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we investigate a new property of retarded green's functions using ads/cft. the green's functions are not unique at special points in complex momentum space. this arises because there is no unique incoming mode at the horizon and is similar to the "pole-skipping" phenomenon in holographic chaos. our examples include the bulk scalar field, the bulk maxwell vector and scalar modes, and the shear mode of gravitational perturbations. in these examples, the special points are always located at 𝜔★ = -i(2πt) with appropriate values of complex wave number. | nonuniqueness of green's functions at special points |
in this paper, we study the strong gravitational lensing of gravitational waves (gws) from a statistical perspective, with particular focus on the high frequency gws from stellar binary black hole coalescences. these are most promising targets for ground-based detectors such as advanced laser interferometer gravitational wave observatory (aligo) and the proposed einstein telescope (et) and can be safely treated under the geometrical optics limit for gw propagation. we perform a thorough calculation of the lensing rate, by taking account of effects caused by the ellipticity of lensing galaxies, lens environments, and magnification bias. we find that in certain gw source rate scenarios, we should be able to observe strongly lensed gw events once per year (∼1 yr-1) in the aligo survey at its design sensitivity; for the proposed et survey, the rate could be as high as ∼80 yr-1. these results depend on the estimate of gw source abundance, and hence can be correspondingly modified with an improvement in our understanding of the merger rate of stellar binary black holes. we also compute the fraction of four-image lens systems in each survey, predicting it to be ∼30 per cent for the aligo survey and ∼6 per cent for the et survey. finally, we evaluate the possibility of missing some images due to the finite survey duration, by presenting the probability distribution of lensing time delays. we predict that this selection bias will be insignificant in future gw surveys, as most of the lens systems ({∼ } 90{per cent}) will have time delays less than ∼1 month, which will be far shorter than survey durations. | gravitational lensing of gravitational waves: a statistical perspective |
sinusoidal bloch oscillations appear in band structures exposed to external fields. landau-zener (lz) tunneling between different bands is usually a counteracting effect limiting bloch oscillations. here we consider a flat band network with two dispersive and one flat band, e.g., for ultracold atoms and optical waveguide networks. using external synthetic gauge and gravitational fields we obtain a perturbed yet gapless band structure with almost flat parts. the resulting bloch oscillations consist of two parts—a fast scan through the nonflat part of the dispersion structure, and an almost complete halt for substantial time when the atomic or photonic wave packet is trapped in the original flat band part of the unperturbed spectrum, made possible due to lz tunneling. | landau-zener bloch oscillations with perturbed flat bands |
young dense massive star clusters are promising environments for the formation of intermediate mass black holes (imbhs) through collisions. we present a set of 80 simulations carried out with nbody6++gpu of 10 models of compact $\sim 7 \times 10^4 \, \mathrm{m}_{\odot }$ star clusters with half-mass radii rh ≲ 1 pc, central densities $\rho _\mathrm{core} \gtrsim 10^5 \, \mathrm{m}_\odot \, \mathrm{pc}^{-3}$ , and resolved stellar populations with 10 per cent primordial binaries. very massive stars (vmss) up to $\sim 400 \, \mathrm{m}_\odot$ grow rapidly by binary exchange and three-body scattering with stars in hard binaries. assuming that in vms-stellar black hole (bh) collisions all stellar material is accreted on to the bh, imbhs with masses up to $m_\mathrm{bh} \sim 350 \, \mathrm{m}_\odot$ can form on time-scales of ≲15 myr, as qualitatively predicted from monte carlo mocca simulations. one model forms an imbh of 140 $\mathrm{m_{\odot }}$ by three bh mergers with masses of 17:28, 25:45, and 68:70 $\mathrm{m_{\odot }}$ within ∼90 myr. despite the stochastic nature of the process, formation efficiencies are higher in more compact clusters. lower accretion fractions of 0.5 also result in imbh formation. the process might fail for values as low as 0.1. the imbhs can merge with stellar mass bhs in intermediate mass ratio inspiral events on a 100 myr time-scale. with 105 stars, 10 per cent binaries, stellar evolution, all relevant dynamical processes, and 300 myr simulation time, our large suite of 80 simulations indicate another rapid imbh formation channel in young and compact massive star clusters. | intermediate mass black hole formation in compact young massive star clusters |
we study the imprints of new ultralight particles on the gravitational-wave signals emitted by binary black holes. superradiant instabilities may create large clouds of scalar or vector fields around rotating black holes. the presence of a binary companion then induces transitions between different states of the cloud, which become resonantly enhanced when the orbital frequency matches the energy gap between the states. we find that the time dependence of the orbit significantly impacts the cloud's dynamics during a transition. following an analogy with particle colliders, we introduce an s -matrix formalism to describe the evolution through multiple resonances. we show that the state of the cloud, as it approaches the merger, carries vital information about its spectrum via time-dependent finite-size effects. moreover, due to the transfer of energy and angular momentum between the cloud and the orbit, a dephasing of the gravitational-wave signal can occur, which is correlated with the positions of the resonances. notably, for intermediate and extreme mass ratio inspirals, long-lived floating orbits are possible, as well as kicks that yield large eccentricities. observing these effects, through the precise reconstruction of waveforms, has the potential to unravel the internal structure of the boson clouds, ultimately probing the masses and spins of new particles. | gravitational collider physics |
kagra is a newly build gravitational wave observatory, a laser interferometer with 3 km arm length, located in kamioka, gifu, japan. in this paper, one of a series of articles featuring kagra, we discuss the science targets of kagra projects, considering not only the baseline kagra (current design) but also its future upgrade candidates (kagra+) for the near to middle term ($\sim$5 years). | overview of kagra: kagra science |
we perform a search for binary black hole mergers with one subsolar mass black hole and a primary component above $2 m_\odot$ in the second observing run of ligo/virgo. our analysis therefore extends previous searches into a mass region motivated by the presence of a peak in any broad mass distribution of primordial black holes (pbhs) around $[2-3] m_\odot$ coming from the equation of state reduction at the qcd transition. four candidate events are found passing a false alarm rate (far) threshold of 2 per year, although none are statistically significant enough for being clear detections. we first derive model independent limits on the pbh merging rates assuming a null result of the search. then we confront them to two recent scenarios in which pbhs can constitute up to the totality of the dark matter, explain ligo/virgo mergers and the possible observation of a stochastic gravitational-wave background by nanograv. we find that these models still pass the rate limits and conclude that the analysis of the o3 and o4 observing runs will be decisive to test the hypothesis of a primordial origin of black hole mergers. | the hunt for sub-solar primordial black holes in low mass ratio binaries is open |
the propagation of meteorological drought in a complete water cycle is not limited to hydrological and agricultural droughts, but also involves groundwater drought. moreover, the intensification of water cycle under the background of global warming may also affect the time of drought propagation. therefore, studying the dynamic propagation and possible influence factors from meteorological to groundwater drought is helpful to monitor and assess the risk of groundwater drought. here we use terrestrial water storage anomalies observations from the gravity recovery and climate experiment satellites and simulated soil moisture and runoff variations from the global land data assimilation system to show that the groundwater storage anomalies in the pearl river basin (prb). the standardized precipitation index and drought severity index were used to characterize meteorological and groundwater drought, respectively. results indicated that: (1) the propagation time of meteorological to groundwater drought in the prb during 2002-2015 was 8 months, and that in spring and summer was shorter than that in autumn and winter; (2) the time of drought propagation has a significant deceasing trend (p < 0.01), indicating that the water cycle in the prb was accelerating; (3) increasing soil moisture accelerates the response of groundwater to precipitation in the surplus period due to the stored-full runoff mechanism, whilst intensifying evapotranspiration rate and heat wave facilitate the drought propagation in the deficit period; (4) compared with arctic oscillation and el-niño southern oscillation, pacific decadal oscillation is the main driving force to accelerate drought propagation in the prb. | propagation dynamics from meteorological to groundwater drought and their possible influence factors |
we describe the public release of the cluster monte carlo (cmc) code, a parallel, star-by-star n-body code for modeling dense star clusters. cmc treats collisional stellar dynamics using hénon's method, where the cumulative effect of many two-body encounters is statistically reproduced as a single effective encounter between nearest-neighbor particles on a relaxation timescale. the star-by-star approach allows for the inclusion of additional physics, including strong gravitational three- and four-body encounters, two-body tidal and gravitational-wave captures, mass loss in arbitrary galactic tidal fields, and stellar evolution for both single and binary stars. the public release of cmc is pinned directly to the cosmic population synthesis code, allowing dynamical star cluster simulations and population synthesis studies to be performed using identical assumptions about the stellar physics and initial conditions. as a demonstration, we present two examples of star cluster modeling: first, we perform the largest (n = 108) star-by-star n-body simulation of a plummer sphere evolving to core collapse, reproducing the expected self-similar density profile over more than 15 orders of magnitude; second, we generate realistic models for typical globular clusters, and we show that their dynamical evolution can produce significant numbers of black hole mergers with masses greater than those produced from isolated binary evolution (such as gw190521, a recently reported merger with component masses in the pulsational pair-instability mass gap). | modeling dense star clusters in the milky way and beyond with the cluster monte carlo code |
