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the astrophysical origin of gravitational wave transients is a timely open question in the wake of discoveries by the laser interferometer gravitational-wave observatory (ligo)/virgo. in active galactic nuclei (agns), binaries form and evolve efficiently by interaction with a dense population of stars and the gaseous agn disk. previous studies have shown that stellar-mass black hole (bh) mergers in such environments can explain the merger rate and the number of suspected hierarchical mergers observed by ligo/virgo. the binary eccentricity distribution can provide further information to distinguish between astrophysical models. here we derive the eccentricity distribution of bh mergers in agn disks. we find that eccentricity is mainly due to binary-single (bs) interactions, which lead to most bh mergers in agn disks having a significant eccentricity at 0.01 hz, detectable by the laser interferometer space antenna. if bs interactions occur in isotropic-3d directions, then 8%-30% of the mergers in agn disks will have eccentricities at 10 hz above e10 hz ≳ 0.03, detectable by ligo/virgo/kamioka gravitational wave detector, while 5%-17% of mergers have e10 hz ≥ 0.3. on the other hand, if bs interactions are confined to the agn-disk plane due to torques from the disk, with 1-20 intermediate binary states during each interaction, or if bhs can migrate to ≲ 10-3 pc from the central supermassive bh, then 10%-70% of the mergers will be highly eccentric (e10 hz ≥ 0.3), consistent with the possible high eccentricity in gw190521. | eccentric black hole mergers in active galactic nuclei |
the direct detection of gravitational waves (gws) from merging binary black holes and neutron stars marks the beginning of a new era in gravitational physics, and it brings forth new opportunities to test theories of gravity. to this end, it is crucial to search for anomalous deviations from general relativity in a model-independent way, irrespective of gravity theories, gw sources, and background spacetimes. in this paper, we propose a new universal framework for testing gravity with gws, based on the generalized propagation of a gw in an effective field theory that describes modification of gravity at cosmological scales. then, we perform a parameter estimation study, showing how well the future observation of gws can constrain the model parameters in the generalized models of gw propagation. | generalized framework for testing gravity with gravitational-wave propagation. i. formulation |
double neutron star (dns) merger events are promising candidates of short gamma-ray burst (sgrb) progenitors as well as high-frequency gravitational wave (gw) emitters. on august 17, 2017, such a coinciding event was detected by both the ligo-virgo gravitational wave detector network as gw170817 and gamma-ray monitor on board nasa's fermi space telescope as grb 170817a. here, we show that the fluence and spectral peak energy of this sgrb fall into the lower portion of the distributions of known sgrbs. its peak isotropic luminosity is abnormally low. the estimated event rate density above this luminosity is at least 19 0-160+440 gpc-3 yr-1, which is close to but still below the dns merger event rate density. this event likely originates from a structured jet viewed from a large viewing angle. there are similar faint soft grbs in the fermi archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sgrbs. | a peculiar low-luminosity short gamma-ray burst from a double neutron star merger progenitor |
on august 17, 2017 the ligo interferometers detected the gravitational wave (gw) signal (gw170817) from the coalescence of binary neutron stars. this signal was also simultaneously seen throughout the electromagnetic (em) spectrum from radio waves to gamma rays. we point out that this simultaneous detection of gw and em signals rules out a class of modified gravity theories, termed "dark matter emulators," which dispense with the need for dark matter by making ordinary matter couple to a different metric from that of gw. we discuss other kinds of modified gravity theories which dispense with the need for dark matter and are still viable. this simultaneous observation also provides the first observational test of einstein's weak equivalence principle (wep) between gravitons and photons. we estimate the shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation by abbott et al. [astrophys. j. lett. 848, l13 (2017)], 10.3847/2041-8213/aa920c) to be about 400 days. using this estimate for the shapiro delay and from the time difference of 1.7 seconds between the gw signal and gamma rays, we can constrain violations of the wep using the parametrized post-newtonian parameter γ , and it is given by |γgw-γem|<9.8 ×10-8. | gw170817 falsifies dark matter emulators |
we present a bimetric low-energy effective theory of fractional quantum hall (fqh) states that describes the topological properties and a gapped collective excitation, known as the girvin-macdonald-platzman (gmp) mode. the theory consists of a topological chern-simons action, coupled to a symmetric rank-2 tensor, and an action à la bimetric gravity, describing the gapped dynamics of a spin-2 mode. the theory is formulated in curved ambient space and is spatially covariant, which allows us to restrict the form of the effective action and the values of phenomenological coefficients. using bimetric theory, we calculate the projected static structure factor up to the k6 order in the momentum expansion. to provide further support for the theory, we derive the long-wave limit of the gmp algebra, the dispersion relation of the gmp mode, and the hall viscosity of fqh states. the particle-hole (ph) transformation of the theory takes a very simple form, making the duality between fqh states and their ph conjugates manifest. we also comment on the possible applications to fractional chern insulators, where closely related structures arise. it is shown that the familiar fqh observables acquire a curious geometric interpretation within the bimetric formalism. | bimetric theory of fractional quantum hall states |
the detection of the binary events gw170817 and gw190814 has provided invaluable constraints on the maximum mass of nonrotating configurations of neutron stars, mtov. however, the large differences in the neutron-star masses measured in gw170817 and gw190814 has also lead to significant tension between the predictions for such maximum masses, with gw170817 suggesting that mtov ≲ 2.3 m⊙, and gw190814 requiring mtov ≳ 2.5 m⊙ if the secondary was a (non- or slowly rotating) neutron star at merger. using a genetic algorithm, we sample the multidimensional space of parameters spanned by gravitational-wave and astronomical observations associated with gw170817. consistent with previous estimates, we find that all of the physical quantities are in agreement with the observations if the maximum mass is in the range of ${m}_{\mathrm{tov}}={2.210}_{-0.123}^{+0.116}\,{m}_{\odot }$ within a 2σ confidence level. by contrast, maximum masses with mtov ≳ 2.5 m⊙, not only require efficiencies in the gravitational-wave emission that are well above the numerical-relativity estimates, but they also lead to a significant underproduction of the ejected mass. hence, the tension can be released by assuming that the secondary in gw190814 was a black hole at merger, although it could have been a rotating neutron star before. | gw170817 and gw190814: tension on the maximum mass |
grandma (global rapid advanced network devoted to the multi-messenger addicts) is a network of 25 telescopes of different sizes, including both photometric and spectroscopic facilities. the network aims to coordinate follow-up observations of gravitational-wave (gw) candidate alerts, especially those with large localization uncertainties, to reduce the delay between the initial detection and the optical confirmation. in this paper, we detail grandma's observational performance during advanced ligo/advanced virgo observing run 3 (o3), focusing on the second part of o3; this includes summary statistics pertaining to coverage and possible astrophysical origin of the candidates. to do so, we quantify our observation efficiency in terms of delay between gw candidate trigger time, observations, and the total coverage. using an optimized and robust coordination system, grandma followed-up about 90 per cent of the gw candidate alerts, that is 49 out of 56 candidates. this led to coverage of over 9000 deg2 during o3. the delay between the gw candidate trigger and the first observation was below 1.5 h for 50 per cent of the alerts. we did not detect any electromagnetic counterparts to the gw candidates during o3, likely due to the very large localization areas (on average thousands of degrees squares) and relatively large distance of the candidates (above 200 mpc for 60 per cent of binary neutron star, bns candidates). we derive constraints on potential kilonova properties for two potential bns coalescences (gw190425 and s200213t), assuming that the events' locations were imaged. | grandma observations of advanced ligo's and advanced virgo's third observational campaign |
two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space and time scales of sea surface height (ssh) signals associated with internal gravity waves (igws). frequency-horizontal wavenumber ssh spectral densities are computed over seven regions of the world ocean from two simulations of the hybrid coordinate ocean model (hycom) and three simulations of the massachusetts institute of technology general circulation model (mitgcm). high wavenumber, high-frequency ssh variance follows the predicted igw linear dispersion curves. the realism of high-frequency motions (>0.87 cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest-resolution runs of each model (1/25° hycom and 1/48° mitgcm) with dynamic height variance frequency spectral density computed from nine in situ profiling instruments. these high-frequency motions are of particular interest because of their contributions to the small-scale ssh variability that will be observed on a global scale in the upcoming surface water and ocean topography (swot) satellite altimetry mission. the variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high wavenumbers (length scales smaller than ∼50 km), especially in the higher-resolution simulations. in the highest-resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales. | spectral decomposition of internal gravity wave sea surface height in global models |
we study a single field axion inflation model in the presence of an su(2) gauge field with a small vev. in order to make the analysis as model-independent as possible, we consider an arbitrary potential for the axion that is able to support the slow-roll inflation. the gauge field is coupled to the axion with a chern-simons interaction λ /f{f}_{μ ν}^a{tilde{f}}_a^{μ ν } where λ /f∼ {o}(10)/m_{pl} . it has a negligible effect on the background evolution, ρ ym/m_{pl^2{h}^2}≲ {ɛ}^2 . however, its quantum fluctuations make a significant contribution to the cosmic perturbation. in particular, the gauge field has a spin-2 fluctuation which explicitly breaks the parity between the left- and right-handed polarization states. the chiral tensor modes are linearly coupled to the gravitational waves and lead to a circularly polarized tensor power spectrum comparable to the unpolarized vacuum power spectrum. moreover, the scalar sector is modified by the linear scalar fluctuations of the gauge field. since the spin-0 and spin-2 fluctuations of the su(2) gauge field are independent, the gauge field can, at the same time, generate a detectable chiral gravitational wave signal and have a negligible contribution to the scalar fluctuations, in agreement with the current cmb observations. | axion inflation with an su(2) gauge field: detectable chiral gravity waves |
gravitational waves (gws) were observed for the first time in 2015, one century after einstein predicted their existence. there is now growing interest to extend the detection bandwidth to low frequency. the scientific potential of multi-frequency gw astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. this is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. the prospect of combining observations from the future space-based instrument lisa together with third generation ground based detectors will open the way toward multi-band gw astronomy, but will leave the infrasound (0.1-10 hz) band uncovered. gw detectors based on matter wave interferometry promise to fill such a sensitivity gap. we propose the european laboratory for gravitation and atom-interferometric research (elgar), an underground infrastructure based on the latest progress in atomic physics, to study space-time and gravitation with the primary goal of detecting gws in the infrasound band. elgar will directly inherit from large research facilities now being built in europe for the study of large scale atom interferometry and will drive new pan-european synergies from top research centers developing quantum sensors. elgar will measure gw radiation in the infrasound band with a peak strain sensitivity of $3.3{\times}1{0}^{-22}/\sqrt{\text{hz}}$ at 1.7 hz. the antenna will have an impact on diverse fundamental and applied research fields beyond gw astronomy, including gravitation, general relativity, and geology. | elgar—a european laboratory for gravitation and atom-interferometric research |
primordial black holes might comprise a significant fraction of the dark matter in the universe and be responsible for the gravitational wave signals from black hole mergers observed by the ligo/virgo collaboration. the spatial clustering of primordial black holes might affect their merger rates and have a significant impact on the constraints on their masses and abundances. we provide some analytical treatment of the primordial black hole spatial clustering evolution, compare our results with some of the existing n-body numerical simulations and discuss the implications for the black hole merger rates. if primordial black holes contribute to a small fraction of the dark matter, primordial black hole clustering is not relevant. on the other hand, for a large contribution to the dark matter, we argue that the clustering may increase the late time universe merger rate to a level compatible with the ligo/virgo detection rate. as for the early universe merger rate of black hole binaries formed at primordial epochs, clustering alleviates the ligo/virgo constraints, but does not evade them. | the clustering evolution of primordial black holes |
we study the electroweak phase transition within a 5d warped model including a scalar potential with an exponential behavior, and strong back-reaction over the metric, in the infrared. by means of a novel treatment of the superpotential formalism, we explore parameter regions that were previously inaccessible. we find that for large enough values of the t'hooft parameter (e.g. n ≃ 25) the holographic phase transition occurs, and it can force the higgs to undergo a first order electroweak phase transition, suitable for electroweak baryogenesis. the model exhibits gravitational waves and colliders signatures. it typically predicts a stochastic gravitational wave background observable both at the laser interferometer space antenna and at the einstein telescope. moreover the radion tends to be heavy enough such that it evades current constraints, but may show up in future lhc runs. | cosmological phase transitions in warped space: gravitational waves and collider signatures |
recent discoveries of massive black holes (mbhs) in dwarf galaxies suggest that they may have a more common presence than once thought. systematic searches are revealing more candidates, but this process could be accelerated by predictions from simulations. we perform a study of several high-resolution, cosmological, zoom-in simulations focusing on dwarf galaxies that host massive black holes at z = 0, with the aim of determining when the black holes are most observable. larger dwarf galaxies are more likely to host mbhs than those of lower mass. about 50 per cent of the mbhs in dwarfs are not centrally located, but rather are wandering within a few kpc of the galaxy centre. the accretion luminosities of mbhs in dwarfs are low throughout cosmic time, rendering them extremely difficult to detect. however, the merger history of these mbhs is optimal for gravitational wave detection by lisa. | multimessenger signatures of massive black holes in dwarf galaxies |
