, it is possible to measure the mass of these objects using photometry alone, specifically when a microlensing light curve displays a finite source (FS) effect. This effect generally occurs in highly magnified light curves, i.e. when the source and the lens are very well aligned. In this study, we analyse Gaia Alerts and Gaia Data Release 3 datasets, identifying four moderate-to-high-magnification microlensing events without a discernible FS effect. The absence of this effect suggests a large Einstein radius, implying substantial lens masses. In each event, we constrained the FS effect, and therefore established lower limits for the angular Einstein radius and lens mass. Additionally, we used the DarkLensCode software to obtain the mass, distance, and brightness distribution for the lens based on the Galactic model. Our analysis established lower mass limits of $\sim 0.7$ $M_{\odot}$ for one lens and $\sim 0.3-0.5$ $M_{\odot}$ for two others. A DarkLensCode analysis supports these findings, estimating lens masses in the range of $\sim 0.42-1.70$ $M_{\odot}$ and dark lens probabilities exceeding 80%. These results strongly indicate that the lenses are stellar remnants, such as white dwarfs or neutron stars. While further investigations are required to confirm the nature of these lenses, we demonstrate a straightforward yet effective approach to identifying stellar remnant candidates.
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https://arxiv.org/abs/2504.11546
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5f16fcb19e56eeaa00bb7e5eac180316375b318271e6fa950fb0d5b601de15a8
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2026-01-01T00:00:00-05:00
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Intermediate-mass black holes and contribution to extragalactic background light from Population III stars in Milky Way-like galaxies
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arXiv:2505.02245v2 Announce Type: replace Abstract: The mass range of observed black holes extends from stellar-mass to supermassive scales, yet the existence of objects in the intermediate-mass range of $10^{2} - 10^{5} \text{M}_{\odot}$ remains unconfirmed. Black holes are suspected to compress the surrounding dark matter distribution, forming a ``spike''. If dark matter is self-annihilating, the spike could produce gamma-ray emission sufficiently luminous to be detected. This work aims to estimate the number of expected unmerged intermediate-mass black holes in a Milky Way-like galaxy that could form such spikes. These intermediate-mass black holes are assumed to have formed from the collapse of high-mass Population III stars, such that the resulting merger rate is constrained by observations of gravitational wave emission. It is furthermore estimated to what extent the progenitor Population III stars contribute to the extragalactic background light. The Population III stars are simulated and tracked using the A-SLOTH semi-analytical simulation code and the resulting number of intermediate-mass black holes is constrained by applying the Population III binary black hole merger rate to an effective volume determined from the Population III star formation rate. In this framework, $\sim 130$ unmerged IMBHs from Population III stars are expected to reside in a Milky Way-like galaxy. The contribution of their progenitors to the extragalactic background light in the near-infrared is less than $10^{-3} \text{nW} \text{m}^{-2} \text{sr}^{-1}$, well below previous estimates.
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https://arxiv.org/abs/2505.02245
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8965cc36d691c1f783593e156d59599eab82ecbc17a045af8f301ceea7bf0ca8
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2026-01-01T00:00:00-05:00
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When Dark Matter Heats Up: A Model-Independent Search for Non-Cold Behavior
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arXiv:2505.09470v2 Announce Type: replace Abstract: This article questions the common assumption of cold dark matter (DM) by exploring the possibility of a non-zero equation of state (EoS) without relying on any parametric approach. In standard cosmological analyses, DM is typically modeled as pressureless dust with $w_{\rm DM} = 0$, an assumption that aligns with large-scale structure formation, supports the empirical success of the $\Lambda$CDM model, and simplifies cosmological modeling. However, there is no fundamental reason to exclude a non-zero $w_{\rm DM}$ from the cosmological framework. In this work, we explore this possibility through non-parametric and parametric reconstructions based on Gaussian Process Regression. The reconstructions use Hubble parameter measurements from Cosmic Chronometers (CC), the Pantheon+ sample of Type Ia supernovae, and Baryon Acoustic Oscillation (BAO) data from DESI DR1 and DR2. Our findings suggest that a dynamical EoS for DM, although only mildly supported statistically, cannot be conclusively ruled out. Notably, we observe a mild tendency ($\sim 1\sigma$) toward a negative $w_{\rm DM}$ at the present epoch, which is most likely due to inconsistencies between the BAO data from DESI and other datasets.
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https://arxiv.org/abs/2505.09470
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5c9de374652bed6f678bc5c3020605af3b765b16efd9eb3de99850afb09c4788
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2026-01-01T00:00:00-05:00
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Search for Lorentz Invariance Violation with spectral lags of GRB 190114C using profile likelihood
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arXiv:2506.05737v3 Announce Type: replace Abstract: We search for Lorentz invariance violation (LIV) by re-analyzing the spectral lag data for GRB 190114C \rthis{from Fermi-GBM} using frequentist analysis, where we deal with the astrophysical nuisance parameters using profile likelihood. For this use case, we find a global minima for the $\chi^2$ as a function of energy scale of LIV ($E_{QG}$), well below the Planck scale. The best-fit $1\sigma$ central intervals for $E_{QG}$ are given by $2.81^{+0.50}_{-0.37}\times 10^{14}$ GeV and $9.85^{+0.84}_{-0.60}\times 10^{5}$ GeV for linear and quadratic LIV, respectively, and agree with the Bayesian estimates obtained so far in a previous work. Therefore, the results from the frequentist analysis of GRB 190114C agree with Bayesian analysis.
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https://arxiv.org/abs/2506.05737
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28f32d3e80cf39e3e2ea3b72aebd05cf27574deee1020392189b9591830c5a85
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2026-01-01T00:00:00-05:00
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XSPECT on-board XPoSat: Calibration and First Results
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arXiv:2506.09918v2 Announce Type: replace Abstract: XPoSat is India's first X-ray spectro-polarimetry mission, consisting of two co-aligned instruments, a polarimeter (POLIX) and a spectrometer (XSPECT), to study the X-ray emission from celestial sources. Since polarimetry is a photon-hungry technique, the mission is designed to observe sources for long integration times (~ few days to weeks). This provides an unique opportunity, enabling XSPECT to carry out long-term monitoring of sources, and study their spectro-temporal evolution. To ensure that the instrument is able to fulfill its scientific objectives, it was extensively calibrated on-ground. Post launch, these calibrations were validated using on-board observations. Additionally, some aspects of the instrument such as alignment and effective area were also derived and fine-tuned from in-flight data. In this paper, we describe the calibration of XSPECT instrument in detail, including some initial results derived from its data to establish its capabilities.