the next generation ground-based gravitational wave interferometers will possibly observe mergers of binary black holes (bbhs) and binary neutron stars (bnss) to redshift z ≳ 10 and ≳ 2, respectively. here, we characterize the properties of merging bbhs, bnss, and neutron star-black hole binaries across cosmic time, by means of population-synthesis simulations combined with the illustris cosmological simulation. we find that the mass of merging compact objects does not depend (or depends very mildly) on the merger redshift. even the mass distribution of black holes (bhs) depends only mildly on redshift, because bbhs originating from metal-poor progenitors (z ≤ 4 × 10-3) dominate the entire population of merging bbhs across cosmic time. for a common-envelope efficiency α ≥ 3, the main difference between the mass distribution of bbhs merging in the last gyr and that of bbhs merging more than 11 gyr ago is that there is an excess of heavy merging bhs (20-35 m⊙) in the last gyr. this excess is explained by the longer delay time of massive bbhs. | the properties of merging black holes and neutron stars across cosmic time |
extending previous work by a number of authors, we have recently presented a new approach in which the detection of gravitational waves from merging neutron star binaries can be used to determine the equation of state of matter at nuclear density and hence the structure of neutron stars. in particular, after performing a large number of numerical-relativity simulations of binaries with nuclear equations of state, we have found that the post-merger emission is characterized by two distinct and robust spectral features. while the high-frequency peak was already shown to be associated with the oscillations of the hypermassive neutron star produced by the merger and to depend on the equation of state, we have highlighted that the low-frequency peak is related to the merger process and to the total compactness of the stars in the binary. this relation is essentially universal and provides a powerful tool to set tight constraints on the equation of state. we here provide additional information on the extensive analysis performed, illustrating the methods used, the tests considered, as well as the robustness of the results. we also discuss additional relations that can be deduced when exploring the data and how these correlate with various properties of the binary. finally, we present a simple mechanical toy model that explains the main spectral features of the post-merger signal and can even reproduce analytically the complex waveforms emitted right after the merger. | spectral properties of the post-merger gravitational-wave signal from binary neutron stars |
we study the merger of binary neutron stars with different mass ratios adopting three different realistic, microphysical nuclear equations of state, as well as incorporating neutrino cooling effects. in particular, we concentrate on the influence of the equation of state on the gravitational wave signature and also on its role, in combination with neutrino cooling, in determining the properties of the resulting hypermassive neutron star, of the neutrinos produced, and of the ejected material. the ejecta we find are consistent with other recent studies that find that small mass ratios produce more ejecta than equal mass cases (up to some limit) and this ejecta is more neutron rich. this trend indicates the importance with future kilonovae observations of measuring the individual masses of an associated binary neutron star system, presumably from concurrent gravitational wave observations, in order to be able to extract information about the nuclear equation of state. | unequal mass binary neutron star mergers and multimessenger signals |
stellar-remnant black holes (bh) in dense stellar clusters have always drawn attention due to their potential in a number of phenomena, especially the dynamical formation of binary black holes (bbh), which potentially coalesce via gravitational-wave radiation. this study presents a preliminary set of evolutionary models of compact stellar clusters with initial masses ranging over 1.0 × 104-5.0 × 104 m⊙, and half-mass radius of 2 or 1 pc, which is typical for young massive and starburst clusters. they have metallicities between 0.05 z⊙ and z⊙. including contemporary schemes for stellar wind and remnant formation, such model clusters are evolved, for the first time, using the state-of-the-art direct n-body evolution program nbody7, until their dissolution or at least for 10 gyr. that way, a self-regulatory behaviour in the effects of dynamical interactions among the bhs is demonstrated. in contrast to earlier studies, the bbh coalescences obtained in these models show a prominence in triple-mediated coalescences while being bound to the clusters, compared to those occurring among the bbhs that are dynamically ejected from the clusters. a broader mass spectrum of the bhs and lower escape velocities of the clusters explored here might cause this difference, which is yet to be fully understood. among the bbh coalescences obtained here, there are ones that resemble the detected gw151226, lvt151012 and gw150914 events and also ones that are even more massive. a preliminary estimate suggests few 10-100 s of bbh coalescences per year, originating due to dynamics in stellar clusters that can be detected by the laser interferometer gravitational-wave observatory (ligo) at its design sensitivity. | stellar-mass black holes in young massive and open stellar clusters and their role in gravitational-wave generation |
we report on a search for compact binary coalescences where at least one binary component has a mass between 0.2 m⊙ and 1.0 m⊙ in advanced ligo and advanced virgo data collected between 1 april 2019 1500 utc and 1 october 2019 1500 utc. we extend our previous analyses in two main ways: we include data from the virgo detector and we allow for more unequal mass systems, with mass ratio q ≥0.1 . we do not report any gravitational-wave candidates. the most significant trigger has a false alarm rate of 0.14 yr-1. this implies an upper limit on the merger rate of subsolar binaries in the range [220 −24200 ] gpc-3 yr-1 , depending on the chirp mass of the binary. we use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. one is an isotropic distribution of equal-mass primordial black holes. using this model, we find that the fraction of dark matter in primordial black holes in the mass range 0.2 m⊙<mpbh<1.0 m⊙ is fpbh≡ωpbh/ωdm ≲6 % . this improves existing constraints on primordial black hole abundance by a factor of ∼3 . the other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. the upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at mmin=1 m⊙ , where fdbh≡ωdbh/ωdm ≲0.003 % . these are the first constraints placed on dissipative dark models by subsolar-mass analyses. | search for subsolar-mass binaries in the first half of advanced ligo's and advanced virgo's third observing run |
anisotropic stresses are ubiquitous in nature, but their modeling in general relativity is poorly understood and frame dependent. we introduce the first study on the dynamical properties of anisotropic self-gravitating fluids in a covariant framework. our description is particularly useful in the context of tests of the black hole paradigm, wherein ultracompact objects are used as black hole mimickers but otherwise lack a proper theoretical framework. we show the following: (i) anisotropic stars can be as compact and as massive as black holes, even for very small anisotropy parameters; (ii) the nonlinear dynamics of the 1 +1 system is in good agreement with linearized calculations, and shows that configurations below the maximum mass are nonlinearly stable; (iii) strongly anisotropic stars have vanishing tidal love numbers in the black-hole limit; and (iv) their formation will usually be accompanied by gravitational-wave echoes at late times. | anisotropic stars as ultracompact objects in general relativity |
while the equation of state (eos) of symmetric nuclear matter (snm) at suprasaturation densities has been relatively well constrained from heavy-ion collisions, the eos of high-density neutron-rich matter is still largely uncertain due to the poorly known high-density behavior of the symmetry energy. using the constraints on the eos of snm at suprasaturation densities from heavy-ion collisions together with the data of finite nuclei and the existence of 2 m⊙ neutron stars from electromagnetic observations, we show that the high-density symmetry energy cannot be too soft, which leads to lower bounds on dimensionless tidal deformability of λ1.4≥193 and radius of r1.4≥11.1 km for 1.4 m⊙ neutron star. furthermore, we find that the recent constraint of λ1.4≤580 from the gravitational wave signal gw170817 detected from the binary neutron star merger by the ligo and virgo collaborations rules out too-stiff high-density symmetry energy, leading to an upper limit of r1.4≤13.3 km . all these terrestrial nuclear experiments and astrophysical observations based on strong, electromagnetic, and gravitational measurements together put stringent constraints on the high-density symmetry energy and the eos of snm, pure neutron matter, and neutron star matter. | equation of state of dense matter in the multimessenger era |
we demonstrate the flexibility and utility of the berger-rigoutsos adaptive mesh refinement (amr) algorithm used in the open-source numerical relativity (nr) code grchombo for generating gravitational waveforms from binary black-hole (bh) inspirals, and for studying other problems involving non-trivial matter configurations. we show that grchombo can produce high quality binary bh waveforms through a code comparison with the established nr code lean. we also discuss some of the technical challenges involved in making use of full amr (as opposed to, e.g. moving box mesh refinement), including the numerical effects caused by using various refinement criteria when regridding. we suggest several 'rules of thumb' for when to use different tagging criteria for simulating a variety of physical phenomena. we demonstrate the use of these different criteria through example evolutions of a scalar field theory. finally, we also review the current status and general capabilities of grchombo. | lessons for adaptive mesh refinement in numerical relativity |