rapid binary population synthesis codes are often used to investigate the evolution of compact-object binaries. they typically rely on analytical fits of single-star evolutionary tracks and parameterized models for interactive phases of evolution (e.g., mass transfer on a thermal timescale, determination of dynamical instability, and common envelope) that are crucial to predict the fate of binaries. these processes can be more carefully implemented in stellar structure and evolution codes such as mesa. to assess the impact of such improvements, we compare binary black hole mergers as predicted in models with the rapid binary population synthesis code cosmic to models ran with mesa simulations through mass transfer and common-envelope treatment. we find that results significantly differ in terms of formation paths, the orbital periods and mass ratios of merging binary black holes, and consequently merger rates. while common-envelope evolution is the dominant formation channel in cosmic, stable mass transfer dominates in our mesa models. depending upon the black hole donor mass, and mass-transfer and common-envelope physics, at subsolar metallicity, cosmic overproduces the number of binary black hole mergers by factors of 2-35 with a significant fraction of them having merger times orders of magnitude shorter than the binary black holes formed when using detailed mesa models. therefore we find that some binary black hole merger rate predictions from rapid population syntheses of isolated binaries may be overestimated by factors of ~ 5-500. we conclude that the interpretation of gravitational-wave observations requires the use of detailed treatment of these interactive binary phases. | binary black hole formation with detailed modeling: stable mass transfer leads to lower merger rates |
we investigate the quark deconfinement phase transition in the context of binary neutron star (bns) mergers. we treat hadronic matter using a brueckner-hartree-fock quantum many-body approach and modern two-body and three-body nuclear interactions derived within chiral effective field theory. quark matter is modeled using an extended version of the bag model. we combine these approaches to construct a new finite-temperature composition-dependent equation of state (eos) with a first-order phase transition between hadrons and deconfined quarks. we perform numerical relativity simulations of bns mergers with this new eos and compare results obtained with or without the deconfinment phase transition. we find that deconfined quark production in a neutron star merger results from matter crossing the phase boundary over a wide range of temperatures and densities. the softening of the eos due to the phase transition causes the merger remnants to be more compact and to collapse to a black hole at earlier times. the phase transition is imprinted on the postmerger gravitational wave (gw) signal duration, amplitude, and peak frequency. however, this imprint is only detectable for binaries with sufficiently long-lived remnants. moreover, the phase transition does not result in significant deviations from quasiuniversal relations for the postmerger gw peak frequency. consequently, the postmerger gw peak frequency alone is not sufficient to conclusively exclude or confirm the presence of a phase transition in a bns merger. we also study the impact of the phase transition on dynamical ejecta, remnant accretion disk masses, r -process nucleosynthetic yields and associated electromagnetic counterparts. while there are differences in the electromagnetic counterparts and nucleosynthesis yields between the purely hadronic models and the models with phase transitions, these can be primarily ascribed to the difference in remnant collapse time between the two, so they are degenerate with other effects. an exception is the nonthermal afterglow caused by the interaction of the fastest component of the dynamical ejecta and the interstellar medium, which is systematically boosted in the binaries with phase transition as a consequence of the more violent merger they experience. | signatures of deconfined quark phases in binary neutron star mergers |
searches for gravitational waves crucially depend on exact signal processing of noisy strain data from gravitational wave detectors, which are known to exhibit significant nonstationary and non-gaussian behavior. in this paper, we study two distinct effects in the ligo/virgo data that reduce the sensitivity of searches: first, variations in the noise power spectral density (psd) on timescales of more than a few seconds; and second, loud and abrupt transient "glitches" of terrestrial or instrumental origin. we derive a simple procedure to correct, at first order, the effect of the variation in the psd on the search background. given the knowledge of the existence of localized glitches, in particular segments of data, we also develop a method to insulate statistical inference from these glitches, so as to cleanly excise them without affecting the search background in neighboring seconds. we show the importance of applying these methods on the publicly available ligo data and estimate an increase in the detection volume of at least 15% from the psd-drift correction alone, due to the improved background distribution. | detecting gravitational waves in data with non-stationary and non-gaussian noise |
one of the crucial windows for distinguishing astrophysical black holes from primordial black holes is through the redshift evolution of their respective merger rates. the low redshift population of black holes of astrophysical origin is expected to follow the star formation rate. the corresponding peak in their merger rate peaks at a redshift smaller than that of the star formation rate peak (zp ≈ 2), depending on the time delay between the formation and mergers of black holes. black holes of primordial origin are going to be present before the formation of the stars, and the merger rate of these sources at high redshift is going to be large. we propose a joint estimation of a hybrid merger rate from the stochastic gravitational wave background, which can use the cosmic history of merger rates to distinguish between the two populations of black holes. using the latest bounds on the amplitude of the stochastic gravitational wave background amplitude from the third observation run of ligo/virgo, we obtain weak constraints at $68{{\ \rm per\ cent}}$ c.l. on the primordial black hole merger rate index $2.56_{-1.76}^{+1.64}$ and astrophysical black hole time delay $6.7_{-4.74}^{+4.22}$ gyr. we should be able to distinguish between the different populations of black holes with the forthcoming o5 and a+ detector sensitivities. | can we distinguish astrophysical from primordial black holes via the stochastic gravitational wave background? |
we explicitly construct a double-field inflationary model, which satisfies the latest planck constraints at the cosmic microwave background (cmb) scales and produces the whole dark matter energy density as primordial black holes (pbhs), in the mass range 10-17 m⊙≲mpbh≲10-13 m⊙ . the pbhs can be produced after the end of slow-roll inflation from the bubbles of true vacuum that nucleate during the course of inflation. obtaining pbhs in this mass range enforces the scale of inflation to be extremely low, 10-7≲h ≲10-3 gev , which makes the efforts to observe gravitational waves at the cmb scales futile, although it is high enough to allow for a successful big bang nucleosynthesis. we will show that the shape of the mass distribution of the pbhs is dependent on how inflation ends and the universe settles from the metastable direction to the true one. end of inflation can also be probed by examining the gravitational waves spectrum. in particular, we show that if exit from the rolling metastable direction to the true vacuum of the potential happens through a first-order phase transition after the end of slow-roll inflation, it leaves behind a stochastic gravitational wave background (sgwb), which is potentially observable by the laser interferometer space antenna. examining the mass distribution of pbhs and possible sgwb from the end of inflation, we may be able to gain invaluable information about the end of inflation. | examining the end of inflation with primordial black hole mass distribution and gravitational waves |
the recent detection of gravitational waves (gws) from the neutron star binary inspiral gw170817 has opened a unique avenue to probe matter and fundamental interactions in previously unexplored regimes. extracting information on neutron star matter from the observed gws requires robust and computationally efficient theoretical waveform models. we develop an approximate frequency-domain gw phase model of a main gw signature of matter: dynamic tides associated with the neutron stars' fundamental oscillation modes (f -modes). we focus on nonspinning objects on circular orbits and demonstrate that, despite its mathematical simplicity, the new "f -mode tidal" (fmtidal) model is in good agreement with the effective-one-body dynamical tides model up to gw frequencies of ≳1 khz and gives physical meaning to part of the phenomenology captured in tidal models tuned to numerical relativity. the advantages of the fmtidal model are that it makes explicit the dependence of the gw phasing on the characteristic equation-of-state parameters, i.e., tidal deformabilities and f -mode frequencies; it is computationally efficient; and it can readily be added to any frequency-domain baseline waveform. the fmtidal model is easily amenable to future improvements and provides the means for a first step towards independently measuring additional fundamental properties of neutron star matter beyond the tidal deformability as well as performing novel tests of general relativity from gw observations. | frequency domain model of f -mode dynamic tides in gravitational waveforms from compact binary inspirals |
r-process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. the timescale and peak luminosity of these transients depend on the composition of the ejecta, which determines the local heating rate from nuclear decays and the opacity. kasen et al. and tanaka & hotokezaka pointed out that lanthanides can drastically increase the opacity in these outflows. we use the new general-purpose nuclear reaction network skynet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions ye, initial specific entropies s, and expansion timescales τ. we find that the ejecta is lanthanide-free for ye ≳ 0.22-0.30, depending on s and τ. the heating rate is insensitive to s and τ, but certain, larger values of ye lead to reduced heating rates, due to individual nuclides dominating the heating. we calculate approximate light curves with a simplified gray radiative transport scheme. the light curves peak at about a day (week) in the lanthanide-free (-rich) cases. the heating rate does not change much as the ejecta becomes lanthanide-free with increasing ye, but the light-curve peak becomes about an order of magnitude brighter because it peaks much earlier when the heating rate is larger. we also provide parametric fits for the heating rates between 0.1 and 100 days, and we provide a simple fit in ye, s, and τ to estimate whether or not the ejecta is lanthanide-rich. | r-process lanthanide production and heating rates in kilonovae |
we study the decay of gravitational waves into dark energy fluctuations π, through the processes γ → ππ and γ → γ π, made possible by the spontaneous breaking of lorentz invariance. within the eft of dark energy (or horndeski/beyond horndeski theories) the first process is large for the operator ½ ~ m42(t) δ g00 ( (3)r + δ kμν δ kμν -δ k2 ), so that the recent observations force ~ m4 = 0 (or equivalently 0αh=). this constraint, together with the requirement that gravitational waves travel at the speed of light, rules out all quartic and quintic glpv theories. additionally, we study how the same couplings affect the propagation of gravitons at loop order. the operator proportional to ~ m42 generates a calculable, non-lorentz invariant higher-derivative correction to the graviton propagation. the modification of the dispersion relation provides a bound on ~ m42 comparable to the one of the decay. conversely, operators up to cubic horndeski do not generate sizeable {higher-derivative corrections.} | gravitational wave decay into dark energy |
we study the scrambling properties of ( d + 1)-dimensional hyperbolic black holes. using the eikonal approximation, we calculate out-of-time-order correlators (otocs) for a rindler-ads geometry with ads radius ℓ, which is dual to a d-dimensional conformal field theory (cft) in hyperbolic space with temperature t = 1 /(2 π ℓ). we find agreement between our results for otocs and previously reported cft calculations. for more generic hyperbolic black holes, we compute the butterfly velocity in two different ways, namely: from shock waves and from a pole-skipping analysis, finding perfect agreement between the two methods. the butterfly velocity vb( t) nicely interpolates between the rindler-ads result {v}_b(t=1/2π ℓ)=1/d-1 and the planar result {v}_b(t≫ 1/ℓ)=√{d/2(d-1)} . | scrambling in hyperbolic black holes: shock waves and pole-skipping |
a measurement of the history of cosmic star formation is central to understanding the origin and evolution of galaxies. the measurement is extremely challenging using electromagnetic radiation: significant modeling is required to convert luminosity to mass, and to properly account for dust attenuation, for example. here we show how detections of gravitational waves from inspiraling binary black holes made by proposed third-generation detectors can be used to measure the star formation rate (sfr) of massive stars with high precision up to redshifts of ∼10. depending on the time-delay model, the predicted detection rates ranges from ∼2310 to ∼56,740 per month with the current measurement of local merger rate density. with 30,000 detections, parameters describing the volumetric sfr can be constrained at the few percent level, and the volumetric merger rate can be directly measured to 3% at z ∼ 2. given a parameterized sfr, the characteristic delay time between binary formation and merger can be measured to ∼60%. | measuring the star formation rate with gravitational waves from binary black holes |
rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. the latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. the sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f-modes and r-modes have been updated. several new sections have been added on equilibria in modified theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in lmxbs, rotating strange stars, and on rotating stars in numerical relativity including both hydrodynamic and magnetohydrodynamic studies of these objects. | rotating stars in relativity |
binary black holes are thought to form primarily via two channels: isolated evolution and dynamical formation. the component masses, spins, and eccentricity of a binary black hole system provide clues to its formation history. we focus on eccentricity, which can be a signature of dynamical formation. employing the spin-aligned eccentric waveform model seobnre, we perform bayesian inference to measure the eccentricity of binary black hole merger events in the first gravitational-wave transient catalogue of ligo and virgo. we find that all of these events are consistent with zero eccentricity. we set upper limits on eccentricity ranging from 0.02 to 0.05 with 90 per cent confidence at a reference frequency of 10 hz. these upper limits do not significantly constrain the fraction of ligo-virgo events formed dynamically in globular clusters, because only ∼ 5 per cent are expected to merge with measurable eccentricity. however, with the gravitational-wave transient catalogue set to expand dramatically over the coming months, it may soon be possible to significantly constrain the fraction of mergers taking place in globular clusters using eccentricity measurements. | searching for eccentricity: signatures of dynamical formation in the first gravitational-wave transient catalogue of ligo and virgo |