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https://arxiv.org/abs/2506.09918
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5390bee83d69eca742fcf83e15c84ba328633fbedf18085b31ce939e270537a4
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2026-01-01T00:00:00-05:00
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Kinematic Confirmation of a Remarkable Linear Trail of Galaxies in the NGC 1052 Field, Consistent with Formation in a High-Speed Bullet Dwarf Collision
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arXiv:2506.10220v2 Announce Type: replace Abstract: A unique linear trail of diffuse galaxies was recently identified in the NGC 1052 field. This trail includes the remarkable, ultra-diffuse galaxies DF2 and DF4 which lack dark matter and host unusually luminous globular clusters. It has been proposed that the trail formed via a high-speed collision between two gas-rich dwarf galaxies. This scenario predicts that the trail galaxies are kinematically connected and follow a specific trend in radial velocity as a function of position, based on the known velocities and positions of DF2 and DF4. To test this hypothesis, we measured radial velocities for seven additional galaxies on the trail. While the galaxies' low surface brightnesses presented observational challenges, we employ several methods to obtain measurements for galaxies with effective surface brightnesses up to 28.6 mag arcsec$^{-2}$, including a narrow slit placed over globular clusters and a novel wide slit mode on Keck/LRIS, as well as a 'light bucket' mode on Keck/KCWI. We find that five of our seven targets follow the precise velocity trend predicted by DF2 and DF4, to a degree with just a 2% chance of randomly occurring. Moreover, the trail galaxies' radial velocities are significantly higher than those of the NGC 1052 group, setting it apart as a separate, kinematically connected system. Our findings support the theory that this trail of galaxies, including DF2 and DF4, formed together in a single event. A 'bullet dwarf' collision remains the only known explanation for all the unusual properties of DF2, DF4, and the associated trail of galaxies.
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https://arxiv.org/abs/2506.10220
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965e876e53a99b6fbc5eeb7cf1ee81285a201b77bc2ff7086d1c5b37e65b5ddf
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2026-01-01T00:00:00-05:00
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Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots
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arXiv:2507.12618v3 Announce Type: replace Abstract: The James Webb Space Telescope (JWST) has unveiled a population of enigmatic, compact sources at high redshift known as ``Little Red Dots'' (LRDs), whose physical nature remains a subject of intense debate. Concurrently, the rapid assembly of the first supermassive black holes (SMBHs) requires the formation of heavy seeds, for which supermassive stars (SMSs) are leading theoretical progenitors. In this work, we perform the first quantitative test of the hypothesis that LRDs are the direct observational manifestation of these primordial SMSs. We present a novel, first-principles pipeline generating synthetic spectra for a non-rotating, metal-free SMS up to $10^6 \, M_\odot$. We establish that its luminosity ($L_\lambda \approx 1.7 \times 10^{44} \, \text{erg} \, \text{s}^{-1} \, \mu\text{m}^{-1}$ at 4050\,\AA) provides a decisive constraint, matching prominent LRDs. Our model self-consistently reproduces their defining spectral features: the V-shaped Balmer break morphology is shown to be an intrinsic photospheric effect, while the complex line phenomenology, strong H$\beta$ in emission with other Balmer lines in absorption arises from non-LTE effects in a single stellar atmosphere. With wind and macroturbulent broadening, we match LRD spectra at $z=7.76$ and $z=3.55$, including the H$\beta$ width of MoM-BH*-1 to within 4\%. We predict a luminosity-dependent observability window, $\sim10^{4}$ yr for the most luminous systems and $10^{5}$--$10^{6}$ yr if $L_\lambda(4050\,\text{\AA})$ is lower by 1--2 dex. These results provide a self-consistent alternative to multi-component obscured AGN scenarios and suggest JWST may be witnessing luminous stages of SMBH progenitors before collapse.
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https://arxiv.org/abs/2507.12618
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cc68356aeb564aa7399ad830a289d37067e5abd5dcdbc8d7c96b1a66ca5fd624
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2026-01-01T00:00:00-05:00
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Growth Index in the $\gamma\delta$CDM model
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arXiv:2508.14749v3 Announce Type: replace Abstract: To better distinguish the nature of $H_0$ and $S_8$ tensions, it is necessary to separate the effects of expansion and the growth of structure. The growth index $\gamma$ was identified as the most important parameter that characterizes the growth of density fluctuations independently of the effects of cosmic expansion. In the $\Lambda$CDM model, analyses performed with various cosmological datasets indicate that the growth index has to be larger than its theoretically predicted value. Cosmological models based on $f(R)$ gravity theories have scale-dependent growth indices, whose values are even more at odds with the growth rate data. In this work, we evaluate the growth index in the $\gamma\delta$CDM model both theoretically and numerically. Although based on $f(R)$ gravity theory, we show through several analyses with different combinations of datasets that the growth index in the $\gamma\delta$CDM model is very close in value to the $\Lambda$CDM and the $\omega$CDM models. The growth of structure is suppressed in the $\gamma\delta$CDM model, which is formulated with the extended gravitational growth framework. Upon analyzing cosmological data, we ascertain that the $\gamma\delta$CDM model is equally competitive as the $\Lambda$CDM and the $\omega$CDM models.
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https://arxiv.org/abs/2508.14749
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5d4b274daec64b73cfb69d54ce2c25d7f8a13893e8f5d5c2b88cecb8af00a778
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2026-01-01T00:00:00-05:00
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Primordial Black Holes Evaporating before Big Bang Nucleosynthesis
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arXiv:2509.05618v2 Announce Type: replace Abstract: Primordial black holes (PBHs) formed from the collapse of density fluctuations provide a unique window into the physics of the early Universe. Their evaporation through Hawking radiation around the epoch of Big Bang nucleosynthesis (BBN) can leave measurable imprints on the primordial light-element abundances. In this work, we analyze in detail the effects of PBHs evaporating before BBN, with various intermediate steps understood analytically, and obtain the BBN constraint on PBHs within a transparent and reproducible framework. We find that, to produce observable effects on BBN, the PBH mass must exceed $10^{9}$ g, a threshold higher than that reported in some earlier studies. Slightly above $10^{9}$ g, the BBN sensitivity rapidly increases with the mass and then decreases, with the turning point occurring at $2\times10^{9}$ g. For PBHs in the mass range $[10^{9},\ 10^{10}]$ g, current measurements of BBN observables set an upper bound on the initial mass fraction parameter $\beta$ ranging from $10^{-17}$ to $10^{-19}$. To facilitate future improvements, we make our code publicly available, enabling straightforward incorporation of updated nuclear reaction rates, particle-physics inputs, and cosmological data.