the measurement of the expansion history of the universe from the redshift unknown gravitational wave (gw) sources (dark gw sources) detectable from the network of ligo-virgo-kagra (lvk) detectors depends on the synergy with the galaxy surveys having accurate redshift measurements over a broad redshift range, large sky coverage, and detectability of fainter galaxies.in this work, we explore the possible synergy of the lvk with the spectroscopic galaxy surveys, such as desi and spherex, to measure the cosmological parameters which are related to the cosmic expansion history and the gw bias parameters. we show that by using the 3d spatial cross-correlation between the dark gw sources and the spectroscopic galaxy samples, we can measure the value of hubble constant with about $2{{\ \rm per\ cent}}$ and $1.5{{\ \rm per\ cent}}$ precision from lvk+desi and lvk+spherex, respectively within the 5 yr of observation time with $50{{\ \rm per\ cent}}$ duty-cycle. similarly, the dark energy equation of state can be measured with about $10{{\ \rm per\ cent}}$ and $8{{\ \rm per\ cent}}$ precision from lvk+desi and lvk+spherex, respectively. we find that due to the large sky coverage of spherex than desi, performance in constraining the cosmological parameters is better from the former than the latter. by combining euclid along with desi and spherex, a marginal gain in the measurability of the cosmological parameters is possible from the sources at high redshift (z ≥ 0.9). | mapping the cosmic expansion history from ligo-virgo-kagra in synergy with desi and spherex |
we perform a new test of general relativity (gr) with signals from gwtc-2, the ligo and virgo catalog of gravitational wave detections. we search for the presence of amplitude birefringence, in which left versus right circularly polarized modes of gravitational waves are exponentially enhanced and suppressed during propagation. such an effect is present in various beyond-gr theories but is absent in gr. we constrain the amount of amplitude birefringence consistent with the data through an opacity parameter κ , which we bound to be κ ≲0.74 gpc-1. our constraint is derived under an assumption that all gwtc-2 events have a common distance. this result for κ is statistically significant, with a jensen-shannon divergence of 7 ×10-2 bits compared to an uninformative distribution on κ . we then use these theory-agnostic results to constrain chern-simons gravity, a beyond-gr theory with motivations in quantum gravity. we bound the canonical chern-simons lengthscale to be ℓ0≲1.0 ×103 km , in agreement with other long-distance measurement results. | constraining gravitational wave amplitude birefringence and chern-simons gravity with gwtc-2 |
we perform a complementarity study of gravitational waves and colliders in the context of electroweak phase transitions choosing as our template the xsm model, which consists of the standard model augmented by a real scalar. we carefully analyze the gravitational wave signal at benchmark points compatible with a first order phase transition, taking into account subtle issues pertaining to the bubble wall velocity and the hydrodynamics of the plasma. in particular, we comment on the tension between requiring bubble wall velocities small enough to produce a net baryon number through the sphaleron process, and large enough to obtain appreciable gravitational wave production. for the most promising benchmark models, we study resonant di-higgs production at the high-luminosity lhc using machine learning tools: a gaussian process algorithm to jointly search for optimum cut thresholds and tuning hyperparameters, and a boosted decision trees algorithm to discriminate signal and background. the multivariate analysis on the collider side is able either to discover or provide strong statistical evidence of the benchmark points, opening the possibility for complementary searches for electroweak phase transitions in collider and gravitational wave experiments. | resonant di-higgs production at gravitational wave benchmarks: a collider study using machine learning |
there are at least two formation scenarios consistent with the first gravitational-wave observations of binary black hole mergers. in field models, black hole binaries are formed from stellar binaries that may undergo common envelope evolution. in dynamic models, black hole binaries are formed through capture events in globular clusters. both classes of models are subject to significant theoretical uncertainties. nonetheless, the conventional wisdom holds that the distribution of spin orientations of dynamically merging black holes is nearly isotropic while field-model black holes prefer to spin in alignment with the orbital angular momentum. we present a framework in which observations of black hole mergers can be used to measure ensemble properties of black hole spin such as the typical black hole spin misalignment. we show how to obtain constraints on population hyperparameters using minimal assumptions so that the results are not strongly dependent on the uncertain physics of formation models. these data-driven constraints will facilitate tests of theoretical models and help determine the formation history of binary black holes using information encoded in their observed spins. we demonstrate that the ensemble properties of binary detections can be used to search for and characterize the properties of two distinct populations of black hole mergers. | determining the population properties of spinning black holes |
we provide the first comprehensive study of hyperons in neutron star mergers and quantify their specific impact. we discuss the thermal behavior of hyperonic equations of state~(eoss) as a distinguishing feature from purely nucleonic models in the remnants of binary mergers using a large set of numerical simulations. finite temperature enhances the production of hyperons, which leads to a reduced pressure as highly degenerate nucleons are depopulated. this results in a characteristic increase of the dominant postmerger gravitational-wave frequency by up to $\sim150$~hz compared to purely nucleonic eos models. by our comparative approach we can directly link this effect to the occurrence of hyperons. although this feature is generally weak, it is in principle measurable if the eos and stellar parameters of cold neutron stars are sufficiently well determined. considering that the mass-radius relations of purely nucleonic and hyperonic eoss may be indistinguishable and the overall challenge to infer the presence of hyperons in neutron stars, these findings are important as a new route to answer the outstanding question about hyperonic degrees of freedom in high-density matter. | thermal behavior as indicator for hyperons in binary neutron star merger remnants |
using high-resolution hydrodynamics simulations, we show that equal-mass binaries accreting from a circumbinary disk evolve toward an orbital eccentricity of e ≃ 0.45, unless they are initialized on a nearly circular orbit with e ≲ 0.08, in which case they further circularize. the implied bi-modal eccentricity distribution resembles that seen in post-agb stellar binaries. large accretion spikes around periapse impart a tell-tale, quasiperiodic, bursty signature on the light curves of eccentric binaries. we predict that intermediate-mass and massive black hole binaries at z ≲ 10 entering the lisa band will have measurable eccentricities in the range of e ≃ 10-3 - 10-2, if they have experienced a gas-driven phase. on the other hand, gw190521 would have entered the ligo/virgo band with undetectable eccentricity ∼10-6 if it had been driven into the gravitational-wave regime by a gas disk. | equilibrium eccentricity of accreting binaries |
we develop a systematic framework to compute the conformal partial wave expansions (cpwes) of tree-level four-point witten diagrams with totally symmetric external fields of arbitrary mass and integer spin in ads d+1. as an intermediate step, we identify convenient bases of three-point bulk and boundary structures to invert linear map between spinning three-point conformal structures and spinning cubic couplings in ads. given a cft d , this provides the complete holographic reconstruction of all cubic couplings involving totally symmetric fields in the putative dual theory on ads d+1. employing this framework, we determine the cpwe of a generic four-point exchange witten diagram with spinning exchanged field. as a concrete application, we compute all four-point exchange witten diagrams in the type a higher-spin gauge theory on ads d+1, which is conjectured to be dual to the free scalar o ( n ) model. | spinning witten diagrams |
in this paper, we explore the prospect for improving the measurement accuracy of masses and radii of neutron stars. we consider imminent and long-term upgrades of the laser interferometer gravitational-wave observatory (ligo) and virgo, as well as next-generation observatories -- the cosmic explorer and einstein telescope. we find that neutron star radius with single events will be constrained to within roughly 500m with the current generation of detectors and their upgrades. this will improve to 200m, 100m and 50m with a network of observatories that contain one, two or three next-generation observatories, respectively. combining events in bins of 0.05 solar masses we find that for stiffer (softer) equations-of-state like alf2 (apr4), a network of three xg observatories will determine the radius to within 30m (100m) over the entire mass range of neutron stars from 1 to 2.0 solar masses (2.2 solar masses), allowed by the respective equations-of-state. neutron star masses will be measured to within 0.5 percent with three xg observatories irrespective of the actual equation-of-state. measurement accuracies will be a factor of 4 or 2 worse if the network contains only one or two xg observatories, respectively, and a factor of 10 worse in the case of networks consisting of advanced ligo, virgo kagra and their upgrades. tens to hundreds of high-fidelity events detected by future observatories will allow us to accurately measure the mass-radius curve and hence determine the dense matter equation-of-state to exquisite precision. | the accuracy of neutron star radius measurement with the next generation of terrestrial gravitational-wave observatories |
the recent direct observation of gravitational wave event gw170817 and its {grb}170817{a} grb 170817 a signal has opened up a new window to studying neutron stars and heralds a new era of astronomy referred to as the multimessenger astronomy. both gravitational and electromagnetic waves from a single astrophysical source have been detected for the first time. this combined detection offers an unprecedented opportunity to place constraints on the neutron star matter equation of state (eos). the existence of a possible hadron-quark phase transition in the central regions of neutron stars is associated with the appearance of g modes, which are extremely important as they could signal the presence of a pure quark matter core in the centers of neutron stars. observations of g modes with frequencies between 1 and 1.5 khz could be interpreted as evidence of a sharp hadron-quark phase transition in the cores of neutron stars. in this article, we shall review the description of the dense matter composing neutron stars, the determination of the eos of such matter, and the constraints imposed by astrophysical observations of these fascinating compact objects. | phase transitions in neutron stars and their links to gravitational waves |