we present imrphenomtphm, a phenomenological model for the gravitational-wave signals emitted by the coalescence of quasicircular precessing binary black holes systems. the model is based on the "twisting up" approximation, which maps nonprecessing signals to precessing ones in terms of a time-dependent rotation which can be described by three euler angles and which has been utilized in several frequency-domain waveform models that have become standard tools in gravitational-wave data analysis as well as in several time-domain models. our model is constructed in the time domain, applying the twisting up approximation to the nonprecessing multimode model imrphenomthm, which allows several improvements over the frequency-domain models; we do not use the stationary phase approximation, we employ a simple approximation for the precessing euler angles for the ringdown signal, and we implement a new method for computing the euler angles through the evolution of the spin dynamics of the system, which is more accurate and also computationally efficient. | new twists in compact binary waveform modeling: a fast time-domain model for precession |
recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. this paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. we first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. we then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics. | tabletop experiments for quantum gravity: a user’s manual |
the nanograv collaboration has recently reported evidence for the existence of a stochastic gravitational wave background in the 1-100 nhz frequency range. we argue that such a background could have been produced by magnetohydrodynamic (mhd) turbulence at the qcd scale. from the nanograv measurement, one can infer the magnetic field parameters: a comoving field strength close to microgauss and a correlation length close to 10% of the hubble radius at the qcd phase transition epoch. we point out that the turbulent decay of a nonhelical magnetic field with such parameters leads to a magnetic field at the recombination epoch, which would be sufficiently strong to provide a solution to the hubble tension problem, as recently proposed. we also show that the mhd turbulence interpretation of the nanograv signal can be tested via measurements of the relic magnetic field in the voids of the large scale structure, with gamma-ray telescopes like cta. | nanograv signal from magnetohydrodynamic turbulence at the qcd phase transition in the early universe |
we present new numerical relativity results of neutron star (ns) mergers with chirp mass 1.188 m⊙ and mass ratios q = 1.67 and q = 1.8 using finite-temperature equations of state (eos), approximate neutrino transport, and a subgrid model for magnetohydrodynamics-induced turbulent viscosity. the eos are compatible with nuclear and astrophysical constraints and include a new microphysical model derived from ab initio calculations based on the brueckner-hartree-fock approach. we report for the first time evidence for accretion-induced prompt collapse in high-mass-ratio mergers, in which the tidal disruption of the companion and its accretion on to the primary star determine prompt black hole (bh) formation. as a result of the tidal disruption, an accretion disc of neutron-rich and cold matter forms with baryon masses ∼0.15 m⊙, and it is significantly heavier than the remnant discs in equal-masses prompt-collapse mergers. massive dynamical ejecta of the order of ∼0.01 m⊙ also originate from the tidal disruption. they are neutron-rich and expand from the orbital plane with a crescent-like geometry. consequently, bright, red, and temporally extended kilonova emission is predicted from these mergers. our results show that prompt bh mergers can power bright electromagnetic counterparts for high-mass-ratio binaries, and that the binary mass ratio can be, in principle, constrained from multimessenger observations. | accretion-induced prompt black hole formation in asymmetric neutron star mergers, dynamical ejecta, and kilonova signals |
now that detection of gravitational-wave signals from the coalescence of extra-galactic compact binary star mergers has become nearly routine, it is intriguing to consider other potential gravitational-wave signatures. here we examine the prospects for discovery of continuous gravitational waves from fast-spinning neutron stars in our own galaxy and from more exotic sources. potential continuous-wave sources are reviewed, search methodologies and results presented and prospects for imminent discovery discussed. | searches for continuous-wave gravitational radiation |
we present results of an all-sky search for continuous gravitational waves (cws), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the advanced ligo detectors. three different semicoherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 hz and a first frequency derivative from -1 ×10-8 to 2 ×10-9 hz /s . none of these searches has found clear evidence for a cw signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved. | all-sky search for continuous gravitational waves from isolated neutron stars using advanced ligo o2 data |
atom interferometry tests of universality of free fall based on the differential measurement of two different atomic species provide a useful complement to those based on macroscopic masses. however, when striving for the highest possible sensitivities, gravity gradients pose a serious challenge. indeed, the relative initial position and velocity for the two species need to be controlled with extremely high accuracy, which can be rather demanding in practice and whose verification may require rather long integration times. furthermore, in highly sensitive configurations gravity gradients lead to a drastic loss of contrast. these difficulties can be mitigated by employing wave packets with narrower position and momentum widths, but this is ultimately limited by heisenberg's uncertainty principle. we present a promising scheme that overcomes these problems by compensating the effects of the gravity gradients and circumvents the fundamental limitations due to heisenberg's uncertainty principle. furthermore, it relaxes the experimental requirements on initial colocation by several orders of magnitude. | circumventing heisenberg's uncertainty principle in atom interferometry tests of the equivalence principle |
we prove the existence and the linear stability of cantor families of small amplitude time quasi-periodic standing water wave solutions - namely periodic and even in the space variable x - of a bi-dimensional ocean with finite depth under the action of pure gravity. such a result holds for all the values of the depth parameter in a borel set of asymptotically full measure. this is a small divisor problem. the main difficulties are the quasi-linear nature of the gravity water waves equations and the fact that the linear frequencies grow just in a sublinear way at infinity. we overcome these problems by first reducing the linearized operators obtained at each approximate quasi-periodic solution along the nash-moser iteration to constant coefficients up to smoothing operators, using pseudo-differential changes of variables that are quasi-periodic in time. then we apply a kam reducibility scheme which requires very weak melnikov non-resonance conditions (losing derivatives both in time and space), which we are able to verify for most values of the depth parameter using degenerate kam theory arguments. | time quasi-periodic gravity water waves in finite depth |
we revisit the problem of predicting the spin magnitude and direction of the black hole (bh) resulting from the merger of two bhs with arbitrary masses and spins inspiraling in quasi-circular orbits. we do this by analyzing a catalog of 619 recent numerical-relativity simulations collected from the literature and spanning a large variety of initial conditions. by combining information from the post-newtonian approximation, the extreme mass-ratio limit, and perturbative calculations, we improve our previously proposed phenomenological formulae for the final remnant spin. in contrast with alternative suggestions in the literature, and in analogy with our previous expressions, the new formula is a simple algebraic function of the initial system parameters and is not restricted to binaries with spins aligned/anti-aligned with the orbital angular momentum but can be employed for fully generic binaries. the accuracy of the new expression is significantly improved, especially for almost extremal progenitor spins and for small mass ratios, yielding an rms error σ ≈ 0.002 for aligned/anti-aligned binaries and σ ≈ 0.006 for generic binaries. our new formula is suitable for cosmological applications and can be employed robustly in the analysis of the gravitational waveforms from advanced interferometric detectors. | the final spin from binary black holes in quasi-circular orbits |
connections compatible with degenerate metric structures are known to possess peculiar features: on the one hand, the compatibility conditions involve restrictions on the torsion; on the other hand, torsionfree compatible connections are not unique, the arbitrariness being encoded in a tensor field whose type depends on the metric structure. nonrelativistic structures typically fall under this scheme, the paradigmatic example being a contravariant degenerate metric whose kernel is spanned by a one-form. torsionfree compatible (i.e., galilean) connections are characterised by the gift of a two-form (the force field). whenever the two-form is closed, the connection is said newtonian. such a nonrelativistic spacetime is known to admit an ambient description as the orbit space of a gravitational wave with parallel rays. the leaves of the null foliation are endowed with a nonrelativistic structure dual to the newtonian one, dubbed carrollian spacetime. we propose a generalisation of this unifying framework by introducing a new non-lorentzian ambient metric structure of which we study the geometry. we characterise the space of (torsional) connections preserving such a metric structure which is shown to project to (respectively, embed) the most general class of (torsional) galilean (respectively, carrollian) connections. | connections and dynamical trajectories in generalised newton-cartan gravity. ii. an ambient perspective |
while recent detections of gravitational waves from the mergers of binary black holes match well with the predictions of general relativity, they cannot directly confirm the existence of event horizons. exotic compact objects are motivated by quantum models of black holes and can have exotic structure (or a "wall") just outside the (would-be) horizon. exotic compact objects produce ringdown waveforms similar to the general relativistic black holes, but they are followed by delayed "echoes." by solving linearized einstein equations, we can model these echoes and provide analytic templates that can be used to compare to observations. for concreteness, we consider the gw150914 event, detected by the ligo/virgo collaboration, and study the model dependence of its echo properties. we find that echoes are reasonably approximated by complex gaussians, with amplitudes that decay as a power law in time, while their width in time (frequency) grows (shrinks) over subsequent echoes. we also show that trapped modes between a perfectly reflecting wall and angular momentum barrier in the kerr metric can exhibit superradiant instability over long times, as expected. | black hole echology: the observer's manual |
we explore whether the axion which solves the strong cp problem can naturally be much lighter than the canonical qcd axion. the zn symmetry proposed by hook, with n mirror and degenerate worlds coexisting in nature and linked by the axion field, is considered in terms of generic effective axion couplings. we show that the total potential is safely approximated by a single cosine in the large n limit, and we determine the analytical formula for the exponentially suppressed axion mass. the resulting universal enhancement of all axion interactions relative to those of the canonical qcd axion has a strong impact on the prospects of axion-like particle experiments such as alps ii, iaxo and many others: experiments searching for generic axion-like particles have in fact discovery potential to solve the strong cp problem. the finite density axion potential is also analyzed and we show that the zn asymmetric background of high-density stellar environments sets already significant model-independent constraints: 3 ≤ n ≲ 47 for an axion scale fa ≲ 2.4 × 1015 gev, with tantalizing discovery prospects for any value of fa and down to n ∼ 9 with future neutron star and gravitational wave data, down to the ultra-light mass region. in addition, two specific ultraviolet zn completions are developed: a composite axion one and a ksvz-like model with improved peccei-quinn quality. | an even lighter qcd axion |
matter-wave interferometers with large momentum transfers, irrespective of specific implementations, will face a universal dephasing due to relative accelerations between the interferometric mass and the associated apparatus. here we propose a solution that works even without actively tracking the relative accelerations: putting both the interfering mass and its associated apparatus in a freely falling capsule, so that the strongest inertial noise components vanish due to the equivalence principle. in this setting, we investigate two of the most important remaining noise sources: (a) the noninertial jitter of the experimental setup and (b) the gravity-gradient noise. we show that the former can be reduced below desired values by appropriate pressures and temperatures, while the latter can be fully mitigated in a controlled environment. we finally apply the analysis to a recent proposal for testing the quantum nature of gravity [s. bose et al., phys. rev. lett. 119, 240401 (2017), 10.1103/physrevlett.119.240401] through the entanglement of two masses undergoing interferometry. we show that the relevant entanglement witnessing is feasible with achievable levels of relative acceleration noise. | relative acceleration noise mitigation for nanocrystal matter-wave interferometry: applications to entangling masses via quantum gravity |
we discuss a new scenario for the formation of intermediate mass black holes (imbhs) in dense star clusters. in this scenario, imbhs are formed as a result of dynamical interactions of hard binaries containing a stellar-mass black hole (bh), with other stars and binaries. we discuss the necessary conditions to initiate the process of intermediate mass bh formation and the influence of an imbh on the host global globular cluster (gc) properties. we discuss two scenarios for imbh formation. the slow and fast scenarios. they occur later or earlier in the cluster evolution and require smaller or extremely large central densities, respectively. in our simulations, the formation of imbhs is highly stochastic. in general, higher formation probabilities follow from larger cluster concentrations (i.e. central densities). we further discuss possible observational signatures of the presence of imbhs in gcs that follow from our simulations. these include the spatial and kinematic structure of the host cluster, possible radio, x-ray and gravitational wave emissions due to dynamical collisions or mass transfer and the creation of hypervelocity main-sequence escapers during strong dynamical interactions between binaries and an imbh. all simulations discussed in this paper were performed with the mocca (monte carlo cluster simulator) monte carlo code. mocca accurately follows most of the important physical processes that occur during the dynamical evolution of star clusters but, as with other dynamical codes, it approximates the dissipative processes connected with stellar collisions and binary mergers. | mocca code for star cluster simulations - iv. a new scenario for intermediate mass black hole formation in globular clusters |
we report our identification of the optical afterglow and host galaxy of the short-duration gamma-ray burst sgrb 160821b. the spectroscopic redshift of the host is z = 0.162, making it one of the lowest redshift short-duration gamma-ray bursts (sgrbs) identified by swift. our intensive follow-up campaign using a range of ground-based facilities as well as hubble space telescope, xmm-newton, and swift, shows evidence for a late-time excess of optical and near-infrared emission in addition to a complex afterglow. the afterglow light curve at x-ray frequencies reveals a narrow jet, {θ }j∼ {1.9}-0.03+0.10 deg, that is refreshed at >1 day post-burst by a slower outflow with significantly more energy than the initial outflow that produced the main grb. observations of the 5 ghz radio afterglow shows a reverse shock into a mildly magnetized shell. the optical and near-infrared excess is fainter than at2017gfo associated with gw170817, and is well explained by a kilonova with dynamic ejecta mass m dyn = (1.0 ± 0.6) × 10-3 m ⊙ and a secular (post-merger) ejecta mass with m pm = (1.0 ± 0.6) × 10-2 m ⊙, consistent with a binary neutron star merger resulting in a short-lived massive neutron star. this optical and near-infrared data set provides the best-sampled kilonova light curve without a gravitational wave trigger to date. | short grb 160821b: a reverse shock, a refreshed shock, and a well-sampled kilonova |