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https://arxiv.org/abs/2509.05618
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7383c013a975ebd3db4bfd15ad81287e3e32d2c665ff30e21f1da17414d8971a
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2026-01-01T00:00:00-05:00
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Explaining the Origin of TeV Gamma Rays from M87 During High and Low States
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arXiv:2509.21314v2 Announce Type: replace Abstract: The detection of very high-energy gamma-rays from M87 can provide crucial insights into particle acceleration and radiation mechanisms in jets. The recent observations by the Large High Altitude Air Shower Observatory (LHAASO) detector extend the energy range of TeV gamma-ray astronomy, and also the variability study to the TeV energy domain. We have modelled the low state and flare state multi-wavelength spectral energy distributions of M87 within a time-dependent framework. In our model, the low state gamma-ray flux results from the emissions from the sub-parsec and the kilo-parsec scale jets of M87, whereas the flare state gamma-ray flux is mainly produced in the sub-parsec scale jet. We have shown that the spectral and temporal features of the TeV gamma-ray spectrum of M87 are consistent with this two-zone model, where the contribution from the sub-parsec scale jet significantly increases during the flare state.
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https://arxiv.org/abs/2509.21314
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daafad52b5f83761fde541529bf9b36aea18c0b848ac62be1cd6854ad9f051cd
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2026-01-01T00:00:00-05:00
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FITrig: A High-Performance Detection Technique for Efficient Ultra-Long-Period Pulsars
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arXiv:2509.21754v2 Announce Type: replace Abstract: Ultra-long-period (ULP) pulsars, a newly identified class of celestial transients, offer unique insights into astrophysics, though very few have been detected to date. In radio astronomy, most time-domain detection methods cannot find these pulsars, and current image-based detection approaches still face challenges, including low sensitivity, high false positive rate, and low computational efficiency. In this article, we develop Fast Imaging Trigger (FITrig), a GPU-accelerated, statistics-based method for ULP pulsar detection and localisation. FITrig includes two complementary approaches -- an image domain and an image-frequency domain strategy. FITrig offers advantages by increasing sensitivity to faint pulsars, suppressing false positives (from noise, processing artefacts, or steady sources), and improving search efficiency in large-scale wide-field images. Compared to the state-of-the-art source finder SOFIA 2, FITrig increases the detection speed by 4.3 times for large images ($50\mathrm{K} \times 50\mathrm{K}$ pixels) and reduces false positives by up to 858.8 times (at 6$\sigma$ significance) for the image domain branch, while the image-frequency domain branch suppresses false positives even further. FITrig maintains the capability to detect pulsars that are 20 times fainter than surrounding steady features, even under critical Nyquist sampling conditions. In this article, the performance of FITrig is demonstrated using both real-world data (MeerKAT observations of PSR J0901-4046) and simulated datasets based on MeerKAT and SKA Array Assembly (AA) 2 telescope configurations. With its real-time processing capabilities and scalability, FITrig is a promising tool for next-generation telescopes, such as the SKA, with the potential to uncover hidden ULP pulsars.
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https://arxiv.org/abs/2509.21754
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b0c444d68ddaad273df1800c2d5b611980fe82f512ff88969548488c89f872b0
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2026-01-01T00:00:00-05:00
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Closing the Evidence Gap: reddemcee, a Fast Adaptive Parallel Tempering Sampler
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arXiv:2509.24870v2 Announce Type: replace Abstract: Markov Chain Monte Carlo (MCMC) excels at sampling complex posteriors but traditionally lags behind nested sampling in accurate evidence estimation, which is crucial for model comparison in astrophysical problems. We introduce reddemcee, an Adaptive Parallel Tempering Ensemble Sampler, aiming to close this gap by simultaneously presenting next-generation automated temperature-ladder adaptation techniques and robust, low-bias evidence estimators. reddemcee couples an affine-invariant stretch move with five interchangeable ladder-adaptation objectives, Uniform Swap Acceptance Rate, Swap Mean Distance, Gaussian-Area Overlap, Small Gaussian Gap, and Equalised Thermodynamic Length, implemented through a common differential update rule. Three evidence estimators are provided: Curvature-aware Thermodynamic Integration (TI+), Geometric-Bridge Stepping Stones (SS+), and a novel Hybrid algorithm that blends both approaches (H+). Performance and accuracy are benchmarked on n-dimensional Gaussian Shells, Gaussian Egg-box, Rosenbrock Functions, and exoplanet radial-velocity time-series of HD 20794. Across Shells up to 15 dimensions, reddemcee presents roughly 7 times the effective sampling speed of the best dynamic nested sampling configuration. The TI+, SS+ and H+ estimators recover estimates under 3 percent error and supply realistic uncertainties with as few as six temperatures. In the HD 20794 case study, reddemcee reproduces literature model rankings and yields tighter yet consistent planetary parameters compared with dynesty, with evidence errors that track run-to-run dispersion. By unifying fast ladder adaptation with reliable evidence estimators, reddemcee delivers strong throughput and accurate evidence estimates, often matching, and occasionally surpassing, dynamic nested sampling, while preserving the rich posterior information which makes MCMC indispensable for modern Bayesian inference.
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https://arxiv.org/abs/2509.24870
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2cc207177eb6925d6cf670930eb494a692e035b8b775bd575ae09c90a12ac096
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2026-01-01T00:00:00-05:00
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Dynamical Architectures of S-type Transiting Planets in Binaries II: A Dichotomy in Orbital Alignment of Small Planets in Close Binary Systems
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arXiv:2509.25332v2 Announce Type: replace Abstract: Stellar multiplicity plays a crucial role in shaping planet formation and dynamical evolution. We present a survey of 54 TESS Objects of Interest (TOIs) within 300 pc that exhibit significant Hipparcos-Gaia astrometric accelerations. We identified 35 TOIs with stellar companions at projected separations between $0.1^{\prime\prime}$ to $2^{\prime\prime}$ (or $10-200$ AU). We also identified 12 TOIs that could host planetary-mass or brown dwarf companions, including 6 that are newly discovered. Furthermore, we perform three-dimensional orbital characterization for 12 binaries hosting confirmed planets or planet candidates, allowing us to constrain the line-of-sight mutual inclination, $\Delta I_{\mathrm{los}}$, between the planetary and binary orbits. Combining our sample with previous measurements, we apply Bayesian hierarchical analysis to a total of 26 binary systems with S-type transiting planets ($r_p40$ AU while systems with close-in or eccentric stellar companions (periastron distances $<40$ AU) preserve planet-binary alignment.