gravitational-wave astrophysics has the potential to be transformed by a global network of longer, colder, and thus more sensitive detectors. this network must be constructed to address a wide range of science goals, involving binary coalescence signals as well as signals from other, potentially unknown, sources. it is crucial to understand which network configurations—the number, type, and location of the detectors in the network—can best achieve these goals. in this work we examine a large number of possible three-detector networks, variously composed of voyager, einstein telescope, and cosmic explorer detectors, and evaluate their performance against a number of figures of merit meant to capture a variety of future science goals. from this we infer that network performance, including sky localization, is determined most strongly by the type of detectors contained in the network, rather than the location and orientation of the facilities. | metrics for next-generation gravitational-wave detectors |
the mass-type quadrupole moment of inspiralling compact binaries (without spins) is computed at the fourth post-newtonian (4pn) approximation of general relativity. the multipole moments are defined by matching between the field in the exterior zone of the matter system and the pn field in the near zone, following the multipolar-post-minkowskian (mpm)-pn formalism. the matching implies a specific regularization for handling infra-red (ir) divergences of the multipole moments at infinity, based on the hadamard finite part procedure. on the other hand, the calculation entails ultra-violet (uv) divergences due to the modelling of compact objects by delta-functions, that are treated with dimensional regularization (dr). in future work we intend to systematically study the ir divergences by means of dimensional regularization as well. our result constitutes an important step in the goal of obtaining the gravitational wave templates of inspiralling compact binary systems with 4pn/4.5pn accuracy. | the mass quadrupole moment of compact binary systems at the fourth post-newtonian order |
we consider an extension of the standard model that accounts for the muon g - 2 tension and neutrino masses and study in detail dark matter phenomenology. the model under consideration includes a wimp and a fimp scalar dark matter candidates and thus gives rise to two-component dark matter scenarios. we discuss different regimes and mechanisms of production, including the novel freeze-in semi-production, and show that the wimp and fimp together compose the observed relic density today. the presence of the extra scalar fields allows phase transitions of the first order. we examine the evolution of the vacuum state and discuss stochastic gravitational wave signals associated with the first-order phase transition. we show that the gravitational wave signals may be probed by future gravitational wave experiments which may serve as a complementary detection signal. | a two-component dark matter model and its associated gravitational waves |
we develop a numerical approach to find asymptotically flat black hole solutions coupled to anisotropic fluids, described by generic density profiles. our model allows for a variety of applications in realistic astrophysical scenarios, and is potentially able to describe the geometry of galaxies hosting supermassive black holes, dark matter environments, and accretion phenomena. we apply our framework to a black hole surrounded by different families of dark matter profiles, namely the hernquist, the navarro-frenk white, and the einasto models. we study the geodesic motion of light and of massive particles in such spacetimes. moreover we compute gravitational axial perturbations induced by a small secondary on the numerical background and determine the changes in the emitted gravitational wave fluxes compared to the vacuum case. our analysis confirms and extends previous studies showing that modifications of orbital frequencies and axial fluxes can be described in terms of gravitational redshift, regardless of the halo model. | black holes surrounded by generic dark matter profiles: appearance and gravitational-wave emission |
gravitational wave data from ground-based detectors is dominated by instrument noise. signals will be comparatively weak, and our understanding of the noise will influence detection confidence and signal characterization. mismodeled noise can produce large systematic biases in both model selection and parameter estimation. here we introduce a multicomponent, variable dimension, parametrized model to describe the gaussian-noise power spectrum for data from ground-based gravitational wave interferometers. called bayesline, the algorithm models the noise power spectral density using cubic splines for smoothly varying broadband noise and lorentzians for narrow-band line features in the spectrum. we describe the algorithm and demonstrate its performance on data from the fifth and sixth ligo science runs. once fully integrated into ligo/virgo data analysis software, bayesline will produce accurate spectral estimation and provide a means for marginalizing inferences drawn from the data over all plausible noise spectra. | bayesian inference for spectral estimation of gravitational wave detector noise |
eccentricity and spin precession are key observables in gravitational-wave astronomy, encoding precious information about the astrophysical formation of compact binaries together with fine details of the relativistic two-body problem. however, the two effects can mimic each other in the emitted signals, raising issues around their distinguishability. since inferring the existence of both eccentricity and spin precession simultaneously is - at present - not possible, current state-of-the-art analyses assume that either one of the effects may be present in the data. in such a setup, what are the conditions required for a confident identification of either effect? we present simulated parameter inference studies in realistic ligo/virgo noise, studying events consistent with either spin precessing or eccentric binary black hole coalescences and recovering under the assumption that either of the two effects may be at play. we quantify how the distinguishability of eccentricity and spin precession increases with the number of visible orbital cycles, confirming that the signal must be sufficiently long for the two effects to be separable. the threshold depends on the injected source, with inclination, eccentricity, and effective spin playing crucial roles. in particular, for injections similar to gw190521, we find that it is impossible to confidently distinguish eccentricity from spin precession. | eccentricity or spin precession? distinguishing subdominant effects in gravitational-wave data |
the bubble wall velocity is essential for the phase transition dynamics in the early universe and its cosmological implications, such as the energy budget of phase transition gravitational wave and electroweak baryogenesis. one key factor to determine the wall velocity is the collision term that quantifies the interactions between the massive particles in the plasma and the bubble wall. we improve the calculations of the collision term beyond the leading-log approximation, and further obtain more precise bubble wall velocity for a representative effective model. | bubble wall velocity beyond leading-log approximation in electroweak phase transition |
spin precession is a generic feature of compact binary coalescences that leaves clear imprints in the gravitational waveforms. building on previous work, we present an efficient time domain inspiral-merger-ringdown effective-one-body model for precessing binary black holes, which incorporates subdominant modes beyond ℓ=2 , and the first effective-one-body frequency domain approximant for precessing binary neutron stars. we validate our model against 99 "short" numerical relativity precessing waveforms, where we find median mismatches of 5 ×10-3, 7 ×10-3 at inclinations of 0, π /3 , and 21 "long" waveforms with median mismatches of 4 ×10-3 and 5 ×10-3 at the same inclinations. further comparisons against the state-of-the-art nrsur7dq4 waveform model yield median mismatches of 4 ×10-3 , 1.8 ×10-2 at inclinations of 0 ,π /3 for 5000 precessing configurations with the precession parameter χp up to 0.8 and mass ratios up to 4. to demonstrate the computational efficiency of our model we apply it to parameter estimation and reanalyze the gravitational-wave events gw150914, gw190412, and gw170817. | effective-one-body waveforms for precessing coalescing compact binaries with post-newtonian twist |
we establish a correspondence between perturbative classical gluon and gravitational radiation emitted by spinning sources, to linear order in spin. this is an extension of the nonspinning classical perturbative double copy and uses the same color-to-kinematic replacements. the gravitational theory has a scalar (dilaton) and a 2-form field (the kalb-ramond axion) in addition to the graviton. in a preceding paper [w. d. goldberger et al., phys. rev. d 97, 105018 (2018), 10.1103/physrevd.97.105018], we computed axion radiation in the gravitational theory to show that the correspondence fixes its action. here, we present complete details of the gravitational computation. in particular, we also calculate the graviton and dilaton amplitudes in this theory and find that they precisely match with the predictions of the double copy. this constitutes a nontrivial check of the classical double copy correspondence and brings us closer to the goal of simplifying the calculation of gravitational wave observables for astrophysically relevant sources. | gravitational radiation from the classical spinning double copy |
we present a family of exact black-hole solutions on a static spherically symmetric background in second-order generalized proca theories with derivative vector-field interactions coupled to gravity. we also derive nonexact solutions in power-law coupling models including vector galileons and numerically show the existence of regular black holes with a primary hair associated with the longitudinal propagation. the intrinsic vector-field derivative interactions generally give rise to a secondary hair induced by nontrivial field profiles. the deviation from general relativity is most significant around the horizon and hence there is a golden opportunity for probing the proca hair by the measurements of gravitational waves (gws) in the regime of strong gravity. | hairy black-hole solutions in generalized proca theories |
in this letter, we propose that a fast radio burst (frb) could originate from the magnetic interaction between double neutron stars (nss) during their final inspiral within the framework of a unipolar inductor model. in this model, an electromotive force is induced on one ns to accelerate electrons to an ultra-relativistic speed instantaneously. we show that coherent curvature radiation from these electrons moving along magnetic field lines in the magnetosphere of the other ns is responsible for the observed frb signal, that is, the characteristic emission frequency, luminosity, duration, and event rate of frbs can be well understood. in addition, we discuss several implications of this model, including double-peaked frbs and possible associations of frbs with short-duration gamma-ray bursts and gravitational-wave events. | fast radio bursts from the inspiral of double neutron stars |