we report on the construction of a deep convolutional neural network that can reproduce the sensitivity of a matched-filtering search for binary black hole gravitational-wave signals. the standard method for the detection of well-modeled transient gravitational-wave signals is matched filtering. we use only whitened time series of measured gravitational-wave strain as an input, and we train and test on simulated binary black hole signals in synthetic gaussian noise representative of advanced ligo sensitivity. we show that our network can classify signal from noise with a performance that emulates that of match filtering applied to the same data sets when considering the sensitivity defined by receiver-operator characteristics. | matching matched filtering with deep networks for gravitational-wave astronomy |
the zhaoshan long-baseline atom interferometer gravitation antenna (zaiga) is a new type of underground laser-linked interferometer facility, and is currently under construction. it is in the 200-m-on-average underground of a mountain named zhaoshan which is about 80km southeast to wuhan. zaiga will be equipped with long-baseline atom interferometers, high-precision atom clocks, and large-scale gyros. zaiga facility will take an equilateral triangle configuration with two 1-km-apart atom interferometers in each arm, a 300-m vertical tunnel with atom fountain and atom clocks mounted, and a tracking-and-ranging 1-km-arm-length prototype with lattice optical clocks linked by locked lasers. the zaiga facility will be used for experimental research on gravitation and related problems including gravitational wave detection, high-precision test of the equivalence principle of micro-particles, clock-based gravitational red-shift measurement, rotation measurement and gravitomagnetic effect. | zaiga: zhaoshan long-baseline atom interferometer gravitation antenna |
we discuss a possible connection between the recent nanograv results and the primordial black holes (pbhs) for the ligo-virgo events. in particular, we focus on the axionlike curvaton model, which provides a sizable amount of pbhs and gravitational waves (gws) induced by scalar perturbations around the nanograv frequency range. the inevitable non-gaussianity of this model suppresses the induced gws associated with pbhs for the ligo-virgo events to be compatible with the nanograv results. we show that the axionlike curvaton model can account for pbhs for the ligo-virgo events and the nanograv results simultaneously. | nanograv results and ligo-virgo primordial black holes in axionlike curvaton models |
the first detection of gravitational waves from a neutron star-neutron star merger, gw170817, has opened up a new avenue for constraining the ultradense-matter equation of state (eos). the deviation of the observed waveform from a point-particle waveform is a sensitive probe of the eos controlling the merging neutron stars' structure. in this topical review, i discuss the various constraints that have been made on the eos in the year following the discovery of gw170817. in particular, i review the surprising relationship that has emerged between the effective tidal deformability of the binary system and the neutron star radius. i also report new results that make use of this relationship, finding that the radius inferred from gw170817 lies between 9.8 and 13.2km at 90% confidence, with distinct likelihood peaks at 10.8 and 12.3km. i compare these radii, as well as those inferred in the literature, to x-ray measurements of the neutron star radius. i also summarize the various maximum mass constraints, which point towards a maximum mass ≲2 .3 m⊙ , depending on the fate of the remnant, and which can be used to additionally constrain the high-density eos. i review the constraints on the eos that have been performed directly, through bayesian inference schemes. finally, i comment on the importance of disentangling thermal effects in future eos constraints from neutron star mergers. | constraints on the neutron star equation of state from gw170817 |
we investigate the sensitivity of future space-based interferometers such as lisa and decigo to the parameters of new particle physics models which drive a first-order phase transition in the early universe. we first perform a fisher matrix analysis on the quantities characterizing the gravitational-wave spectrum resulting from the phase transition, such as the peak frequency and amplitude. we next perform a fisher analysis for the quantities which determine the properties of the phase transition, such as the latent heat and the time dependence of the bubble nucleation rate. since these quantities are determined by the model parameters of the new physics, we can estimate the expected sensitivities to such parameters. we illustrate this point by taking three new physics models for example: (i) models with additional isospin singlet scalars, (ii) a model with an extra real higgs singlet, and (iii) a classically conformal b -l model. we find that future gravitational-wave observations play complementary roles to future collider experiments in pinning down the parameters of new physics models driving a first-order phase transition. | selecting models of first-order phase transitions using the synergy between collider and gravitational-wave experiments |
we present a rapid analytic framework for predicting kilonova light curves following neutron star (ns) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum ns mass). this enables synthesis of a kilonova sample for any ns source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. we validate this code, implemented in the public mosfit package, by fitting it to gw170817. a bayes factor analysis overwhelmingly (b > 1010) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. this is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. the emission thereafter is dominated by a lanthanide-rich viscous wind. we find the mass ratio of the binary is q = 0.92 ± 0.07 (90 per cent credible interval). we place tight constraints on the maximum stable ns mass, mtov $=2.17^{+0.08}_{-0.11}$ m⊙. for a uniform prior in tidal deformability, the radius of a 1.4-m⊙ ns is r1.4 ~ 10.7 km. re-weighting with a prior based on equations of state that support our credible range in mtov, we derive a final measurement r1.4 $=11.06^{+1.01}_{-0.98}$ km. applying our code to the second gravitationally detected ns merger, gw190425, we estimate that an associated kilonova would have been fainter (by ~0.7 mag at 1 d post-merger) and declined faster than gw170817, underlining the importance of tuning follow-up strategies individually for each gw-detected ns merger. | tight multimessenger constraints on the neutron star equation of state from gw170817 and a forward model for kilonova light-curve synthesis |
strong lensing by intervening galaxies can produce multiple images of gravitational waves from sources at cosmological distances. these images acquire additional phase-shifts as the over-focused wavefront passes through itself along the line of sight. time domain waveforms of type-ii images (associated with saddle points of the time delay) exhibit a non-trivial distortion from the unlensed waveforms. this phenomenon is in addition to the usual frequency-independent magnification, and happens even in the geometric limit where the wavelength is much shorter than the deflector's gravitational length scale. similarly, type-iii images preserve the original waveform's shape but exhibit a sign flip. we show that for non-precessing binaries undergoing circular inspiral and merger, these distortions are equivalent to rotating the line of sight about the normal to the orbital plane by $45^\circ$ (type ii) and $90^\circ$ (type iii). this effect will enable us to distinguish between the different topological types among a set of multiple images, and give us valuable insight into the lens model. furthermore, we show that for eccentric binaries, the waveform of a type-ii image is distorted in a manner that is inequivalent to a change of the source's orbital parameters. | on the waveforms of gravitationally lensed gravitational waves |
we present a new effective-one-body (eob) model for eccentric binary coalescences. the model stems from the state-of-the-art model teobiresums_sm for circularized coalescing black-hole binaries, that is modified to explicitly incorporate eccentricity effects both in the radiation reaction and in the waveform. using regge-wheeler-zerilli-type calculations of the gravitational wave losses as benchmarks, we find that a rather accurate (∼1 %) expression for the radiation reaction along mildly eccentric orbits (e ∼0.3 ) is given by dressing the current, eob-resummed, circularized angular momentum flux, with a leading-order (newtonian-like) prefactor valid along general orbits. an analogous approach is implemented for the waveform multipoles. the model is then completed by the usual merger-ringdown part informed by circularized numerical relativity (nr) simulations. the model is validated against the 22, publicly available, nr simulations calculated by the simulating extreme spacetime (sxs) collaboration, with mild eccentricities, mass ratios between 1 and 3, and up to rather large dimensionless spin values (±0.7 ). the maximum eob/nr unfaithfulness, calculated with advanced ligo noise, is at most of order 3%. the analytical framework presented here should be seen as a promising starting point for developing highly faithful waveform templates driven by eccentric dynamics for present, and possibly future, gravitational wave detectors. | faithful analytical effective-one-body waveform model for spin-aligned, moderately eccentric, coalescing black hole binaries |
we present new 0.6-10 ghz observations of the binary neutron star merger gw170817 covering the period up to 300 days post-merger, taken with the upgraded karl g. jansky very large array, the australia telescope compact array, the giant metrewave radio telescope and the meerkat telescope. we use these data to precisely characterize the decay phase of the late-time radio light curve. we find that the temporal decay is consistent with a power-law slope of t -2.2, and that the transition between the power-law rise and decay is relatively sharp. such a slope cannot be produced by a quasi-isotropic (cocoon-dominated) outflow, but is instead the classic signature of a relativistic jet. this provides strong observational evidence that gw170817 produced a successful jet, and directly demonstrates the link between binary neutron star mergers and short-hard gamma-ray bursts. using simple analytical arguments, we derive constraints on the geometry and the jet opening angle of gw170817. these results are consistent with those from our companion very long baseline interferometry paper, reporting superluminal motion in gw170817. | a strong jet signature in the late-time light curve of gw170817 |
we estimate the potential of present and future interferometric gravitational-wave detectors to test the kerr nature of black holes through "gravitational spectroscopy," i.e., the measurement of multiple quasinormal mode frequencies from the remnant of a black hole merger. using population synthesis models of the formation and evolution of stellar-mass black hole binaries, we find that voyager-class interferometers will be necessary to perform these tests. gravitational spectroscopy in the local universe may become routine with the einstein telescope, but a 40-km facility like cosmic explorer is necessary to go beyond z ∼3 . in contrast, detectors like elisa (evolved laser interferometer space antenna) should carry out a few—or even hundreds—of these tests every year, depending on uncertainties in massive black hole formation models. many space-based spectroscopical measurements will occur at high redshift, testing the strong gravity dynamics of kerr black holes in domains where cosmological corrections to general relativity (if they occur in nature) must be significant. | spectroscopy of kerr black holes with earth- and space-based interferometers |
very recently a compact object with a mass in the range 2.50 ÷ 2.67m⊙ has been discovered via gravitational waves detection of a compact binary coalescence. the mass of this object makes it among the heaviest neutron star never detected or the lightest black hole ever observed. here we show that a neutron star with this observed mass, can be consistently explained with the mass-radius relation obtained by extended theories of gravity. furthermore, equations of state, consistent with ligo observational constraints, are adopted. we consider also the influence of rotation and show that masses of rotating neutron stars can exceed 2.6m⊙ for some equations of state compatible with ligo data. | extended gravity description for the gw190814 supermassive neutron star |
spherically symmetric bosonic stars are one of the few examples of gravitating solitons that are known to form dynamically, via a classical process of (incomplete) gravitational collapse. as stationary solutions of the einstein-klein-gordon or the einstein-proca theory, bosonic stars may also become sufficiently compact to develop light rings and hence mimic, in principle, gravitational-wave observational signatures of black holes (bhs). in this paper, we discuss how these horizonless ultracompact objects (ucos) are actually distinct from bhs, both phenomenologically and dynamically. in the electromagnetic channel, the light ring associated phenomenology reveals remarkable lensing patterns, quite distinct from a standard bh shadow, with an infinite number of einstein rings accumulating in the vicinity of the light ring, both inside and outside the latter. the strong lensing region, moreover, can be considerably smaller than the shadow of a bh with a comparable mass. dynamically, we investigate the fate of such ucos under perturbations, via fully nonlinear numerical simulations and observe that, in all cases, they decay into a schwarzschild bh within a time scale of o (m ), where m is the mass of the bosonic star. both these studies reinforce how difficult it is for horizonless ucos to mimic bh phenomenology and dynamics, in all its aspects. | lensing and dynamics of ultracompact bosonic stars |
the dynamical generation of right-handed-neutrino (rhn) masses in the early universe naturally entails the formation of cosmic strings that give rise to an observable signal in gravitational waves (gws). in this paper, we show that a characteristic break in the gw spectrum would provide evidence for a nonstandard stage in the cosmological expansion history and a suppression of the rhn mass scale compared to the scale of spontaneous symmetry breaking. the detection of such a spectral feature would thus represent a unique possibility to probe the physics of rhn mass generation in regions of parameter space that allow for low-scale leptogenesis in accord with electroweak naturalness. | fingerprint of low-scale leptogenesis in the primordial gravitational-wave spectrum |
black hole (bh) high mass x-ray binary (hmxb) systems are likely the progenitors of the bh-bh mergers detected in gravitational waves by ligo/virgo/kagra (lvk). yet bhs in the gravitational wave sources reach higher masses (100msun) than bhs in hmxbs (20msun), and have typically lower spins (a<0.25 with tail extending to larger values) than the published values for bhs in hmxbs (a>0.9). this could suggest that these two classes of systems belong to different populations (apples and oranges) but we show here that it does not have to be the case. the difference in masses is easily explained as the known hmxb-bhs are in galaxies with relatively high-metallicity, so their progenitor stars are subject to strong mass loss from winds which leads to relatively low mass bh at core collapse. conversely, lvk allows for detection of bhs from low-metallicity galaxies that naturally produce more massive stellar-origin bhs. the explanation of the difference in bh spins is not as straightforward, but we show that in hmxbs the bh spin value derivation depends strongly on how the hmxb accretion disk emission is modeled. we demonstrate this explicitly for the case of cyg x-1, showing excellent spectral fits with low spin (a=0.1) when taking into account the comptonization of the disk photosphere. similar results have recently been shown for lmc x-1 (allowing for a=0.1). we suggest that such low bh spins are generic for all three hmxb bhs. hence we conclude that current observations are consistent with lvk bhs and hmxb bhs belonging to the same population (all apples). | common origin of black holes in high mass x-ray binaries and in gravitation-wave sources |