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https://arxiv.org/abs/2509.25332
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ef145063d8c9ae3e85c8b91126a9129a7871a0bbaac019cc56ef2706a07b9325
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2026-01-01T00:00:00-05:00
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Effects of Coronal Mass Ejection on PSR J1022+1001 and Possible Mode Change of PSR J2145-0750 in the InPTA DR2
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arXiv:2510.26594v2 Announce Type: replace Abstract: The Indian Pulsar Timing Array (InPTA) has recently published its second data release (DR2), comprising the timing analysis of seven years of data on 27 millisecond pulsars (MSPs), observed simultaneously in the 300-500 MHz (band 3) and 1260-1460 MHz (band 5), using the upgraded Giant Metrewave Radio Telescope (uGMRT). The low-frequency data, particularly in band 3, is highly sensitive to propagation effects such as dispersion measure (DM) fluctuations, which can be imprints of some astrophysical phenomena (scientific outliers). Here, we analyze the two outliers of possible astrophysical origin coming from the band 3 DM time series of two pulsars: PSR J1022+1001, with an ecliptic latitude of -0.06 degree, and PSR J2145-0750, one of the brightest MSPs, with multi-component profile morphology. Our study reveals compelling evidence for a coronal mass ejection (CME) event traced in the data of PSR J1022+1001, and reports evidence for a potential mode-changing event in PSR J2145-0750. By contrasting these two cases, we show that DM fluctuations due to CME interacions and intrinsic mode-changing events produce distinct observational signatures, enabling a physically informed classification of scientific outliers in PTA datasets. Extending the analyses presented here to the full sample of InPTA-DR2 pulsars is expected to reveal additional CME events, and possible mode-changing events. Such detections will not only improve our understanding of solar and pulsar magnetospheric plasma interactions but will also enable more accurate modelling of DM variations, leading to improved pulsar timing solutions, which are crucial for high-precision Pulsar Timing Array (PTA) science.
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https://arxiv.org/abs/2510.26594
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e8260377f98deeb5b84e948e284517eb11d111f012b0d82c3271aa93ea5d21d6
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2026-01-01T00:00:00-05:00
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An alternative theory of magnetic flux tubes in strong fields via axion origin photons
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arXiv:2511.04346v2 Announce Type: replace Abstract: In our alternative theory, built around the coincidence of experimental and theoretical data, three "free" parameters -- the magnetic field in the tachocline of the order of ~10^7 G (see Fig.(A.1) and Eq.(A17) in V. D. Rusov et al. (2021)), the axion mass ma ~3.2*10^{-2} eV (see Eq. (11) in V. D. Rusov et al. (2021)), and the asymmetric dark matter (ADM) in the Universe with mADM ~5 GeV ((see V. D. Rusov et al. (2021); A. C. Vincent et al. (2016)) -- give a complete solution to the problem of the theory of magnetic flux tubes in strong fields with 11-year variations of axion-origin photons, which are caused by and anticorrelated to the 11-year variations in density of ADM, gravitationally captured on the Sun.
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https://arxiv.org/abs/2511.04346
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70e2ce14ba386f680cb885135c56ce3014aa8a43babb3e810f8f656db7cf9771
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2026-01-01T00:00:00-05:00
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EMPEROR I. Exoplanet MCMC parallel tempering for RV orbit retrieval
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arXiv:2511.05331v2 Announce Type: replace Abstract: We present EMPEROR, an open-source Python framework designed for efficient exoplanet detection and characterisation with radial velocities (RV). EMPEROR integrates Dynamic Nested Sampling (DNS) and Adaptive Parallel Tempering (APT) Markov Chain Monte Carlo (MCMC), supporting multiple noise models such as Gaussian Processes (GPs) and Moving Averages (MA). The framework enables systematic model comparison using statistical metrics, including Bayesian evidence ($\ln{\mathcal{Z}}$) and Bayesian Information Criterion (BIC), while providing automated, publish-ready visualisations. EMPEROR is evaluated across three distinct systems to assess its capabilities in different detection scenarios. Sampling performance, model selection, and the search for Earth-mass planets are evaluated in data for 51 Pegasi, HD 55693 and Barnard's Star (GJ 699). For 51 Pegasi, APT achieves an effective sampling increase over DNS by a factor 3.76, while retrieving tighter parameter estimates. For HD 55693 the stellar rotation $P_{\text{rot}}=29.72^{+0.01}_{-0.02}$ and magnetic cycle $P_{\text{mag}}=2557.0^{+70.1}_{-36.7}$ are recovered, while demonstrating the sensitivity of $\ln{\mathcal{Z}}$ to prior selection. For Barnard's star, several noise models are compared, and the confirmed planet parameters are successfully retrieved with all of them. The best model shows a period of 3.1536$\pm$0.0003~d, minimum mass of 0.38$\pm$0.03 M$_{\rm{\oplus}}$, and semi-major axis of 0.02315$\pm$0.00039~AU. Purely statistical inference might be insufficient on its own for robust exoplanet detection. Effective methodologies must integrate domain knowledge, heuristic criteria, and multi-faceted model comparisons. The versatility of EMPEROR in handling diverse noise structures, its systematic model selection, and its improved performance make it a valuable tool for RV exoplanetary studies.
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https://arxiv.org/abs/2511.05331
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b576a5f66873bcdb5542925981c80f3d4837e3c9842d1e266062d369d6cc29dd
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2026-01-01T00:00:00-05:00
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Cosmogenic Origin of KM3-230213A: Delayed Gamma-Ray Emission from A Cosmic-Ray Transient
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arXiv:2511.18144v2 Announce Type: replace Abstract: The highest-energy cosmic neutrino detected by the ARCA detector of KM3NeT has reignited the quest to pinpoint the sources of ultrahigh-energy cosmic rays (UHECRs; $E\gtrsim 0.1$ EeV). By uncovering the associated multimessenger signals, we investigate the origin of the 220 PeV $\nu_\mu$ event KM3-230213A from an unknown transient that accelerated cosmic rays to $\sim 10$ EeV. Unlike an astrophysical origin, where the $\nu_\mu$ is produced inside the source, here we consider UHECR protons that escape the source interact with the cosmic background radiation, producing a PeV-EeV cosmogenic neutrino spectrum. The secondary $e^\pm$ and $\gamma$-rays initiate an electromagnetic cascade, resulting in a cosmogenic $\gamma$-ray spectrum. The latter peaks at a delayed time of $\gtrsim 10^4$ years compared to the light travel time from the transient to observer, due to deflection of charged particles in the extragalactic magnetic field (EGMF). Our results shed light on the nature of the UHECR source for the $\nu_\mu$ event and provide crucial insights into the detection of multi-TeV $\gamma$-rays of cosmogenic origin from similar past cosmological transients. Using the $\gamma$-ray sensitivity of currently operating and next-generation imaging atmospheric Cherenkov telescopes, the flux and time-delay distribution can constrain the source distance. We further show that the detection of such a $\gamma$-ray signal above the background depends on the EGMF strength. Together with the non-detection of coincident spatial or temporal photon counterparts at the current epoch, this detection is the first compelling candidate for a sub-EeV cosmogenic neutrino.