we study gravitational wave production from gauge preheating in a variety of inflationary models, detailing its dependence on both the energy scale and the shape of the potential. we show that preheating into abelian gauge fields generically leads to a large gravitational wave background that contributes significantly to the effective number of relativistic degrees of freedom in the early universe, neff . we demonstrate that the efficiency of gravitational wave production is correlated with the tensor-to-scalar ratio, r . in particular, we show that efficient gauge preheating in models whose tensor-to-scalar ratio would be detected by next-generation cosmic microwave background experiments (r ≳1 0-3 ) will be either detected through its contribution to neff or ruled out. furthermore, we show that bounds on neff provide the most sensitive probe of the possible axial coupling of the inflaton to gauge fields regardless of the potential. | constraining axion inflation with gravitational waves from preheating |
it is known that a near-extremal kerr black hole can be spun up beyond its extremal limit by capturing a test particle. here we show that overspinning is always averted once backreaction from the particle's own gravity is properly taken into account. we focus on nonspinning, uncharged, massive particles thrown in along the equatorial plane and work in the first-order self-force approximation (i.e., we include all relevant corrections to the particle's acceleration through linear order in the ratio, assumed small, between the particle's energy and the black hole's mass). our calculation is a numerical implementation of a recent analysis by two of us [phys. rev. d 91, 104024 (2015)], in which a necessary and sufficient "censorship" condition was formulated for the capture scenario, involving certain self-force quantities calculated on the one-parameter family of unstable circular geodesics in the extremal limit. the self-force information accounts both for radiative losses and for the finite-mass correction to the critical value of the impact parameter. here we obtain the required self-force data and present strong evidence to suggest that captured particles never drive the black hole beyond its extremal limit. we show, however, that, within our first-order self-force approximation, it is possible to reach the extremal limit with a suitable choice of initial orbital parameters. to rule out such a possibility would require (currently unavailable) information about higher-order self-force corrections. | self-force as a cosmic censor in the kerr overspinning problem |
merging binary neutron stars (bnss) represent the ultimate targets for multimessenger astronomy, being among the most promising sources of gravitational waves (gws), and, at the same time, likely accompanied by a variety of electromagnetic counterparts across the entire spectrum, possibly including short gamma-ray bursts (sgrbs) and kilonova/macronova transients. numerical relativity simulations play a central role in the study of these events. in particular, given the importance of magnetic fields, various aspects of this investigation require general relativistic magnetohydrodynamics (grmhd). so far, most grmhd simulations focused the attention on bns mergers leading to the formation of a hypermassive neutron star (ns), which, in turn, collapses within few tens of ms into a black hole surrounded by an accretion disk. however, recent observations suggest that a significant fraction of these systems could form a long-lived ns remnant, which will either collapse on much longer time scales or remain indefinitely stable. despite the profound implications for the evolution and the emission properties of the system, a detailed investigation of this alternative evolution channel is still missing. here, we follow this direction and present a first detailed grmhd study of bns mergers forming a long-lived ns. we consider magnetized binaries with different mass ratios and equations of state and analyze the structure of the ns remnants, the rotation profiles, the accretion disks, the evolution and amplification of magnetic fields, and the ejection of matter. moreover, we discuss the connection with the central engine of sgrbs and provide order-of-magnitude estimates for the kilonova/macronova signal. finally, we study the gw emission, with particular attention to the post-merger phase. | general relativistic magnetohydrodynamic simulations of binary neutron star mergers forming a long-lived neutron star |
we study gauge (in)dependence of the gravitational waves (gws) induced from curvature perturbations. for the gws produced in a radiation-dominated era, we find that the observable (late-time) gws in the transverse-traceless (synchronous) gauge and in the newtonian gauge are the same in contrast to a claim in the literature. we also mention the interpretation of the gauge dependence of the tensor perturbations which appears in the context of the induced gws. | gauge independence of induced gravitational waves |
we study the scalar triplet extension of the standard model with a low cutoff, preventing large corrections to the quadratic masses that would otherwise worsen the hierarchy problem. we explore the reach of lisa to test the parameter space region of the scalar potential (not yet excluded by higgs to diphoton measurements) in which the electroweak phase transition is strongly first-order and produces sizeable gravitational waves. we also demonstrate that the collider phenomenology of the model is drastically different from its renormalizable counterpart. we study the reach of the lhc in ongoing searches and project bounds for the hl-lhc. likewise, we develop a dedicated analysis to test the key but still unexplored signature of pair-production of charged scalars decaying to third-generation quarks: pp→ t\overline{b} (\overline{t}b), b\overline{b}. these results apply straightforwardly to other extensions of the higgs sector such as the 2hdm/mssm. | gravitational wave and collider probes of a triplet higgs sector with a low cutoff |
the primordial irreducible gravitational-wave background due to quantum vacuum tensor fluctuations produced during inflation spans a large range of frequencies with an almost scale-invariant spectrum but is too low to be detected by the next generation of gravitational-wave interferometers. we show how this signal is enhanced by a short temporary kination era in the cosmological history (less than 10 e-folds), that can arise at any energy scale between a gev and the inflationary scale $10^{16}$ gev. we argue that such kination era is naturally generated by a spinning axion before it gets trapped by its potential. it is usually assumed that the axion starts oscillating around its minimum from its initially frozen position. however, the early dynamics of the peccei-quinn field can induce a large kinetic energy in the axion field, triggering a kination era, either before or after the axion acquires its mass, leading to a characteristic peak in the primordial gravitational-wave background. this represents a smoking-gun signature of axion physics as no other scalar field dynamics is expected to trigger such a sequence of equations of state in the early universe. we derive the resulting gravitational-wave spectrum, and present the parameter space that leads to such a signal as well as the detectability prospects, in particular at lisa, einstein telescope, cosmic explorer and big bang observer. we show both model-independent predictions and present as well results for two specific well-motivated uv completions for the qcd axion dark matter where this dynamics is built-in. | revealing the primordial irreducible inflationary gravitational-wave background with a spinning peccei-quinn axion |
scattering amplitudes are both a wonderful playground to discover novel ideas in quantum field theory and simultaneously of immense phenomenological importance to make precision predictions for e.g. particle collider observables and more recently also for gravitational wave signals. in this review chapter, we give an overview of some of the exciting recent progress on reformulating qft in terms of mathematical, geometric quantities, such as polytopes, associahedra, grassmanians, and the amplituhedron. in this novel approach, standard notions of locality and unitarity are derived concepts rather than fundamental ingredients in the construction which might give us a handle on a number of open questions in qft that have evaded an answer for decades. we first give a basic summary of positive geometry before discussing the associahedron-one of the simplest physically relevant geometric examples-and its relation to tree-level scattering amplitudes in bi-adjoint ϕ 3 theory. our second example is the amplituhedron construction for scattering amplitudes in planar maximally supersymmetric yang-mills theory. | the sagex review on scattering amplitudes chapter 7: positive geometry of scattering amplitudes |
surface gravity waves generated by winds are ubiquitous on our oceans and play a primordial role in the dynamics of the ocean-land-atmosphere interfaces. in particular, wind-generated waves cause fluctuations of the sea level at the coast over timescales from a few seconds (individual wave runup) to a few hours (wave-induced setup). these wave-induced processes are of major importance for coastal management as they add up to tides and atmospheric surges during storm events and enhance coastal flooding and erosion. changes in the atmospheric circulation associated with natural climate cycles or caused by increasing greenhouse gas emissions affect the wave conditions worldwide, which may drive significant changes in the wave-induced coastal hydrodynamics. since sea-level rise represents a major challenge for sustainable coastal management, particularly in low-lying coastal areas and/or along densely urbanized coastlines, understanding the contribution of wind-generated waves to the long-term budget of coastal sea-level changes is therefore of major importance. in this review, we describe the physical processes by which sea states may affect coastal sea level at several timescales, we present the methods currently used to estimate the wave contribution to coastal sea-level changes, we describe past and future wave climate variability, we discuss the contribution of wave to coastal sea-level changes, and we discuss the limitations and perspectives of this research field. | the contribution of wind-generated waves to coastal sea-level changes |