the classical double copy procedure relates classical asymptotically-flat gravitational field solutions to yang-mills and scalar field solutions living in minkowski space. in this paper we extend this correspondence to maximally symmetric curved spacetimes. we consider asymptotically (a)ds spacetimes in kerr-schild form and construct the corresponding single and zeroth copies. in order to clarify the interpretation of these copies, we study several examples including (a)ds-schwarzschild, (a)ds-kerr, black strings, black branes, and waves, paying particular attention to the source terms. we find that the single and zeroth copies of stationary solutions satisfy different equations than those of wave solutions. we also consider how to obtain einstein-maxwell solutions using this procedure. finally, we derive the classical single and zeroth copy of the btz black hole. | the classical double copy in maximally symmetric spacetimes |
we study the effect of nonquadrupolar modes in the detection and parameter estimation of gravitational waves (gws) from black hole binaries with nonprecessing spins, using advanced ligo. we evaluate the loss of the signal-to-noise ratio (snr) and the systematic errors in the estimated parameters when a quadrupole-mode template family is used to detect gw signals with all the relevant modes. target signals including nonquadrupole modes are constructed by matching numerical-relativity simulations of nonprecessing black hole binaries describing the late inspiral, merger, and ringdown with post-newtonian/effective-one-body waveforms describing the early inspiral. we find that neglecting nonquadrupole modes will, in general, cause unacceptable loss in the detection rate and unacceptably large systematic errors in the estimated parameters, for the case of massive binaries with large mass ratios. for a given mass ratio, neglecting subdominant modes will result in a larger loss in the detection rate for binaries with aligned spins. for binaries with antialigned spins, quadrupole-mode templates are more effectual in detection, at the cost of introducing a larger systematic bias in the parameter estimation. we provide a summary of the regions in the parameter space where neglecting nonquadrupole modes will cause an unacceptable loss of detection rates and unacceptably large systematic biases in the estimated parameters. | effects of nonquadrupole modes in the detection and parameter estimation of black hole binaries with nonprecessing spins |
gravitational waves can be focussed by the gravity of an intervening galaxy, just like light, thereby magnifying binary merging events in the far universe. high magnification by galaxies is found to be responsible for the brightest sources detected in sky surveys, but the low angular resolution of ligo/virgo is insufficient to check this lensing possibility directly. here we find that the first six binary black hole (bbh) merging events reported by ligo/virgo show clear evidence for lensing in the plane of observed mass and source distance. the four lowest frequency events follow an apparent locus in this plane, which we can reproduce by galaxy lensing, where the higher the magnification, the generally more distant the source so the wave train is stretched more by the universal expansion, by factors of 2-4. this revises the reported bbh distances upwards by an order of magnitude, equal to the square root of the magnification. furthermore, the reported black hole masses must be decreased by 2-4 to counter the larger stretch factor, since the orbital frequency is used to derive the black hole masses. this lowers the masses to 5-15 solar masses, well below the puzzlingly high values of 20-35 solar masses otherwise estimated, with the attraction of finding agreement in mass with black holes orbiting stars in our own galaxy, thereby implying a stellar origin for the low frequency events in the far universe. we also show that the other two bbh events of higher frequency detected by ligo/virgo, lie well below the lensing locus, consistent with being nearby and unlensed. if this apparent division between local and distant lensed events is reinforced by new detections then the spins and masses of stellar black holes can be compared over a timespan of 10 billion years by ligo/virgo. | reinterpreting low frequency ligo/virgo events as magnified stellar-mass black holes at cosmological distances |
upcoming observational runs of the ligo-virgo-kagra collaboration and future gravitational-wave (gw) detectors on the ground and in space require waveform models more accurate than currently available. high-precision waveform models can be developed by improving the analytical description of compact binary dynamics and completing it with numerical-relativity (nr) information. here, we assess the accuracy of the recent results for the fourth post-minkowskian (4pm) conservative dynamics through comparisons with nr simulations for the circular-orbit binding energy and for the scattering angle. we obtain that the 4pm dynamics gives better agreement with nr than the 3pm dynamics and that while the 4pm approximation gives comparable results to the third post-newtonian (pn) approximation for bound orbits it performs better for scattering encounters. furthermore, we incorporate the 4pm results in effective-one-body (eob) hamiltonians, which improves the disagreement with nr over the 4pm-expanded hamiltonian from ∼40 % to ∼10 %, or ∼3 % depending on the eob gauge, for an equal-mass binary, two gw cycles before merger. finally, we derive a 4pn-eob hamiltonian for hyperbolic orbits and compare its predictions for the scattering angle to nr and to the scattering angle of a 4pn-eob hamiltonian computed for elliptic orbits. | energetics and scattering of gravitational two-body systems at fourth post-minkowskian order |
the growing number of stellar-mass binary black hole mergers discovered by advanced ligo and advanced virgo are starting to constrain the binaries’ origin and environment. however, we still lack sufficiently accurate modeling of binary formation channels to obtain strong constraints, or to identify subpopulations. one promising formation mechanism that could result in different black hole properties is binaries merging within the accretion disks of active galactic nuclei (agns). here we show that the black holes’ orbital alignment with the agn disks preferentially selects heavier black holes. we carry out monte carlo simulations of orbital alignment with agn disks, and find that agns harden the initial black hole mass function. assuming an initial power-law mass distribution {m}bh}-β , we find that the power-law index changes by δβ ∼ 1.3, resulting in a more top-heavy population of merging black holes. this change is independent of the mass of, and accretion rate onto, the supermassive black hole in the center of the agn. our simulations predict an agn-assisted merger rate of ∼4 gpc-3 yr-1. with its hardened mass spectra, the agn channel could be responsible for 10%-50% of gravitational-wave detections. | agn disks harden the mass distribution of stellar-mass binary black hole mergers |
in this paper we calculate the scalar induced gravitational waves (sigws) accompanying the formation of primordial black holes during the radiation dominated era in three different gauges, i.e., the synchronous gauge, newton gauge, and uniform curvature gauge, and we find that the energy density spectra of sigws, ωgw(k ), are identical in these three different gauges. | scalar induced gravitational waves in different gauges |
we perform a joint bayesian inference of neutron-star mass and radius constraints based on gw170817, observations of quiescent low-mass x-ray binaries (qlmxbs), photospheric radius expansion x-ray bursting sources, and x-ray timing observations of j 0030 +0451 . with this dataset, the form of the prior distribution still has an impact on the posterior mass-radius curves and equation of state (eos), but this impact is smaller than recently obtained when considering qlmxbs alone. we analyze the consistency of the electromagnetic data by including an "intrinsic scattering" contribution to the uncertainties, and find only a slight broadening of the posteriors. this suggests that the gravitational-wave and electromagnetic observations of neutron-star structure are providing a consistent picture of the neutron-star mass-radius curve and the eos. | combining electromagnetic and gravitational-wave constraints on neutron-star masses and radii |
we present realistic expectations for the number and properties of neutron star binary mergers to be detected as multi-messenger sources during the upcoming fourth observing run (o4) of the ligo-virgo-kagra gravitational-wave (gw) detectors, with the aim of providing guidance for the optimization of observing strategies. our predictions are based on a population synthesis mode, which includes the gw signal-to-noise ratio, the kilonova (kn) optical and near-infrared light curves, the relativistic jet gamma-ray burst (grb) prompt emission peak photon flux, and the afterglow light curves in radio, optical, and x-rays. within our assumptions, the rate of gw events to be confidently detected during o4 is ${7.7}_{-5.7}^{+11.9}$ yr-1 (calendar year), 78% of which will produce a kn, and a lower 52% will also produce a relativistic jet. the typical depth of current optical electromagnetic search and follow-up strategies is still sufficient to detect most of the knæ in o4, but only for the first night or two. the prospects for detecting relativistic jet emission are not promising. while closer events (within z ≲ 0.02) will likely still have a detectable cocoon shock breakout, most events will have their grb emission (both prompt and afterglow) missed unless seen under a small viewing angle. this reduces the fraction of events with detectable jets to 2% (prompt emission, serendipitous) and 10% (afterglow, deep radio monitoring), corresponding to detection rates of ${0.17}_{-0.13}^{+0.26}$ and ${0.78}_{-0.58}^{+1.21}$ yr-1, respectively. when considering a gw subthreshold search triggered by a grb detection, our predicted rate of joint gw+grb prompt emission detections increases up to a more promising ${0.75}_{-0.55}^{+1.16}$ yr-1. | multi-messenger observations of binary neutron star mergers in the o4 run |
matrix theory is a proposed non-perturbative definition of superstring theory in which space is emergent. we begin a study of cosmology in the context of matrix theory. specifically, we show that matrix theory can lead to an emergent non-singular cosmology which, at late times, can be described by an expanding phase of standard big bang cosmology. the horizon problem of standard big bang cosmology is automatically solved. we show that thermal fluctuations in the emergent phase source an approximately scale-invariant spectrum of cosmological perturbations and a scale-invariant spectrum of gravitational waves. hence, it appears that matrix theory can lead to a successful scenario for the origin of perturbations responsible for the currently observed structure in the universe while providing a consistent uv-complete description. | emergent cosmology from matrix theory |
multi-messenger gravitational wave (gw) observation for binary neutron star merger events could provide a rather useful tool to explore the evolution of the universe. in particular, for the third-generation gw detectors, i.e. the einstein telescope (et) and the cosmic explorer (ce), proposed to be built in europe and the u.s., respectively, lots of gw standard sirens with known redshifts could be obtained, which would exert great impacts on the cosmological parameter estimation. the total neutrino mass could be measured by cosmological observations, but such a measurement is model-dependent and currently only gives an upper limit. in this work, we wish to investigate whether the gw standard sirens observed by et and ce could help improve the constraint on the neutrino mass, in particular in the interacting dark energy (ide) models. we find that the gw standard siren observations from et and ce can only slightly improve the constraint on the neutrino mass in the ide models, compared to the current limit. the improvements in the ide models are weaker than those in the standard cosmological model. although the limit on neutrino mass can only be slightly updated, the constraints on other cosmological parameters can be significantly improved by using the gw observations. | impacts of gravitational-wave standard siren observations from einstein telescope and cosmic explorer on weighing neutrinos in interacting dark energy models |
the tropopause layer plays a key role in manifold processes in atmospheric chemistry and physics. here we compare the representation and characteristics of the lapse rate tropopause according to the definition of the world meteorological organization (wmo) as estimated from european centre for medium-range weather forecasts (ecmwf) reanalysis data. our study is based on 10-year records (2009 to 2018) of ecmwf's state-of-the-art reanalysis era5 and its predecessor era-interim. the intercomparison reveals notable differences between era5 and era-interim tropopause data, in particular on small spatiotemporal scales. the monthly mean differences of era5 minus era-interim tropopause heights vary between −300 m at the transition from the tropics to the extratropics (near 30∘ s and 30∘ n) to 150 m around the equator. mean tropopause temperatures are mostly lower in era5 than in era-interim, with a maximum difference of up to −1.5 k in the tropics. monthly standard deviations of tropopause heights of era5 are up to 350 m or 60 % larger than for era-interim. monthly standard deviations of tropopause temperatures of era5 exceed those of era-interim by up to 1.5 k or 30 %. the occurrence frequencies of double-tropopause events in era5 exceed those of era-interim by up to 25 percentage points at middle latitudes. we attribute the differences between the era5 and era-interim tropopause data and the larger, more realistic variability of era5 to improved spatiotemporal resolution and better representation of geophysical processes in the forecast model as well as improvements in the data assimilation scheme and the utilization of additional observations in era5. the improved spatiotemporal resolution of era5 allows for a better representation of mesoscale features, in particular of gravity waves, which affect the temperature profiles in the upper troposphere and lower stratosphere (utls) and thus the tropopause height estimates. we evaluated the quality of the era5 and era-interim reanalysis tropopause data by comparisons with cosmic and metop global positioning system (gps) satellite observations as well as high-resolution radiosonde profiles. the comparison indicates an uncertainty of the first tropopause for era5 (era-interim) of about ±150 to ±200 m (±250 m) based on radiosonde data and ±120 to ±150 m (±170 to ±200 m) based on the coarser-resolution gps data at different latitudes. consequently, era5 will provide more accurate information than era-interim for future tropopause-related studies. | an assessment of tropopause characteristics of the era5 and era-interim meteorological reanalyses |
hierarchical triple-star systems are expected to form frequently via close binary-binary encounters in the dense cores of globular clusters (gcs). in a sufficiently inclined triple, gravitational interactions between the inner and outer binary can cause large-amplitude oscillations in the eccentricity of the inner orbit (“lidov-kozai (lk) cycles”), which can lead to a collision and merger of the two inner components. in this paper we use monte carlo models of dense star clusters to identify all triple systems formed dynamically and we compute their evolution using a highly accurate three-body integrator which incorporates relativistic and tidal effects. we find that a large fraction of these triples evolve through a non-secular dynamical phase which can drive the inner binary to higher eccentricities than predicted by the standard secular perturbation theory (even including octupole-order terms). we place constraints on the importance of lk-induced mergers for producing: (i) gravitational wave sources detectable by advanced ligo (aligo), for triples with an inner pair of stellar black holes (bhs); and (ii) blue straggler stars, for triples with main-sequence-star components. we find a realistic aligo detection rate of bh mergers due to the lk mechanism of ∼1 yr-1, with about 20% of these having a finite eccentricity when they first chirp into the aligo frequency band. while rare, these events are likely to dominate among eccentric compact object inspirals that are potentially detectable by aligo. for blue stragglers, we find that the lk mechanism can contribute up to ∼10% of their total numbers in gcs. | black hole mergers and blue stragglers from hierarchical triples formed in globular clusters |