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https://arxiv.org/abs/2511.18144
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71d07a1bbcaeb73f0fbd06169e8fcf99b31a267bd87c2d992864db85df469c59
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2026-01-01T00:00:00-05:00
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Constraining the Properties of GRB Accreting Magnetar with $R/I$ Evolutionary Effects Using \emph{Swift}/XRT Data
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arXiv:2511.22149v2 Announce Type: replace Abstract: A newly born millisecond magnetar has been proposed as one possible central engine of some long gamma-ray bursts (LGRBs) with X-ray plateau. In this work, we used a universal correlation between initial spin period ($P_0$) and surface magnetic field ($B_p$) of newborn magnetar based on an LGRB sample in \cite{Lan2025} to explore the propeller properties of accreting magnetars with $R/I$ evolutionary effects. We found that $B_p-P_0$ relation is approximately consistent with $B_p\propto P_{\rm eq}^{7/6}$. Here $P_{\rm eq}$ is equilibrium spin period in magnetic propeller model. The $B_p-P_0$ relation indicates that $P_0$ may not be true initial spin period of newborn magnetar but had reached an equilibrium spin period via fallback accretion in propeller model. The magnetar accretion rate in our LGRBs is in range of $\dot{M}\sim10^{-5}-10^{-2} M_{\odot} \rm s^{-1}$ by incorporating $R/I$ evolutionary effects and using the transition relation between gravitational mass $M_g$ and baryonic mass $M_b$ in different equations of state. Such accretion rates ensure that the accreting magnetars in our sample survive until reaching the equilibrium spin period, and the accretion rate is one order of magnitude lower compared to the statistical results in \cite{Stratta2018} and \cite{Linweili2020}, which used constant $R/I/M_g$ scenario. We suggested that adopting a constant $R/I/M_g$ scenario for modeling propeller regime in accreting magnetar results in a higher mass accretion rate, which may impair our understanding of the physical nature and its surroundings of accreting magnetar, and low-metallicity progenitors can provide enough material to satisfy the accretion requirements of newborn accreting magnetar in LGRBs.
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https://arxiv.org/abs/2511.22149
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e580a8c22e7d4bac4aeb73bcf09b1c446d59e0e93d3a323a275232116cf88658
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2026-01-01T00:00:00-05:00
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Radio Detection of a Local Little Red Dot
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arXiv:2512.03331v2 Announce Type: replace Abstract: Context. One of the most important discoveries by the James Webb Space Telescope (JWST) is the unexpected existence in the Early Universe (z > 4) of very large quantities of "Little Red Dots" (LRDs), compact luminous red galaxies of intriguing physical properties. One of those intriguing properties is the absence of radio detections in high redshift LRDs. Aims. We wish to know if LRDs have radio emission that may be produced by accreting Intermediate/Supermassive Black Holes (IMBHs/SMBHs) or by frequent supernovae (SNe) from a cluster of massive stars. Methods. Assuming LRDs at high redshifts have not been detected at radio wavelengths due to their large distances and/or present limitations of observational capabilities, we analyse here archive Very Large Array radio observations of J1047+0739 and J1025+1402, two analog candidates of LRDs in the Local Universe (LLRDs) at redshifts z = 0.1 - 0.2. Results. The LLRD source J1047+0739 at z = 0.1682 is detected at 6.0 GHz in 2018 with the VLA-A (Very Large Array) as a compact source with radius less than 0.2 arcsec ($<$700 pc at d = 750 Mpc). Its flux density was 117$\pm$8 $\mu$Jy and its in-band spectral index was -0.85$\pm$0.24, which is typical of optically-thin synchrotron emission. It was also detected at 5.0 GHz in 2010 with the VLA-C, showing a flux density of 130$\pm$9 $\mu$Jy. Conclusions. The observed flux densities can be provided by either a radio luminous supernova or an accreting IMBH/SMBH. However, the lack of important variation in flux density over eight years favors the IMBH/SMBH hypothesis. Radio time monitoring of this and other LLRDs could help clarify the mystery of the radio silence of its cosmological counterparts.
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https://arxiv.org/abs/2512.03331
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766bc8dceffbd0e738c50761a5ac70dafb045e26fe3cb035255f3453984010af
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2026-01-01T00:00:00-05:00
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Resolving dust and Ly{\alpha} emission in a lensed galaxy at the epoch of reionization with JWST/CANUCS
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arXiv:2512.13778v2 Announce Type: replace Abstract: Lyman $\alpha$ emission is highly sensitive to dust and neutral hydrogen and is therefore expected to be strongly suppressed in dusty or gas-rich galaxies during the epoch of reionization (EoR). Nevertheless, numerous moderately dusty Ly$\alpha$ emitters (LAEs) are observed at this epoch, suggesting that complex interstellar medium (ISM) geometries and feedback-driven outflows may facilitate Ly$\alpha$ escape. We investigate the dust, gas, and stellar properties of the gravitationally lensed LAE HCM 6A at $z=6.5676$ to characterize its multiphase ISM and the physical conditions regulating Ly$\alpha$ escape. We combine JWST/NIRISS slitless spectroscopy, HST+JWST/NIRCam imaging, and JWST/NIRSpec slit spectra from the CANUCS program. Using a customized BAGPIPES SED-fitting framework with a flexible attenuation law, we derive stellar, nebular, and dust properties on integrated ($\sim$kpc), slit-level ($\sim$0.1 kpc), and pixel-level ($\sim$25 pc) scales, enabled by strong lensing ($\mu \approx 8.3$-$9.1$). A Ly$\alpha$ map from SLEUTH traces the spatial distribution of Ly$\alpha$ emission. We measure an unlensed stellar mass of $\log M_\ast = 8.3$-$8.4$ and an intrinsic UV magnitude of $M_{\rm UV} = -19.8 \pm 0.1$. The older region (S1) is moderately dusty with consistent stellar and nebular attenuation indicators, implying a uniform ISM geometry, while the youngest region (S3) shows strong discrepancies among dust tracers, indicating a feedback-shaped multiphase ISM. Ly$\alpha$ emission arises primarily from S3, where a dust-cleared central clump enables efficient Ly$\alpha$ escape. We find Calzetti-like attenuation curves with a UV bump that strengthens with stellar age and decreasing $A_V$. Our observations provide a uniquely detailed, spatially resolved view of a moderately dusty LAE during the EoR, demonstrating how feedback and multiphase ISM structure govern Ly$\alpha$ escape.