we present and assess a bayesian method to interpret gravitational wave signals from binary black holes. our method directly compares gravitational wave data to numerical relativity (nr) simulations. in this study, we present a detailed investigation of the systematic and statistical parameter estimation errors of this method. this procedure bypasses approximations used in semianalytical models for compact binary coalescence. in this work, we use the full posterior parameter distribution for only generic nonprecessing binaries, drawing inferences away from the set of nr simulations used, via interpolation of a single scalar quantity (the marginalized log likelihood, ln l ) evaluated by comparing data to nonprecessing binary black hole simulations. we also compare the data to generic simulations, and discuss the effectiveness of this procedure for generic sources. we specifically assess the impact of higher order modes, repeating our interpretation with both l ≤2 as well as l ≤3 harmonic modes. using the l ≤3 higher modes, we gain more information from the signal and can better constrain the parameters of the gravitational wave signal. we assess and quantify several sources of systematic error that our procedure could introduce, including simulation resolution and duration; most are negligible. we show through examples that our method can recover the parameters for equal mass, zero spin, gw150914-like, and unequal mass, precessing spin sources. our study of this new parameter estimation method demonstrates that we can quantify and understand the systematic and statistical error. this method allows us to use higher order modes from numerical relativity simulations to better constrain the black hole binary parameters. | parameter estimation method that directly compares gravitational wave observations to numerical relativity |
ejected material from neutron star mergers gives rise to electromagnetic emission powered by radioactive decays of r-process nuclei, the so-called kilonova or macronova. while properties of the emission are largely affected by opacities in the ejected material, available atomic data for r-process elements are still limited. we perform atomic structure calculations for r-process elements: se (z = 34), ru (z = 44), te (z = 52), ba (z = 56), nd (z = 60), and er (z = 68). we confirm that the opacities from bound-bound transitions of open f-shell, lanthanide elements (nd and er) are higher than those of the other elements over a wide wavelength range. the opacities of open s-shell (ba), p-shell (se and te), and d-shell (ru) elements are lower than those of open f-shell elements, and their transitions are concentrated in the ultraviolet and optical wavelengths. we show that the optical brightness can be different by > 2 mag depending on the element abundances in the ejecta such that post-merger, lanthanide-free ejecta produce brighter and bluer optical emission. such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small. for the ejecta mass of 0.01 {m}⊙ , observed magnitudes of the blue emission will reach 21.0 mag (100 mpc) and 22.5 mag (200 mpc) in the g and r bands within a few days after the merger, which are detectable with 1 m or 2 m class telescopes. | properties of kilonovae from dynamical and post-merger ejecta of neutron star mergers |
in summer 2017 gravitational waves (gws) from a binary neutron star (ns) merger were detected for the first time. moreover, electromagnetic emission was observed and associated with the merger. this very first unambiguous observation of a ns coalescence has impressively advanced our understanding of the merger process and has set some first constraints on the macroscopic properties of nss, with direct implications for the high-density equation of state. we discuss work on ns mergers focusing on the postmerger gw emission. these studies are based on numerical simulations of the merger and survey a large sample of candidate equations of state for ns matter. the goal is to connect observables with the underlying physics questions. this offers a way to constrain the properties of high-density matter through the determination of ns radii, as inferred by an empirical relation connecting the dominant gw frequency peak in the postmerger phase to the radius of nonrotating nss of a certain mass. we clarify the physical origin of secondary peaks and discuss a spectral classification scheme, based on their relative strength. observational prospects for the dominant and the secondary peaks are also discussed. the threshold mass to black-hole collapse is connected by another empirical relation to the maximum mass and compactness of nonrotating nss, which can be derived semi-analytically. the observation of gw170817 then sets an absolute minimum radius for nss of typical masses, based only on a minimal number of assumptions. | spectral classification of gravitational-wave emission and equation of state constraints in binary neutron star mergers |
we perform bayesian analysis of gravitational-wave signals from nonspinning, intermediate-mass black-hole binaries (imbhbs) with observed total mass, mobs, from 50 m⊙ to 500 m⊙ and mass ratio 1-4 using advanced ligo and virgo detectors. we employ inspiral-merger-ringdown waveform models based on the effective-one-body formalism and include subleading modes of radiation beyond the leading (2,2) mode. the presence of subleading modes increases signal power for inclined binaries and allows for improved accuracy and precision in measurements of the masses as well as breaking of degeneracies in distance, orientation and polarization. for low total masses, mobs≲50 m⊙ , for which the inspiral signal dominates, the observed chirp mass mobs=mobsη3 /5 (η being the symmetric mass ratio) is better measured. in contrast, as increasing power comes from merger and ringdown, we find that the total mass mobs has better relative precision than mobs. indeed, at high mobs (≥300 m⊙ ), the signal resembles a burst and the measurement thus extracts the dominant frequency of the signal that depends on mobs. depending on the binary's inclination, at signal-to-noise ratio (snr) of 12, uncertainties in mobs can be as large as ∼20 - 25 % while uncertainties in mobs are ∼50 - 60 % in binaries with unequal masses (those numbers become ∼17 % vs. ∼22 % in more symmetric mass-ratio binaries). although large, those uncertainties in mobs will establish the existence of imbhs. we find that effective-one-body waveforms with subleading modes are essential to confirm a signal's presence in the data, with calculated bayesian evidences yielding a false alarm probability below 10-5 for snr ≳9 in gaussian noise. our results show that gravitational-wave observations can offer a unique tool to observe and understand the formation, evolution and demographics of imbhs, which are difficult to observe in the electromagnetic window. | missing link: bayesian detection and measurement of intermediate-mass black-hole binaries |
the almost simultaneous detection of gravitational waves and a short gamma-ray burst from a neutron star merger has put a tight constraint on the difference between the speed of gravity and light. in the four-dimensional scalar-tensor theory with second-order equations of motion, the horndeski theory, this translates into a significant reduction of the viable parameter space of the theory. recently, extensions of horndeski theory, which are free from ostrogradsky ghosts despite the presence of higher-order derivatives in the equations of motion, have been identified and classified exploiting the degeneracy criterium. in these new theories, the fifth force mediated by the scalar field must be suppressed in order to evade the stringent solar system constraints. we study the vainshtein mechanism in the most general degenerate higher-order scalar-tensor theory in which light and gravity propagate at the same speed. we find that the vainshtein mechanism generally works outside a matter source but it is broken inside matter, similarly to beyond horndeski theories. this leaves interesting possibilities to test these theories that are compatible with gravitational wave observations using astrophysical objects. | vainshtein mechanism after gw170817 |
an evolving japanese gravitational-wave (gw) mission in the decihertz band, b-decigo (decihertz laser interferometer gravitational wave observatory), will enable us to detect gw150914-like binary black holes, gw170817-like binary neutron stars, and intermediate-mass binary black holes out to cosmological distances. the b-decigo band slots in between the aligo-virgo-kagra-indigo (hectohertz) and lisa (millihertz) bands for broader bandwidth; the sources described emit gws for weeks to years across the multiple bands to accumulate high signal-to-noise ratios. this suggests the possibility that joint detection would greatly improve the parameter estimation of the binaries. we examine b-decigo's ability to measure binary parameters and assess to what extent multiband analysis could improve such measurement. using non-precessing post-newtonian waveforms with the fisher matrix approach, we find for systems like gw150914 and gw170817 that b-decigo can measure the mass ratio to within < 0.1%, the individual black-hole spins to within < 10%, and the coalescence time to within < 5 s about a week before alerting aligo and electromagnetic facilities. prior information from b-decigo for aligo can further reduce the uncertainty in the measurement of, e.g., certain neutron star tidally induced deformations by a factor of ∼6, and potentially determine the spin-induced neutron star quadrupole moment. joint lisa and b-decigo measurement will also be able to recover the masses and spins of intermediate-mass binary black holes at percent-level precision. however, there will be a large systematic bias in these results due to post-newtonian approximation of exact gw signals. | multiband gravitational-wave astronomy: observing binary inspirals with a decihertz detector, b-decigo |
superradiance can trigger the formation of an ultralight boson cloud around a spinning black hole. once formed, the boson cloud is expected to emit a nearly periodic, long-duration, gravitational-wave signal. for boson masses in the range (10-13- 10-11) ev , and stellar mass black holes, such signals are potentially detectable by gravitational-wave detectors, like advanced ligo and virgo. in this letter, we present full band upper limits for a generic all-sky search for periodic gravitational waves in ligo o2 data, and use them to derive—for the first time—direct constraints on the ultralight scalar boson field mass. | direct constraints on the ultralight boson mass from searches of continuous gravitational waves |
up to the third post-newtonian (3pn) order, we compute (i) the current-type quadrupole moment of (non-spinning) compact binary systems, as well as (ii) the corresponding gravitational-wave mode (2, 1) (constituting a 3.5pn correction in the waveform). moreover, at this occasion, (iii) we recompute and confirm the previous calculation of the mass-type octupole moment to 3pn order. the ultra-violet divergences due to the point-like nature of the source are treated by means of dimensional regularization. this entails generalizing the definition of the irreducible mass and current multipole moments of an isolated pn source in d spatial dimensions. in particular, we find that the current type moment has the symmetry of a particular mixed young tableau and that, in addition, there appears a third type of moment which is however inexistent in 3 spatial dimensions. | the current-type quadrupole moment and gravitational-wave mode (ℓ, m) = (2, 1) of compact binary systems at the third post-newtonian order |