astrophysical black holes are generally surrounded by accretion disks, galactic matter and the omnipresent cosmic microwave background radiation, thus allowing for the concurrent propagation of both gravitational and sound waves. recently, acoustic black holes were embedded in schwarzschild spacetime allowing for the coexistence of event and acoustic horizons. here, we obtain a class of perturbative solutions to the field equations of the relativistic gross-pitaevskii and yang-mills theories, which describe sound waves propagating on a curved slowly-rotating acoustic black hole, akin to lense-thirring spacetime. we investigate the quasinormal mode frequencies, hawking-unruh radiation, and quasibound states. our novel metric mimics the gravitational field of astrophysical compact objects in the limiting case of slow rotation, and therefore could, in principle, shed more light into the underlying classical and quantum physics of black holes through analog acoustic probes. | slowly-rotating curved acoustic black holes: quasinormal modes, hawking-unruh radiation, and quasibound states |
cosmological α-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (cmb) experiments. we investigate α-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. we study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space. in the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non-geodesic motion in field space. the two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. these enhanced scalar perturbations can lead to primordial black hole (pbh) production and second-order gravitational wave (gw) generation. due to the existence of universal predictions in α-attractors, consistency with current cmb constraints on the large-scale spectral tilt implies that pbhs can only be produced with masses smaller than 108 g and are accompanied by ultra-high frequency gws, with a peak expected to be at frequencies of order 10 khz or above. | revisiting small-scale fluctuations in α-attractor models of inflation |
we study the energy budget of a first-order cosmological phase transition, which is an important factor in the prediction of the resulting gravitational wave spectrum. formerly, this analysis was based mostly on simplified models as for example the bag equation of state. here, we present a model-independent approach that is exact up to the temperature dependence of the speed of sound in the broken phase. we find that the only relevant quantities that enter in the hydrodynamic analysis are the speed of sound in the broken phase and a linear combination of the energy and pressure differences between the two phases which we call pseudotrace (normalized to the enthalpy in the broken phase). the pseudotrace quantifies the strength of the phase transition and yields the conventional trace of the energy-momentum tensor for a relativistic plasma (with speed of sound squared of one third). we study this approach in several realistic models of the phase transition and also provide a code snippet that can be used to determine the efficiency coefficient for a given phase transition strength and speed of sound. it turns out that our approach is accurate to the percent level for moderately strong phase transitions, while former approaches give at best the right order of magnitude. | model-independent energy budget of cosmological first-order phase transitions—a sound argument to go beyond the bag model |
we propose an interferometric scheme based on an untrapped nano-object subjected to gravity. the motion of the center of mass (c.m.) of the free object is coupled to its internal spin system magnetically, and a free flight scheme is developed based on coherent spin control. the wave packet of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. a gravity induced dynamical phase (accrued solely on the spin state, and measured through a ramsey scheme) is used to reveal the above spatially delocalized superposition of the spin-nano-object composite system that arises during our scheme. we find a remarkable immunity to the motional noise in the c.m. (initially in a thermal state with moderate cooling), and also a dynamical decoupling nature of the scheme itself. together they secure a high visibility of the resulting ramsey fringes. the mass independence of our scheme makes it viable for a nano-object selected from an ensemble with a high mass variability. given these advantages, a quantum superposition with a 100 nm spatial separation for a massive object of 1 09 amu is achievable experimentally, providing a route to test postulated modifications of quantum theory such as continuous spontaneous localization. | free nano-object ramsey interferometry for large quantum superpositions |
plane gravitational waves can admit a sixth 'screw' isometry beyond the usual five. the same is true of plane electromagnetic waves. from the point of view of integrable systems, a sixth isometry would appear to over-constrain particle dynamics in such waves; we show here, though, that no effect of the sixth isometry is independent of those from the usual five. many properties of particle dynamics in a screw-symmetric gravitational wave are also seen in a (non-plane-wave) electromagnetic vortex; we make this connection explicit, showing that the screw-symmetric gravitational wave is the classical double copy of the vortex. | screw-symmetric gravitational waves: a double copy of the vortex |
taiji, a space-based gravitational-wave observatory, consists of three satellites forming an equilateral triangle with arm length of 3 ×106 km, orbiting around the sun. taiji is able to observe the gravitational-wave standard siren events of massive black hole binary (mbhb) merger, which is helpful in probing the expansion of the universe. in this paper, we preliminarily forecast the capability of taiji for improving cosmological parameter estimation with the gravitational-wave standard siren data. we simulate five-year standard siren data based on three fiducial cosmological models and three models of mbhb's formation and growth. it is found that the standard siren data from taiji can effectively break the cosmological parameter degeneracies generated by the cosmic microwave background (cmb) anisotropies data, especially for dynamical dark energy models. the constraints on cosmological parameters are significantly improved by the data combination cmb + taiji, compared to the cmb data alone. compared to the current optical cosmological observations, taiji can still provide help in improving the cosmological parameter estimation to some extent. in addition, we consider an ideal scenario to investigate the potential of taiji on constraining cosmological parameters. we conclude that the standard sirens of mbhb from taiji will become a powerful cosmological probe in the future. | prospects for improving cosmological parameter estimation with gravitational-wave standard sirens from taiji |
we report here the non-detection of gravitational waves from the merger of binary-neutron star systems and neutron star-black hole systems during the first observing run of the advanced laser interferometer gravitational-wave observatory (ligo). in particular, we searched for gravitational-wave signals from binary-neutron star systems with component masses \in [1,3] {m}⊙and component dimensionless spins <0.05. we also searched for neutron star-black hole systems with the same neutron star parameters, black hole mass \in [2,99] {m}⊙ , and no restriction on the black hole spin magnitude. we assess the sensitivity of the two ligo detectors to these systems and find that they could have detected the merger of binary-neutron star systems with component mass distributions of 1.35 ± 0.13 m ⊙ at a volume-weighted average distance of ∼70 mpc, and for neutron star-black hole systems with neutron star masses of 1.4 m ⊙ and black hole masses of at least 5 m ⊙, a volume-weighted average distance of at least ∼110 mpc. from this we constrain with 90% confidence the merger rate to be less than 12,600 gpc-3 yr-1 for binary-neutron star systems and less than 3600 gpc-3 yr-1 for neutron star-black hole systems. we discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. however, we find that if no detection of neutron star-binary mergers is made in the next two advanced ligo and advanced virgo observing runs we would place significant constraints on the merger rates. finally, assuming a rate of {10}-7+20 gpc-3 yr-1, short gamma-ray bursts beamed toward the earth, and assuming that all short gamma-ray bursts have binary-neutron star (neutron star-black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\buildrel{\circ}\over{.} {3}-1.1+1.7 (4\buildrel{\circ}\over{.} {3}-1.9+3.1). | upper limits on the rates of binary neutron star and neutron star-black hole mergers from advanced ligo’s first observing run |
we study the circularization of tidally disrupted stars on bound orbits around spinning supermassive black holes by performing 3d smoothed particle hydrodynamic simulations with post-newtonian corrections. our simulations reveal that debris circularization depends sensitively on the efficiency of radiative cooling. there are two stages in debris circularization if radiative cooling is inefficient: first, the stellar debris streams self-intersect due to relativistic apsidal precession; shocks at the intersection points thermalize orbital energy and the debris forms a geometrically thick, ring-like structure around the black hole. the ring rapidly spreads via viscous diffusion, leading to the formation of a geometrically thick accretion disc. in contrast, if radiative cooling is efficient, the stellar debris circularizes due to self-intersection shocks and forms a geometrically thin ring-like structure. in this case, the dissipated energy can be emitted during debris circularization as a precursor to the subsequent tidal disruption flare. the circularization time-scale is remarkably long in the radiatively efficient cooling case, and is also sensitive to black hole spin. specifically, lense-thirring torques cause dynamically important nodal precession, which significantly delays debris circularization. on the other hand, nodal precession is too slow to produce observable signatures in the radiatively inefficient case. since the stellar debris is optically thick and its photon diffusion time is likely longer than the time-scale of shock heating, our inefficient cooling scenario is more generally applicable in eccentric tidal disruption events (tdes). however, in parabolic tdes for mbh ≳ 2 × 106 m⊙, the spin-sensitive behaviour associated with efficient cooling may be realized. | circularization of tidally disrupted stars around spinning supermassive black holes |
we present new big bang nucleosynthesis (bbn) limits on the cosmic expansion rate or relativistic energy density, quantified via the number nν of equivalent neutrino species. we use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates d + d ⟶ 3he + n and d + d ⟶ 3h+ p. combining this result with the independent constraints from the cosmic microwave background (cmb) yields tight limits on new physics that perturbs nν and η prior to cosmic nucleosynthesis: a joint bbn+cmb analysis gives nν = 2.898 ± 0.141, resulting in nν < 3.180 at 2σ. we apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. the strength of the independent bbn and cmb constraints now opens a new window: we can search for limits on potential changes in nν and/or the baryon-to-photon ratio η between the two epochs. the present data place strong constraints on the allowed changes in nν between bbn and cmb decoupling; for example, we find -0.708 < nν cmb - nν bbn < 0.328 in the case where η and the primordial helium mass fraction yp are unchanged between the two epochs; we also give limits on the allowed variations in η or in (η, nν ) jointly. we discuss scenarios in which such changes could occur, and show that bbn+cmb results combine to place important constraints on some early dark energy models to explain the h0 tension. looking to the future, we forecast the tightened precision for nν arising from both cmb stage 4 measurements as well as improvements in astronomical 4he measurements. we find that cmb-s4 combined with present bbn and light element observation precision can give σ(nν ) ≃ 0.03. such future precision would reveal the expected effect of neutrino heating (neff -3 = 0.044) of the cmb during bbn, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model. improved yp measurements can push this precision even further. | probing physics beyond the standard model: limits from bbn and the cmb independently and combined |
skyportal is an open-source software package designed to discover interesting transients efficiently, manage follow-up, perform characterization, and visualize the results. by enabling fast access to archival and catalog data, crossmatching heterogeneous data streams, and the triggering and monitoring of on-demand observations for further characterization, a skyportal-based platform has been operating at scale for >2 yr for the zwicky transient facility phase ii community, with hundreds of users, containing tens of millions of time-domain sources, interacting with dozens of telescopes, and enabling community reporting. while skyportal emphasizes rich user experiences across common front-end workflows, recognizing that scientific inquiry is increasingly performed programmatically, skyportal also surfaces an extensive and well-documented application programming interface system. from back-end and front-end software to data science analysis tools and visualization frameworks, the skyportal design emphasizes the reuse and leveraging of best-in-class approaches, with a strong extensibility ethos. for instance, skyportal now leverages chatgpt large language models to generate and surface source-level human-readable summaries automatically. with the imminent restart of the next generation of gravitational-wave detectors, skyportal now also includes dedicated multimessenger features addressing the requirements of rapid multimessenger follow-up: multitelescope management, team/group organizing interfaces, and crossmatching of multimessenger data streams with time-domain optical surveys, with interfaces sufficiently intuitive for newcomers to the field. this paper focuses on the detailed implementations, capabilities, and early science results that establish skyportal as a community software package ready to take on the data science challenges and opportunities presented by this next chapter in the multimessenger era. | a data science platform to enable time-domain astronomy |
future gravitational-wave detectors operated at cryogenic temperatures are expected to be limited by thermal noise of the highly reflective mirror coatings. silicon nitride is an interesting material for such coatings as it shows very low mechanical loss, a property related to low thermal noise, which is known to further decrease under stress. low optical absorption is also required to maintain the low mirror temperature. here we investigate the effect of stress on the optical properties at 1550 nm of silicon nitride membranes attached to a silicon frame. our approach includes the measurement of the thermal expansion coefficient and the thermal conductivity of the membranes. the membrane and frame temperatures are varied, and translated into a change in stress using finite element modeling. the resulting product of the optical absorption and thermo-optic coefficient (dn/dt) is measured using photothermal common-path interferometry. | effect of stress and temperature on the optical properties of silicon nitride membranes at 1550nm |