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https://arxiv.org/abs/2512.13778
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964bc828958d0f1f6a2b8dbcbb8872060d9fb3f149fc1889fca20b49a831e492
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2026-01-01T00:00:00-05:00
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NGC 3521 as the Milky Way near twin: spectral energy distribution from UV to radio decameter ranges
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arXiv:2512.14664v2 Announce Type: replace Abstract: Milky Way analogues (MWAs) are usually selected from structural and kinematic properties, but robust SED-based similarity criteria are limited by heterogeneous photometry and incomplete wavelength coverage. We present a homogeneous, aperture-photometry SED of the Milky Way near-twin NGC~3521 from the ultraviolet to the radio decameter range. Fluxes are measured within a fixed elliptical isophotal aperture using GALEX, SDSS, WISE, Spitzer/MIPS, Herschel/PACS+SPIRE, and VLA data, and supplemented by meter/decameter constraints. We report new observations obtained in Jan-Feb 2022 with the Ukrainian T-shape radio telescope and derive, for the first time, an upper limit in the 24--32~MHz band. The UV-to-decameter SED (27 points) is modelled with \textsc{CIGALE}, including a dedicated low-frequency radio prescription (\texttt{radio_extra}) that accounts for emission and absorption effects. Using ZTF and NEOWISE data (2014--2025), we detect genuine nuclear variability; optical trends at $\sim2^{\prime\prime}$ primarily trace the compact nucleus, while NEOWISE variability reflects a mix of nuclear changes and warm-dust emission within the larger aperture. The preferred fit yields $M_\star \simeq 6.0\times10^{10},M_\odot$, ${\rm SFR}\simeq1.65,M_\odot,{\rm yr}^{-1}$, $M_{\rm dust}\simeq1.3\times10^{8},M_\odot$, and an effective dust temperature of $\sim23$~K. The decameter constraint gives $S_{28,{\rm MHz}}<11.22$~Jy, consistent with expectations for a Milky Way-like system placed at 10.7~Mpc. We conclude that an integrated, homogeneous SED, especially below 100~MHz, provides a complementary diagnostic for identifying and validating MWAs and for interpreting how Milky Way properties would appear to an external observer.
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https://arxiv.org/abs/2512.14664
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df8f68f08a82c6fe56be20dbb49a9db002d2750b6e1d450e4011943cad1c54dd
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2026-01-01T00:00:00-05:00
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Photometric and spectroscopic variability of the blue supergiant rho Leo
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arXiv:2512.15345v2 Announce Type: replace Abstract: Context. The post-main-sequence evolution of massive stars remains poorly understood, particularly for blue supergiants. These objects play a crucial role in the dynamical and chemical evolution of galaxies and exhibit pronounced photometric and spectroscopic variability, often quasi-periodic rather than strictly periodic. Aims. We investigate the variability of the evolved B-type star rho Leo to determine its physical properties, identify the underlying mechanisms driving its variability, and constrain its evolutionary stage. Methods. We analyse long-term spectroscopic and photometric datasets obtained from multiple sources, including the TESS and Kepler space missions and observations with the 1.5 m telescope in Estonia. Period analysis is performed using the Generalized Lomb-Scargle periodogram, Lomb-Scargle pre-whitening, and the Weighted Wavelet Z-Transform. Fundamental stellar parameters are derived by fitting synthetic line profiles computed with the FastWind code to the HARPS spectrum, while the stellar rotation inclination is estimated using the ZPEKTR code. Results. The He I 6678.151 A line shows significant radial-velocity and line-profile moment variations. We detect a set of periods and harmonics spanning approximately 0.8 to 35 days. Some periods remain stable over time, whereas others vary between observing seasons. A comparison of spectroscopic and photometric variability, together with phase-curve morphology, allows us to constrain the origin of several signals. In particular, the approximately 11 day period is attributed to stellar rotation, while the approximately 17 day period is linked to radial pulsations. Conclusions. Although the variability is quasi-periodic, most detected periods persist across multiple seasons. The wide range of timescales suggests that rho Leo is likely evolving along a blue loop following the red supergiant phase.
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https://arxiv.org/abs/2512.15345
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57fb7e7cf172d5067128f554b831955f93e5f4857eaa9fa408bc43dc68e3c7d0
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2026-01-01T00:00:00-05:00
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Long-term monitoring of repeating FRB 20220912A with the uGMRT at low radio frequencies
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arXiv:2512.21889v2 Announce Type: replace Abstract: Some repeating FRBs exhibit occasional extreme repetition rates, but very few show a sustained high activity level. One such hyperactive repeater is FRB 20220912A, which was discovered by CHIME/FRB Collaboration on 2022 September 12. Here, we present results from a long-term monitoring campaign of FRB 20220912A using the upgraded Giant Metrewave Radio Telescope (uGMRT) in the frequency range from 300 to 750 MHz. Over the course of nearly two years, we detected a total of 643 bursts in this frequency range. The source exhibited extreme activity for a few months after its discovery and sustained its active phase for over 500 days, with unsystematic modulations in the activity during this phase. The cumulative energy distributions in both bands show a break, consistent with other active repeaters like FRB 20121102A, FRB 202011124A, etc., suggesting common underlying emission mechanisms. Moreover, we show that the energy distribution shape for FRB 20220912A remains broadly same across a large range of frequencies and over time. Overall, the extended high activity, estimated total energy output, persistent power-law tails in the energy distributions, and the lack of detectable short timescale periodicity favor progenitor models invoking young dynamic magnetars, potentially emitting pulses across large rotation phase ranges.