among the known resources of quantum metrology, one of the most practical and efficient is squeezing. squeezed states of atoms and light improve the sensing of the phase, magnetic field, polarization, mechanical displacement. they promise to considerably increase signal-to-noise ratio in imaging and spectroscopy, and are already used in real-life gravitational-wave detectors. but despite being more robust than other states, they are still very fragile, which narrows the scope of their application. in particular, squeezed states are useless in measurements where the detection is inefficient or the noise is high. here, we experimentally demonstrate a remedy against loss and noise: strong noiseless amplification before detection. this way, we achieve loss-tolerant operation of an interferometer fed with squeezed and coherent light. with only 50% detection efficiency and with noise exceeding the level of squeezed light more than 50 times, we overcome the shot-noise limit by 6 db. sub-shot-noise phase sensitivity survives up to 87% loss. application of this technique to other types of optical sensing and imaging promises a full use of quantum resources in these fields. | overcoming detection loss and noise in squeezing-based optical sensing |
in the analysis of a binary black hole coalescence, it is necessary to include gravitational self-interactions in order to describe the transition of the gravitational wave signal from the merger to the ringdown stage. in this paper we study the phenomenology of the generation and propagation of nonlinearities in the ringdown of a schwarzschild black hole, using second-order perturbation theory. following earlier work, we show that the green's function and its causal structure determines how both first-order and second-order perturbations are generated, and hence highlight that both of these solutions share some physical properties. in particular, we discuss the sense in which both linear and quadratic quasinormal modes (qnms) are generated in the vicinity of the peak of the gravitational potential barrier (loosely referred to as the light ring). among the second-order perturbations, there are solutions with linear qnm frequencies (whose amplitudes are thus renormalized from their linear values), as well as quadratic qnm frequencies with a distinct spectrum. moreover, we show using a wentzel-kramers-brillouin analysis that, in the eikonal limit, waves generated inside the light ring propagate towards the black hole horizon, and only waves generated outside propagate towards an asymptotic observer. these results might be relevant for recent discussions on the validity of perturbation theory close to the merger. finally, we argue that even if nonlinearities are small, quadratic qnms may be detectable and would likely be useful for improving ringdown models of higher angular harmonics and future tests of gravity. | generation and propagation of nonlinear quasinormal modes of a schwarzschild black hole |
we investigate production of primordial black holes from first-order electroweak phase transition in the framework of the nearly aligned higgs effective field theory, in which non-decoupling quantum effects are properly described. since the mass of such primordial black holes is evaluated to be about 10-5 of the solar mass, current and future microlensing observations such as subaru hsc, ogle, prime and roman space telescope may be able to probe the electroweak phase transition. we study parameter regions where primordial black holes can be produced by the first-order electroweak phase transition, and explore their detectability at these observations. complementarity of primordial black hole observations, gravitational wave observations and collider experiments is also discussed for testing the nature of the electroweak phase transition. | probing first-order electroweak phase transition via primordial black holes in the effective field theory |
on the basis of s4max data retrieved from cosmic gps radio occultation measurements, the long-term climatology of the intensity of es layers is investigated for the period from december 2006 to january 2014. global maps of es intensity show the high-spatial-resolution geographical distribution and strong seasonal dependence of es layers. the maximum intensity of es occurs over the mid-latitudes, and its value in summer is 2-3 times larger than that in winter. a relatively strong es layer is observed at the north pole and south pole, with a distinct boundary dividing the mid-latitudes and high latitudes along the 60-80∘ geomagnetic latitude band. the simulation results show that the convergence of vertical ion velocity could partially explain the seasonal dependence of es intensity. furthermore, some disagreements between the distributions of the calculated divergence of vertical ion velocity and the observed es intensity indicate that other processes, such as the vertical motions of gravity waves, magnetic-field effects, meteoric mass influx into earth's atmosphere, and the chemical processes of metallic ions, should also be considered as they may also play an important role in the spatial and seasonal variations in es layers. | the global climatology of the intensity of the ionospheric sporadic e layer |
a model for wind-generated surface gravity waves, wavewatch iii®, is used to analyze and interpret buoy measurements of wave spectra. the model is applied to a hindcast of a wave event in sea ice in the western arctic, 11-14 october 2015, for which extensive buoy and ship-borne measurements were made during a research cruise. the model, which uses a viscoelastic parameterization to represent the impact of sea ice on the waves, is found to have good skill—after calibration of the effective viscosity—for prediction of total energy, but over-predicts dissipation of high frequency energy by the sea ice. this shortcoming motivates detailed analysis of the apparent dissipation rate. a new inversion method is applied to yield, for each buoy spectrum, the inferred dissipation rate as a function of wave frequency. for 102 of the measured wave spectra, visual observations of the sea ice were available from buoy-mounted cameras, and ice categories (primarily for varying forms of pancake and frazil ice) are assigned to each based on the photographs. when comparing the inversion-derived dissipation profiles against the independently derived ice categories, there is remarkable correspondence, with clear sorting of dissipation profiles into groups of similar ice type. these profiles are largely monotonic: they do not exhibit the "roll-over" that has been found at high frequencies in some previous observational studies. | dissipation of wind waves by pancake and frazil ice in the autumn beaufort sea |
we consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star-black hole mergers. these outflows, powered by angular momentum transport processes and nuclear recombination, represent an important - and in some cases dominant - contribution to the total mass ejected by the merger. here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. we find that outflows produce a robust abundance pattern around the second r-process peak (mass number a ∼ 130), independent of model parameters, with significant production of a < 130 nuclei. this implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of r-process elements in metal poor stars. disc outflows reach the third peak (a ∼ 195) in most of our simulations, although the amounts produced depend sensitively on the disc viscosity, initial mass or entropy of the torus, and nuclear physics inputs. some of our models produce an abundance spike at a = 132 that is absent in the solar system r-process distribution. the spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. we conclude that disc outflows provide an important - and perhaps dominant - contribution to the r-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of r-process elements in the galaxy. | production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers |
the nature of electroweak (ew) phase transition (pt) is of great importance. it may give a clue to the origin of baryon asymmetry if ewpt is strong first order. although it is a cross over within the standard model (sm), a great many extensions of the sm are capable of altering the nature. thus, gravitational wave (gw), which is supposed to be relics of strong first order pt, is a good complementary probe to new physics beyond sm (bsm). we in this paper elaborate the patterns of strong first order ewpt in the next to simplest extension to the sm higgs sector, by introducing a z 3-symmetric singlet scalar. we find that, in the z 3-symmetric limit, the tree level barrier could lead to strong first order ewpt either via three or two-step pt. moreover, they could produce two sources of gw, despite of the undetectability from the first-step strong first order pt for the near future gw experiments. but the other source with significant supercooling which then gives rise to α ∼ o(0.1) almost can be wholly covered by future space-based gw interferometers such as elisa, decigo and bbo. | strong first order ewpt & strong gravitational waves in z 3-symmetric singlet scalar extension |
the elastic properties of neutron star crusts are relevant for a variety of currently observable or near-future electromagnetic and gravitational wave phenomena. these phenomena may depend on the elastic properties of nuclear pasta found in the inner crust. we present large-scale classical molecular dynamics simulations where we deform nuclear pasta. we simulate idealized samples of nuclear pasta and describe their breaking mechanism. we also deform nuclear pasta that is arranged into many domains, similar to what is known for the ions in neutron star crusts. our results show that nuclear pasta may be the strongest known material, perhaps with a shear modulus of 1 030 ergs/cm 3 and a breaking strain greater than 0.1. | elasticity of nuclear pasta |
recent detections of merging black holes allow observational tests of the nature of these objects. in some proposed models, nontrivial structure at or near the black hole horizon could lead to echo signals in gravitational wave data. recently, abedi-dykaar-afshordi (ada) claimed tentative evidence for repeating damped echo signals following the gravitational-wave signals of the binary black hole merger events recorded in the first observational period of the advanced ligo interferometers. we reanalyze the same data, addressing some of the shortcomings of their method using more background data and a modified procedure. we find a reduced statistical significance for the claims of evidence for echoes, calculating increased p-values for the null hypothesis of echo-free noise. the reduced significance is entirely consistent with noise, and so we conclude that the analysis of abedi et al. does not provide any observational evidence for the existence of planck-scale structure at black hole horizons. | low significance of evidence for black hole echoes in gravitational wave data |