this paper presents an algorithm to accelerate the evaluation of inspiral-merger-ringdown waveform models for gravitational wave data analysis. while the idea can also be applied in the time domain, here we focus on the frequency domain, which is most typically used to reduce computational cost in gravitational wave data analysis. our work extends the idea of multibanding vinciguerra s et al (2017 class. quantum grav. 34 115006), which has been developed to accelerate frequency domain waveforms, to include the merger and ringdown and spherical harmonics beyond the dominant quadrupole spherical harmonic. the original method of vinciguerra s et al (2017 class. quantum grav. 34 115006) is based on a heuristic algorithm based on the inspiral to de-refine the equi-spaced frequency grid used for data analysis where a coarser grid is sufficient for accurate evaluation of a waveform model. here we use a different criterion, based on the local interpolation error, which is more flexible and can easily be adapted to general waveforms, if their phenomenology is understood. we discuss our implementation in the ligo algorithms library (the ligo scientific collaboration 2015 https://lsc-group.phys.uwm.edu/daswg/projects/lalsuite.html) for the imrphenomxhm garcía quirós c et al (2020 arxiv:2001.10914) frequency domain model, and report the acceleration in different parts of the parameter space of compact binary systems. | accelerating the evaluation of inspiral-merger-ringdown waveforms with adapted grids |
upcoming searches for the stochastic background of inflationary gravitational waves (gws) offer the exciting possibility to probe the evolution of our universe prior to big bang nucleosynthesis. in this spirit, we explore the sensitivity of future gw observations to a broad class of beyond-the-standard-model scenarios that lead to a nonstandard expansion history. we consider a new scalar field whose coherent oscillations dominate the energy density of the universe at very early times, resulting in a scalar era prior to the standard radiation-dominated era. the imprint of this scalar era on the primordial gw spectrum provides a means to probe well-motivated yet elusive models of particle physics. our work highlights the complementarity of future gw observatories across the entire range of accessible frequencies. | imprint of a scalar era on the primordial spectrum of gravitational waves |
we provide an easy method to obtain the kinetic energy fraction in gravitational waves, generated during a cosmological first-order phase transition, as a function of only the wall velocity and quantities that can be determined from the particle physics model at the nucleation temperature. this generalizes recent work that achieved this goal for detonations. here we present the corresponding results for deflagrations and hybrids. unlike for detonations, the sound speed in the symmetric phase also enters the analysis. we perform a detailed comparison between our model-independent approach and other approaches in the literature. we provide a python code snippet to determine the kinetic energy fraction k as a function of the wall velocity, the two speeds of sound and the strength parameter of the phase transition. we also assess how realistic sizable deviations in speed of sound are close to the phase transition temperature in a specific model. | model-independent energy budget for lisa |
models with singlet fields coupling to the higgs can enable a strongly first-order electroweak phase transition, of interest for baryogenesis and gravity waves. we improve on previous attempts to self-consistently solve for the bubble wall properties—wall speed vw and shape—in a highly predictive class of models with z2-symmetric singlet potentials. a new algorithm is implemented to determine vw and the wall profiles throughout the singlet parameter space in the case of subsonic walls, focusing on models with strong enough phase transitions to satisfy the sphaleron washout constraint for electroweak baryogenesis. we find speeds as low as vw≅0.1 in our scan over parameter space, and the singlet must be relatively light to have a subsonic wall, ms≲135 gev . | wall speed and shape in singlet-assisted strong electroweak phase transitions |
an advanced ligo and virgo's third observing run brought another binary neutron star merger (bns) and the first neutron-star black hole mergers. while no confirmed kilonovae were identified in conjunction with any of these events, continued improvements of analyses surrounding gw170817 allow us to project constraints on the hubble constant (h 0), the galactic enrichment from r-process nucleosynthesis, and ultra-dense matter possible from forthcoming events. here, we describe the expected constraints based on the latest expected event rates from the international gravitational-wave network and analyses of gw170817. we show the expected detection rate of gravitational waves and their counterparts, as well as how sensitive potential constraints are to the observed numbers of counterparts. we intend this analysis as support for the community when creating scientifically driven electromagnetic follow-up proposals. during the next observing run o4, we predict an annual detection rate of electromagnetic counterparts from bns of ${0.43}_{-0.26}^{+0.58}$ ( ${1.97}_{-1.2}^{+2.68}$ ) for the zwicky transient facility (rubin observatory). | updated observing scenarios and multimessenger implications for the international gravitational-wave networks o4 and o5 |
the detection of orbital eccentricity for a binary black hole system via gravitational waves is a key signature to distinguish between the possible binary origins. the identification of eccentricity has been difficult so far due to the limited availability of eccentric gravitational waveforms over the full range of black hole masses and eccentricities. here we evaluate the eccentricity of five black hole mergers detected by the ligo and virgo observatories for the first time using the teobresumsgeneral model. this model accounts for the full eccentricity range possible and incorporates higher-order gravitational wave modes critical to model emission from highly eccentric orbits. the binaries have been selected due to previous hints of eccentricity or due to their unusual mass and spin. while other studies found marginal evidence for eccentricity for some of these events, our analyses do not favor the incorporation of eccentricity compared to the quasi-circular case. while lacking the eccentric evidence of other analyses, we find our analyses marginally shifts the posterior in multiple parameters for several events when allowing eccentricity to be non-zero. | eccentricity estimation for five binary black hole mergers with higher-order gravitational wave modes |
we formulate and experimentally validate a set of spin-momentum equations which are analogous to the maxwell's equations and govern spin-orbit coupling in electromagnetic guided waves. the maxwell-like spin-momentum equations reveal the spin-momentum locking, the chiral spin texture of the field, berry phase, and the spin-orbit interaction in the optical near field. the observed spin-momentum behavior can be extended to other classical waves, such as acoustic, fluid, gas, and gravitational waves. | transverse spin dynamics in structured electromagnetic guided waves |
we discuss effects of loss of coherence in low energy quantum systems caused by or related to gravitation, referred to as gravitational decoherence. these effects, resulting from random metric fluctuations, for instance, promise to be accessible by relatively inexpensive table-top experiments, way before the scales where true quantum gravity effects become important. therefore, they can provide a first experimental view on gravity in the quantum regime. we will survey models of decoherence induced both by classical and quantum gravitational fluctuations; it will be manifest that a clear understanding of gravitational decoherence is still lacking. next we will review models where quantum theory is modified, under the assumption that gravity causes the collapse of the wave functions, when systems are large enough. these models challenge the quantum-gravity interplay, and can be tested experimentally. in the last part we have a look at the state of the art of experimental research. we will review efforts aiming at more and more accurate measurements of gravity (g and g) and ideas for measuring conventional and unconventional gravity effects on nonrelativistic quantum systems. | gravitational decoherence |
gravitational waves emitted by distorted black holes—such as those arising from the coalescence of two neutron stars or black holes—carry not only information about the corresponding spacetime but also about the underlying theory of gravity. although general relativity remains the simplest, most elegant, and viable theory of gravitation, there are generic and robust arguments indicating that it is not the ultimate description of the gravitational universe. here, we focus on a particularly appealing extension of general relativity, which corrects einstein's theory through the addition of terms which are second order in curvature: the topological gauss-bonnet invariant coupled to a dilaton. we study gravitational-wave emission from black holes in this theory and (i) find strong evidence that black holes are linearly (mode) stable against both axial and polar perturbations, (ii) discuss how the quasinormal modes of black holes can be excited during collisions involving black holes, and finally (iii) show that future ringdown detections with a large signal-to-noise ratio would improve current constraints on the coupling parameter of the theory. | perturbed black holes in einstein-dilaton-gauss-bonnet gravity: stability, ringdown, and gravitational-wave emission |
one unanswered question about the binary neutron star coalescence gw170817 is the nature of its post-merger remnant. a previous search for post-merger gravitational waves targeted high-frequency signals from a possible neutron star remnant with a maximum signal duration of 500 s. here, we revisit the neutron star remnant scenario and focus on longer signal durations, up until the end of the second advanced ligo-virgo observing run, which was 8.5 days after the coalescence of gw170817. the main physical scenario for this emission is the power-law spindown of a massive magnetar-like remnant. we use four independent search algorithms with varying degrees of restrictiveness on the signal waveform and different ways of dealing with noise artefacts. in agreement with theoretical estimates, we find no significant signal candidates. through simulated signals, we quantify that with the current detector sensitivity, nowhere in the studied parameter space are we sensitive to a signal from more than 1 mpc away, compared to the actual distance of 40 mpc. however, this study serves as a prototype for post-merger analyses in future observing runs with expected higher sensitivity. | search for gravitational waves from a long-lived remnant of the binary neutron star merger gw170817 |
we calculate the spectrum of gravitational waves originated from strongly first order electroweak phase transition in the extended higgs model with a real singlet scalar field. in order to calculate the bubble nucleation rate, we perform a two-field analysis and evaluate bounce solutions connecting the true and the false vacua using the one-loop effective potential at finite temperatures. imposing the sakharov condition of the departure from thermal equilibrium for baryogenesis, we survey allowed regions of parameters of the model. we then investigate the gravitational waves produced at electroweak bubble collisions in the early universe, such as the sound wave, the bubble wall collision and the plasma turbulence. we find that the strength at the peak frequency can be large enough to be detected at future space-based gravitational interferometers such as elisa, decigo and bbo. predicted deviations in the various higgs boson couplings are also evaluated at the zero temperature, and are shown to be large enough too. therefore, in this model strongly first order electroweak phase transition can be tested by the combination of the precision study of various higgs boson couplings at the lhc, the measurement of the triple higgs boson coupling at future lepton colliders and the shape of the spectrum of gravitational wave detectable at future gravitational interferometers. | gravitational waves and higgs boson couplings for exploring first order phase transition in the model with a singlet scalar field |
the speed of sound of the matter within neutron stars may contain nonsmooth structure related to first- or higher-order phase transitions. here we investigate what are the observable consequences of structure in the speed of sound, such as bumps, spikes, step functions, plateaus, and kinks. one of the main consequences is the possibility of ultraheavy neutron stars (with masses larger than 2.5 solar masses), mass twins in heavy (with masses larger than 2 solar masses) and ultraheavy neutron stars. these stars pass all observational and theoretical constraints, including those imposed by recent ligo/virgo gravitational-wave observations and nicer x-ray observations. we thoroughly investigate other consequences of this structure in the speed of sound to develop an understanding of how nonsmooth features affect astrophysical observables, such as stellar radii, tidal deformability, moment of inertia, and love number. our results have important implications for future gravitational wave and x-ray observations of neutron stars and their impact in nuclear astrophysics. | extreme matter meets extreme gravity: ultraheavy neutron stars with phase transitions |
the next generation of cosmic microwave background, gravitational wave, and large scale structure, experiments will provide an unprecedented opportunity to probe the primordial power spectrum on small scales. an exciting possibility for what lurks on small scales is a sharp rise in the primordial power spectrum: this can lead to the formation of primordial black holes, providing a dark matter candidate or the black holes observed by the ligo-virgo collaboration. in this work we develop a mechanism for the amplification of the small-scale primordial power spectrum, in the context of single-field inflation with a step-like feature in the inflaton potential. specifically, we consider both the upward and the downward step in the potential. we also discuss the possibility of the strong coupling between perturbations because the rapid changes of the potential derivatives with the time-dependent field value, caused by the step-like feature, could make the coupling stronger. as a result, we find that the perturbations can remain weakly coupled yet sufficiently enhanced if the step realizes the rapid changes of the potential derivatives in some fraction of an e-fold, 𝒪(𝒫ℛ 1/2) ≲ δn < 1, where 𝒫ℛ is the power spectrum of the curvature perturbation at that time. we also discuss the pbh formation rate from the inflaton trapping at the local minimum, which can occur in the potential with an upward step. | amplification of primordial perturbations from the rise or fall of the inflaton |
kilonovae are ultraviolet, optical, and infrared transients powered by the radioactive decay of heavy elements following a neutron star merger. joint observations of kilonovae and gravitational waves can offer key constraints on the source of galactic r-process enrichment, among other astrophysical topics. however, robust constraints on heavy element production require rapid kilonova detection (within ~1 day of merger) as well as multiwavelength observations across multiple epochs. in this study, we quantify the ability of 13 wide-field-of-view instruments to detect kilonovae, leveraging a large grid of over 900 radiative transfer simulations with 54 viewing angles per simulation. we consider both current and upcoming instruments, collectively spanning the full kilonova spectrum. the roman space telescope has the highest redshift reach of any instrument in the study, observing kilonovae out to z ~ 1 within the first day post-merger. we demonstrate that blackgem, decam, goto, the vera c. rubin observatory's lsst, ultrasat, vista, and winter can observe some kilonovae out to z ~ 0.1 (~475 mpc), while ddoti, meerlicht, prime, swift/uvot, and ztf are confined to more nearby observations. furthermore, we provide a framework to infer kilonova ejecta properties following nondetections and explore variation in detectability with these ejecta parameters. | kilonova detectability with wide-field instruments |