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https://arxiv.org/abs/2512.21889
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255cd025b7b6dba8d6c74dea8514c2e0b5dfb8631de7aad013daed0bf923a6c8
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2026-01-01T00:00:00-05:00
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Rotation and stability of the circumnuclear gas disk in the Galactic Center potential by the ALMA CMZ Exploration Survey (ACES)
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arXiv:2512.22751v2 Announce Type: replace Abstract: We investigated the gravitational potential and mass distribution in the Galactic Center by examining the morphology and kinematics of the circumnuclear gaseous disk revealed by the molecular line data from the ALMA CMZ Exploration Survey (ACES). We obtain an estimate of the shape of the potential {within the central $\sim 20$ pc} to reproduce the observed properties of the circumnuclear gas disk (CND) by simulating the motion of test particles for various axial ratios and show that the potential is approximately spherical. We construct a rotation curve by applying the terminal velocity method to the position-velocity diagrams, and calculate the mass distribution in the Galactic Center. The distribution of mass density is found to be of cusp type, approximated by $\rho_{\rm mass} \sim 1.56\times 10^5(R/1 {\rm pc})^{-1.9}~M_{\odot} {\rm pc}^{-3}$, where $R$ is the distance from the nucleus. We discuss the tidal effect caused by the gravitational potential that produces the rotation curve and show that the gas disk is stable against self-gravitational contraction within a critical radius of $ R_{\rm T}\sim 14 ~(\rho_{\rm gas}/10^5 {\rm H_2~cm^{-3}})^{-1/2}~{\rm pc}$. This suggests suppression of star formation and a top-heavy IMF in the circmunuclear region.
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https://arxiv.org/abs/2512.22751
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0539b43da3d27cfd22479daded7d86bf4e39f9ab9ba37447a1f5fb0c4e03061f
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2026-01-01T00:00:00-05:00
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Baryogenesis via the Chiral Magnetic Effect in a First-Order Electroweak Phase Transition
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arXiv:2409.16091v2 Announce Type: replace-cross Abstract: In this paper, we investigate the generation of the baryon asymmetry of the universe during the first-order electroweak phase transition. We first study the generation of the helical magnetic field in the framework of the standard model effective field theory with a CP-violating operator. We show that, when the chiral magnetic effect is absent, the helical magnetic field and effective chemical potential cannot generate enough baryon asymmetry when vacuum bubbles collide. We further find that the chiral magnetic effect can amplify the lepton asymmetry in the early universe during the phase transition. We present the baryon asymmetry interpretation requirement on certain parameter spaces of the phase transition and the primordial magnetic field.
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https://arxiv.org/abs/2409.16091
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7a0be03edb4e053decb9941d54c99d388d1c94a1f7c69c9872d5b8808b0676c1
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2026-01-01T00:00:00-05:00
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Predictions on observing hot holographic quark star with gravitational waves
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arXiv:2501.17121v2 Announce Type: replace-cross Abstract: We extract the equation of state of hot quark matter from a holographic 2+1 flavor QCD model, which could form the core of a stable compact star. By adding a thin hadron shell, a new type of hybrid star is constructed. With the temperature serving as a parameter, the EoS varies and we obtain stable stars with mass ranging from about 5 to 30 solar masses, and the maximum compactness around 0.2. The I-Love-Q-C relations are further discussed, and compared with the neutron star cases. These compact stars are candidates for black hole mimickers, which could be observed by gravitational waves and distinguished by properties like nonzero tidal Love number and electromagnetic signals.
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https://arxiv.org/abs/2501.17121
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30581ef2cf06f33047f8547116dd5209f02c30845df2e0c49b40b61239b0aea0
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2026-01-01T00:00:00-05:00
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High-Frequency Thermal Graviton Remnant from the End of Inflation
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arXiv:2504.17533v2 Announce Type: replace-cross Abstract: The standard inflationary theory focuses on the freezing of super-horizon fluctuations, which generate a scale-invariant spectrum, while the sub-horizon modes are expected to remain in thermal equilibrium. Building upon recent development of quantum thermodynamics of the de Sitter universe, we investigate the graviton remnant originating from this thermal horizon radiation released at the end of inflation. Unlike the stochastic background from super-horizon fluctuations, this signal represents a snapshot of the thermal dS state, which subsequently decouples and undergoes cosmological redshift. We present a semi-analytical approximation prediction for this relic background, typically peaking in near MHz band, with characteristic energy density of $\log_{10}(\Omega_{\rm G} h^2) \sim \mathcal{O}(-18)$. These signals occupy a High-Frequency band, offering a potential novel probe of the reheating temperature and the thermal history of the early universe.
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https://arxiv.org/abs/2504.17533
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a181cfeaa391816f696f93fcacfb44d474ec2d87b6da7c2bee03b54c72bfcbf3
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2026-01-01T00:00:00-05:00
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Probing Right Handed Neutrino assisted Reheating with Gravitational Waves and Leptogenesis
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arXiv:2507.09728v2 Announce Type: replace-cross Abstract: We investigate a non-instantaneous reheating period in the early Universe, where the inflaton field decays exclusively to right-handed neutrinos (RHNs). The subsequent decay of these RHNs into Standard Model particles not only drives the transition to a radiation-dominated era but also generates the baryon asymmetry of the Universe via leptogenesis. In this typical reheating scenario, gravitational waves (GWs) can be produced during inflaton decay, both through bremsstrahlung and inflaton scattering processes. While GW production via bremsstrahlung dominates near the end of the reheating phase, inflaton scattering leads to a non-negligible GW contribution near the maximum temperature of the Universe. The combined GW spectrum from both decay and scattering processes lies within the sensitivity range of proposed resonant cavity experiments. This framework thus offers a compelling and unified approach to addressing neutrino mass generation, the baryon asymmetry of the Universe via leptogenesis, and probing the dynamics of a non-instantaneous reheating era.
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https://arxiv.org/abs/2507.09728
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992220c9c1b042f387b167598449466b816d40284b1e99bdebf68826e16a4fcb
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2026-01-01T00:00:00-05:00
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Electromagnetic helicity flux density for radiative systems
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arXiv:2507.14966v2 Announce Type: replace-cross Abstract: We show that the helicity flux density is distinguished from magnetic helicity by analysing Hopf solitons. The electromagnetic (EM) helicity flux and the magnetic helicity are Chern-Simons terms at different hypersurfaces. We find the helicity flux density for a point charge moving with an acceleration, extending the Li\'enard-Wiechert angular distribution of radiant power. We also derive the multipole expansion of the helicity flux density, generalizing the Larmor's formula for the radiant power. These formulae have been applied to discuss the helicity flux density in several toy models such as circular and helical motion as well as soft bremsstrahlung. We also comment on the potential applications of the EM helicity flux density to pulsar systems.