the statistical characteristics of inertia-gravity waves (igws) in the troposphere (2-14 km) and lower stratosphere (18-28 km) are analyzed using daily radiosonde observations over six stations in the western pacific from 2013 to 2018. stokes parameter method is used to extract the characteristic parameters of gravity waves (gws), which are divided into upward and downward propagating waves, and compared with the results of hodograph analysis. in the stratosphere, due to the filtering effect of the background wind field, the igws generated in the troposphere mainly propagate eastward with lower frequency range. the tropospheric igws have obvious seasonal variation in spectral amplitude and energy, with the maximum in winter and the minimum in monsoon from 2013 to 2018. the stratospheric igws are enhanced during phase transition of the quasi-biennial oscillation, when the enhanced easterly wind appears in the lowest stratosphere, accompanied by enhanced wave energy in the troposphere. during the quasi-biennial oscillation disruption in late 2015 and early 2016, the tropospheric wave source excites more intense igws propagating upward. after reaching the stratosphere, igws with slower phase speed are absorbed by the mean flow, dissipating momentum to the lower stratosphere and generating additional enhanced westward forcing, which may have contributed to the development of the easterly wind within the westerly quasi-biannual oscillation phase. | observations of inertia gravity waves in the western pacific and their characteristic in the 2015/2016 quasi-biennial oscillation disruption |
the european variscan belt is a unique orogen that is covered by comprehensive sets of seismic and potential field data from the iberian peninsula in the west to the polish sudetes in the east. the combination of both allows for a new interpretation of the structure and evolution of the european variscides at the continental scale. the european variscan belt has been divided into three domains according to distinct geological and geophysical characteristics: 1) the north-eastern variscan domain (nvd) outcropping in the bohemian massif, black forest and vosges massifs, and the rhenish massif, 2) the central variscan domain (cvd) represented by the french massif central, armorican massif and british variscides, and 3) the south-western variscan domain (svd) represented by the iberian massif. the gravity data show the presence of high amplitude, short-wavelength gravity anomalies that are mainly correlated with the outcrops of eclogites, ultramafic rocks and ophiolites. these anomalies locate the main body of the mid-variscan allochthon in the svd and cvd and the devonian mid-variscan suture in the nvd. the gravity data also show medium amplitude elongated long-wavelength gravity highs aligned parallel to the structural grain of the variscan belt, represented by the deformed teplá-barrandian-kraichgau upper crustal rocks, a devonian supra-subduction basin in the mid-variscan allochthon, and the autochthonous rocks of the central iberian zone in the svd, the armorican massif in the cvd and the saxothuringian zone in the nvd. the short wavelength negative gravity anomalies are mainly developed in the central part of the belt and coincide with carboniferous (330-310 ma) per- to meta-aluminous magmatic bodies, pre-variscan orthogneisses and carboniferous felsic granulite bodies. noticeably, permian (300-290 ma) granitoids do not reveal any gravity lows indicating that these bodies are not deeply rooted. the magnetic data show two belts correlated to carboniferous rhenohercynian and devonian mid-variscan magmatic arc granitoids. the rhenohercynian and mid-variscan subduction systems are well imaged by moderately se dipping primary a-type reflectors in reflection seismic lines in the nvd and cvd, while in the svd the reflectors related to the rhenohercynian subduction are dipping to the ne and the seismic signature of the mid-variscan suture is weakly developed. in the nvd, a third belt of se-dipping reflectors is attributed to the carboniferous subduction of the saxothuringian continental lithosphere beneath the mid-variscan allochthon. younger b-type moderately dipping reflectors in the upper-middle crust coincide with outcrops of carboniferous detachments, sometimes limiting granite plutons and core complexes along-strike the core of the variscan orogeny. c-type reflectors occur mainly in the deep crust and are considered as an expression of lower crustal flow resulting from extensional re-equilibration of the previously thickened variscan crust. a synthesis of p-wave velocity logs at the scale of the whole variscan belt shows the existence of three different continental crusts: (i) cratonic crust marked by a thick, high velocity lower crust, (ii) transitional crust characterised by a relatively thin high velocity lower crust and intermediate velocity middle crust, and (iii) a thin variscan orogenic crust defined by low velocity lower and middle crust. the latter crustal type coincides with regional outcrops of 330-310 ma per- to meta- aluminous granitoids and associated gravity lows along-strike the belt. it is argued that the specific "variscan" orogenic crust originated by carboniferous extensional thinning and extensive melting of previously thickened "tibetan" type crust and not from permian tectogenesis, which is restricted to marginal parts of the orogen. | tectonic evolution and global crustal architecture of the european variscan belt constrained by geophysical data |
the mirror twin higgs model is a candidate for (strongly-interacting) complex dark matter, which mirrors sm interactions with heavier quark masses. a consequence of this model are mirror neutron stars—exotic stars made entirely of mirror matter, which are significantly smaller than neutron stars and electromagnetically dark. this makes mergers of two mirror neutron stars detectable and distinguishable in gravitational wave observations, but can we observationally distinguish between regular neutron stars and those that may contain some mirror matter? this is the question we study in this paper, focusing on two possible realizations of mirror matter coupled to standard model matter within a compact object: (i) mirror matter captured by a neutron star and (ii) mirror neutron star-neutron star coalescences. regarding (i), we find that (nonrotating) mirror-matter-admixed neutron stars no longer have a single mass-radius sequence, but rather exist in a two-dimensional mass-radius plane. regarding (ii), we find that binary systems with mirror neutron stars would span a much wider range of chirp masses and completely different binary love relations, allowing merger remnants to be very light black holes. the implications of this are that gravitational wave observations with advanced ligo and virgo, and x-ray observations with nicer, could detect or constrain the existence of mirror matter through searches with wider model and parameter priors. | dark matter or regular matter in neutron stars? how to tell the difference from the coalescence of compact objects |
we have investigated the systematic differences introduced when performing a bayesian-inference analysis of the equation of state (eos) of neutron stars employing either variable- or constant-likelihood functions. the former has the advantage of retaining the full information on the distributions of the measurements, making exhaustive usage of the data. the latter, on the other hand, has the advantage of a much simpler implementation and reduced computational costs. in both approaches, the eoss have identical priors and have been built using the sound speed parameterization method so as to satisfy the constraints from x-ray and gravitational waves observations, as well as those from chiral effective theory and perturbative quantum chromodynamics. in all cases, the two approaches lead to very similar results and the 90% confidence levels essentially overlap. some differences do appear, but in regions where the probability density is extremely small and are mostly due to the sharp cutoff on the binary tidal deformability $\tilde{{\rm{\lambda }}}\leqslant 720$ set in the constant-likelihood approach. our analysis has also produced two additional results. first, an inverse correlation between the normalized central number density, nc,tov/ns , and the radius of a maximally massive star, r tov. second, and most importantly, it has confirmed the relation between the chirp mass and the binary tidal deformability. the importance of this result is that it relates ${{ \mathcal m }}_{\mathrm{chirp}}$ , which is measured very accurately, and $\tilde{{\rm{\lambda }}}$ , which contains important information on the eos. hence, when ${{ \mathcal m }}_{\mathrm{chirp}}$ is measured in future detections, our relation can be used to set tight constraints on $\tilde{{\rm{\lambda }}}$ . | bayesian analysis of neutron-star properties with parameterized equations of state: the role of the likelihood functions |
two neutron stars merge somewhere in the universe approximately every 10 to 100 s, creating violent explosions potentially observable in gravitational waves and across the electromagnetic spectrum. the transformative coincident gravitational-wave and electromagnetic observations of the binary neutron star merger gw170817 gave invaluable insights into these cataclysmic collisions, probing bulk nuclear matter at supranuclear densities, the jet structure of gamma-ray bursts, the speed of gravity, and the cosmological evolution of the local universe, among other things. despite the wealth of information, it is still unclear when the remnant of gw170817 collapsed to form a black hole. evidence from other short gamma-ray bursts indicates a large fraction of mergers may form long-lived neutron stars. we review what is known observationally and theoretically about binary neutron star post-merger remnants. from a theoretical perspective, we review our understanding of the evolution of short- and long-lived merger remnants, including fluid, magnetic-field, and temperature evolution. these considerations impact prospects of detection of gravitational waves from either short- or long-lived neutron star remnants which potentially allows for new probes into the hot nuclear equation of state in conditions inaccessible in terrestrial experiments. we also review prospects for determining post-merger physics from current and future electromagnetic observations, including kilonovae and late-time x-ray and radio afterglow observations. | the evolution of binary neutron star post-merger remnants: a review |
hydrodynamics provides a universal description of interacting quantum field theories at sufficiently long times and wavelengths, but breaks down at scales dependent on microscopic details of the theory. in the vicinity of a quantum critical point, it is expected that some aspects of the dynamics are universal and dictated by properties of the critical point. we use gauge-gravity duality to investigate the breakdown of diffusive hydrodynamics in two low-temperature states dual to black holes with ads2 horizons, which exhibit quantum critical dynamics with an emergent scaling symmetry in time. we find that the breakdown is characterized by a collision between the diffusive pole of the retarded green's function with a pole associated to the ads2 region of the geometry, such that the local equilibration time is set by infrared properties of the theory. the absolute values of the frequency and wave vector at the collision (ωeq and keq) provide a natural characterization of all the low-temperature diffusivities d of the states via d =ωeq/keq2, where ωeq=2 π δ t is set by the temperature t and the scaling dimension δ of an operator of the infrared quantum critical theory. we confirm that these relations are also satisfied in a sachdev-ye-kitaev chain model in the limit of strong interactions. our work paves the way toward a deeper understanding of transport in quantum critical phases. | hydrodynamic diffusion and its breakdown near ads2 quantum critical points |
we confirm the generalized actions of the complete nlo cubic-in-spin interactions for generic compact binaries which were first tackled via an extension of the eft of spinning gravitating objects. we first reduce these generalized actions to standard actions with spins, where the interaction potentials are found to consist of 6 independent sectors, including a new unique sector that is proportional to the square of the quadrupolar deformation parameter, ces2. we derive the general hamiltonians in an arbitrary reference frame, and for generic kinematic configurations. with these most general hamiltonians we construct the full poincaré algebra of all the sectors at the fourth and a half post-newtonian (4.5pn) order, including the third subleading spin-orbit sector, recently accomplished uniquely via our framework, thus proving the poincaré invariance of all relevant sectors. we then derive the binding energies with gauge-invariant relations useful for gravitational-wave applications. finally, we also derive the extrapolated scattering angles in the aligned-spins configuration for the scattering problem. yet, as made clear already as of quadratic-in-spin sectors, the aligned-spins simplification inherent to the scattering-angle observable, entails a great loss of physical information, that is only growing with higher-spin sectors. our completion of the full poincaré algebra at the present 4.5pn order provides strong confidence that this new precision frontier in pn theory has now been established. | from the eft of spinning gravitating objects to poincaré and gauge invariance at the 4.5pn precision frontier |
by extending our recent framework to describe the tidal deformations of a spinning compact object, we compute for the first time the tidal love numbers of a spinning neutron star to linear order in the angular momentum. the spin of the object introduces couplings between electric and magnetic distortions, and new classes of spin-induced ("rotational") tidal love numbers emerge. we focus on stationary tidal fields, which induce axisymmetric perturbations. we present the perturbation equations for both electric-led and magnetic-led rotational love numbers for generic multipoles and explicitly solve them for various tabulated equations of state and for a tidal field with an electric (even parity) and magnetic (odd parity) component with ℓ=2 , 3, 4. for a binary system close to the merger, various components of the tidal field become relevant. in this case we find that an octupolar magnetic tidal field can significantly modify the mass quadrupole moment of a neutron star. preliminary estimates, assuming a spin parameter χ ≈0.05 , show modifications ≳10 % relative to the static case, at an orbital distance of five stellar radii. furthermore, the rotational love numbers as functions of the moment of inertia are much more sensitive to the equation of state than in the static case, where approximate universal relations at the percent level exist. for a neutron-star binary approaching the merger, we estimate that the approximate universality of the induced mass quadrupole moment deteriorates from 1% in the static case to roughly 6% when χ ≈0.05 . our results suggest that spin-tidal couplings can introduce important corrections to the gravitational waveforms of spinning neutron-star binaries approaching the merger. | tidal love numbers of a slowly spinning neutron star |
future gravitational wave interferometers such as the laser interferometer space antenna, taiji, deci-hertz interferometer gravitational wave observatory and tianqin will enable precision studies of the environment surrounding black holes. these detectors will probe the millihertz frequency range, as yet unexplored by current gravitational wave detectors. furthermore, sources will remain in band for durations of up to years, meaning that the inspiral phase of the gravitational wave signal, which can be affected by the environment, will be observable. in this paper, we study intermediate and extreme mass ratio binary black hole inspirals, and consider three possible environments surrounding the primary black hole: accretion disks, dark matter spikes and clouds of ultra-light scalar fields, also known as gravitational atoms. we present a bayesian analysis of the detectability and measurability of these three environments. focusing for concreteness on the case of a detection with lisa, we show that the characteristic imprint they leave on the gravitational waveform would allow us to identify the environment that generated the signal and to accurately reconstruct its model parameters. | distinguishing environmental effects on binary black hole gravitational waveforms |
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