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https://arxiv.org/abs/2507.14966
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Academic Papers
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92746060a01c55a775014942009d04d7834156c2f3f3f580444f79a7207a6cfe
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2026-01-01T00:00:00-05:00
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Importance of relativistic pericenter precession in identifying the presence of a third body near eccentric binaries
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arXiv:2508.17348v2 Announce Type: replace-cross Abstract: Many astrophysical processes can produce gravitational wave (GW) sources with significant orbital eccentricity. These binaries emit bursts of gravitational radiation during each pericenter passage. In isolated systems, the intrinsic timing of these bursts is solely determined by the properties of the binary. The presence of a nearby third body perturbs the system and alters the burst timing. Accurately modeling such perturbations therefore offers a novel approach to detecting the presence of a nearby companion. Existing timing models account for Newtonian dynamics and leading-order radiation reaction effects but neglect the higher order post-Newtonian (PN) contributions to the inner binary. In this paper, we present an improved timing model that incorporates conservative PN corrections that lead to the precession of the binary's pericenter. We find that these PN corrections significantly impact the binary's orbital evolution and the timing of the GW burst. In particular, 1PN precession gives rise to distinctive modulation features in the binary's semilatus rectum and eccentricity. These modulations encode valuable information about the presence and properties of the third body, including its mass and distance. Furthermore, unmodeled 1PN effects significantly bias the tertiary's mass and distance. Finally we assess the detectability of GW bursts from such perturbed systems and demonstrate that the inclusion of PN corrections is crucial for accurately capturing the orbital dynamics of hierarchical triples.
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https://arxiv.org/abs/2508.17348
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Academic Papers
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svg
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032862c63591768b438b9d7569f80003d0a9e449cdb45c17c03ecb96806c0580
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2026-01-01T00:00:00-05:00
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Updating GUT-Scale Pole Higgs Inflation After ACT DR6
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arXiv:2510.02083v2 Announce Type: replace-cross Abstract: We consider models of chaotic inflation driven by the real parts of a conjugate pair of Higgs superfields involved in the spontaneous breaking of a grand unification symmetry at a scale assuming its value within MSSM. We combine a superpotential, which is uniquely determined by applying a continuous R symmetry, with two fractional shift-symmetric Kaehler potentials introducing two free parameters (p,N). The inflationary observables provide an excellent match to the recent ACT data for 1.355<=p<=6.7 and 6x10^-5<= N<=0.7. The attainment of inflation allows for subplanckian inflaton values and possibly detectable primordial gravitational waves with (p,N) values of order unity. A solution to the mu problem of MSSM and baryogenesis via non-thermal leptogenesis can be also accommodated by embedding the model into a B-L extension of MSSM.
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https://arxiv.org/abs/2510.02083
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Academic Papers
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svg
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7d748f8c64d454aae2c0a1b51dae4cc6fec75181c9ab48284fb639622af05ab1
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2026-01-01T00:00:00-05:00
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On the maximum compactness of neutron stars
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arXiv:2510.12870v2 Announce Type: replace-cross Abstract: The stellar compactness, that is, the dimensionless ratio between the mass and radius of a compact star, $\mathcal{C} := M/R$, plays a fundamental role in characterising the gravitational and nuclear-physics aspects of neutron stars. Yet, because the compactness depends sensitively on the unknown equation of state (EOS) of nuclear matter, the simple question: ``how compact can a neutron star be?'' remains unanswered. To address this question, we adopt a statistical approach and consider a large number of parameterised EOSs that satisfy all known constraints from nuclear theory, perturbative Quantum Chromodynamics (QCD), and astrophysical observations. Next, we conjecture that, for any given EOS, the maximum compactness is attained by the star with the maximum mass of the sequence of nonrotating configurations. While we can prove this conjecture for a rather large class of solutions, its general proof is still lacking. However, the evidence from all of the EOSs considered strongly indicates that it is true in general. Exploiting the conjecture, we can concentrate on the compactness of the maximum-mass stars and show that an upper limit appears for the maximum compactness and is given by $\mathcal{C}_{\rm max} = 1/3$. Importantly, this upper limit is essentially independent of the stellar mass and a direct consequence of perturbative-QCD constraints.
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https://arxiv.org/abs/2510.12870
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Academic Papers
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svg
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50a61354fea56603f31c0c666a28d6a48d46798c8ae696f88abd2ec0f4ca2a77
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2026-01-01T00:00:00-05:00
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Net Charge Accretion in Magnetized Kerr Black Holes
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arXiv:2511.22356v3 Announce Type: replace-cross Abstract: We investigate the charging process of a rotating Kerr black hole of mass $M$ and angular momentum $J$ immersed in a stationary, axisymmetric, asymptotically uniform magnetic field of strength $B_{0}$. In Wald's classic analysis (Wald 1974), which was based on the assumption of vanishing injection energy, the black hole was predicted to acquire a universal "saturation charge" $Q_{\mathrm{w}}=2B_{0}J$. However, the physical mechanism that sets the saturation charge must ultimately be governed by the competition between the absorption rates of positively and negatively charged particles. Motivated by this observation, we revisit the problem in the framework of a simple accretion model, where two dilute, equivalent fluxes of charged particles of opposite signs are injected from infinity along the magnetic field lines. The problem then reduces to that of individual particle motion in the electromagnetic field of the magnetized Kerr black hole. Using a combination of numerical and analytical tools, we determine the domains of absorption and establish both lower and upper bounds on the corresponding absorption cross sections. At $Q=Q_\mathrm{w}$ these bounds reveal a systematic difference between the two charge signs. In particular, for sufficiently strong magnetic fields, the lower bound on the absorption cross section for the "attracted" charge exceeds the upper bound for the "repelled" one. This charge accretion imbalance (which we find to become extreme at the limit of large $B_{0}$) indicates a persistent net charge accretion at $Q=Q_{\mathrm{w}}$, implying that the actual saturation charge must differ from Wald's charge $Q_{\mathrm{w}}$.
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https://arxiv.org/abs/2511.22356
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Academic Papers
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svg
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8c493347a9ce857a194d9697ca32a81bb8fe2e838455c63eb8392f5716ccb1e9
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2026-01-01T00:00:00-05:00
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RepoMech: A Method to Reduce the Balance-Sheet Impact of Repo Intermediation
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arXiv:2512.23842v1 Announce Type: new Abstract: A repo trade involves the sale of a security coupled with a contract to repurchase at a later time. Following the 2008 financial crisis, accounting standards were updated to require repo intermediaries, who are mostly banks, to increase recorded assets at the time of the first transaction. Concurrently, US bank regulators implemented a supplementary leverage ratio constraint that reduces the volume of assets a bank is allowed record. The interaction of the new accounting rules and bank regulations limits the volume of repo trades that banks can intermediate. To reduce the balance-sheet impact of repo, the SEC has mandated banks to centrally clear all Treasuries trades. This achieves multilateral netting but shifts counterparty risk onto the clearinghouse, which can distort monitoring incentives and raise trading cost through the imposition of fees. We present RepoMech, a method that avoids these pitfalls by multilaterally netting repo trades without altering counterparty risk.
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https://arxiv.org/abs/2512.23842
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Academic Papers
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