blip glitches are short noise transients present in data from ground-based gravitational-wave observatories. these glitches resemble the gravitational-wave signature of massive binary black hole mergers. hence, the sensitivity of transient gravitational-wave searches to such high-mass systems and other potential short duration sources is degraded by the presence of blip glitches. the origin and rate of occurrence of this type of glitch have been largely unknown. in this paper we explore the population of blip glitches in advanced ligo during its first and second observing runs. on average, we find that advanced ligo data contains approximately two blip glitches per hour of data. we identify four subsets of blip glitches correlated with detector auxiliary or environmental sensor channels, however the physical causes of the majority of blips remain unclear. | blip glitches in advanced ligo data |
data from the laser interferometer gravitational wave observatory (ligo) and virgo detectors have confirmed that stellar-mass black holes can merge within a hubble time, leaving behind massive remnant black holes. in some astrophysical environments such as globular clusters and active galactic nucleus disks, it may be possible for these remnants to take part in further compact-object mergers, producing a population of hierarchically formed black holes. in this work, we present a parameterized framework for describing the population of binary black hole (bbh) mergers, while self-consistently accounting for hierarchical mergers. the framework casts black holes as particles in a box that can collide based on an effective cross section, but allows inputs from more detailed astrophysical simulations. our approach is relevant to any population that is comprised of second- or higher-generation black holes, such as primordial black holes or dense cluster environments. we describe some possible inputs to this generic model and their effects on the black hole merger populations and use the model to perform bayesian inference on the catalog of black holes from ligo and virgo's first two observing runs. we find that models with a high rate of hierarchical mergers are disfavored, consistent with previous population analyses. future gravitational-wave events will further constrain the inputs to this generic hierarchical merger model, enabling a deeper look into the formation environments of bbhs. | black hole coagulation: modeling hierarchical mergers in black hole populations |
there is a guaranteed background of stochastic gravitational waves produced in the thermal plasma in the early universe. its energy density per logarithmic frequency interval scales with the maximum temperature tmax which the primordial plasma attained at the beginning of the standard hot big bang era. it peaks in the microwave range, at around 80 ghz [106.75/g*s(tmax)]1/3, where g*s(tmax) is the effective number of entropy degrees of freedom in the primordial plasma at tmax. we present a state-of-the-art prediction of this cosmic gravitational microwave background (cgmb) for general models, and carry out calculations for the case of the standard model (sm) as well as for several of its extensions. on the side of minimal extensions we consider the neutrino minimal sm (νmsm) and the sm-axion-seesaw-higgs portal inflation model (smash), which provide a complete and consistent cosmological history including inflation. as an example of a non-minimal extension of the sm we consider the minimal supersymmetric standard model (mssm). furthermore, we discuss the current upper limits and the prospects to detect the cgmb in laboratory experiments and thus measure the maximum temperature and the effective number of degrees of freedom at the beginning of the hot big bang. | gravitational waves as a big bang thermometer |
with the aim of providing high accuracy post-newtonian (pn) templates for the analysis of gravitational waves generated by compact binary systems, we complete the analytical derivation of the source type mass quadrupole moment of compact binaries (without spins) at the fourth pn order of general relativity. similarly to the case of the conservative 4pn equations of motion, we show that the quadrupole moment at that order contains a non-local (in time) contribution, arising from the tail-transported interaction entering the conservative part of the dynamics. furthermore, we investigate the infra-red (ir) divergences of the quadrupole moment. in a previous work, this moment has been computed using a hadamard partie finie procedure for the ir divergences, but the knowledge of the conservative equations of motion indicates that those divergences have to be dealt with by means of dimensional regularization. this work thus derives the difference between the two regularization schemes, which has to be added on top of the previous result. we show that unphysical ir poles start to appear at the 3pn order, and we determine all of these up to the 4pn order. in particular, the non-local tail term comes in along with a specific pole at the 4pn order. it will be proven in a companion paper that the poles in the source-type quadrupole are cancelled in the physical radiative type quadrupole moment measured at future null infinity. | the quadrupole moment of compact binaries to the fourth post-newtonian order: i. non-locality in time and infra-red divergencies |
the spin properties of merging black holes observed with gravitational waves can offer novel information about the origin of these systems. the magnitudes and orientations of black hole spins offer a record of binaries' evolutionary history, encoding information about massive stellar evolution and the astrophysical environments in which binary black holes are assembled. recent analyses of the binary black hole population have yielded conflicting portraits of the black hole spin distribution. some works suggest that black hole spins are small but nonzero and exhibit a wide range of misalignment angles relative to binaries' orbital angular momenta. other works conclude that the majority of black holes are nonspinning while the remainder are rapidly rotating and primarily aligned with their orbits. we revisit these conflicting conclusions, employing a variety of complementary methods to measure the distribution of spin magnitudes and orientations among binary black hole mergers. we find that the existence of a subpopulation of black holes with vanishing spins is not required by current data. should such a subpopulation exist, we conclude that it must contain ≲60% of binaries. additionally, we find evidence for significant spin-orbit misalignment among the binary black hole population, with some systems exhibiting misalignment angles greater than 90°, and see no evidence for an approximately spin-aligned subpopulation. | no evidence that the majority of black holes in binaries have zero spin |
we investigate a simple holographic model for cold and dense deconfined qcd matter consisting of three quark flavors. varying the single free parameter of the model and utilizing a chiral effective theory equation of state (eos) for nuclear matter, we find four different compact star solutions: traditional neutron stars, strange quark stars, as well as two non-standard solutions we refer to as hybrid stars of the second and third kind (hs2 and hs3). the hs2s are composed of a nuclear matter core and a crust made of stable strange quark matter, while the hs3s have both a quark mantle and a nuclear crust on top of a nuclear matter core. for all types of stars constructed, we determine not only their mass-radius relations, but also tidal deformabilities, love numbers, as well as moments of inertia and the mass distribution. we find that there exists a range of parameter values in our model, for which the novel hybrid stars have properties in very good agreement with all existing bounds on the stationary properties of compact stars. in particular, the tidal deformabilities of these solutions are smaller than those of ordinary neutron stars of the same mass, implying that they provide an excellent fit to the recent gravitational wave data gw170817 of ligo and virgo. the assumptions underlying the viability of the different star types, in particular those corresponding to absolutely stable quark matter, are finally discussed at some length. | holographic compact stars meet gravitational wave constraints |
black hole (bh) mergers driven by gravitational perturbations of external companions constitute an important class of formation channels for merging bh binaries detected by ligo. we have studied the orbital and spin evolution of binary bhs in triple systems, where the tertiary companion excites large eccentricity in the inner binary through lidov-kozai oscillations, causing the binary to merge via gravitational radiation. using the single-averaged and double-averaged secular dynamics of triples (where the equations of motion are averaged over the inner orbit and both orbits, respectively), we perform a large set of numerical integrations to determine the merger window (the range of companion inclinations that allows the inner binary to merge within ∼10 gyr) and the merger fraction as a function of various system parameters (e.g., the binary masses m 1, m 2 and initial semimajor axis a 0, the mass, semimajor axis, and eccentricity {e}out} of the outer companion). for typical bh binaries ({m}1,2}≃ 20 {m}⊙ {--}30 {m}⊙and a 0 ≳ 10 au), the merger fraction increases rapidly with e out because of the octupole perturbation, ranging from ∼1% at {e}out}=0 to 10%-20% at e out = 0.9. we derive analytical expressions and approximate scaling relations for the merger window and merger fraction for systems with negligible octupole effect, and apply them to neutron star binary mergers in triples. we also follow the spin evolution of the bhs during the companion-induced orbital decay, where de sitter spin precession competes with lidov-kozai orbital precession/nutation. starting from aligned spin axes (relative to the orbital angular momentum axis), a wide range of final spin-orbit misalignment angle θ sl f can be generated when the binary enters the ligo sensitivity band. for systems where the octupole effect is small (such as those with m 1 ≃ m 2 or e out ∼ 0), the distribution of {θ }sl}{{f}} peaks around 90°. as the octupole effect increases, a more isotropic distribution of final spin axis is produced. overall, merging bh binaries produced by lidov-kozai oscillations in triples exhibit a unique distribution of the effective (mass-weighted) spin parameter χ eff; this may be used to distinguish this formation channel from other dynamical channels. | black hole and neutron star binary mergers in triple systems: merger fraction and spin-orbit misalignment |
the treatment and criteria for development of unstable roche lobe overflow (rlof) that leads to the common envelope (ce) phase have hindered the area of evolutionary predictions for decades. in particular, the formation of black hole-black hole (bh-bh), black hole-neutron star (bh-ns), and neutron star-neutron star (ns-ns) merging binaries depends sensitively on the ce phase in classical isolated binary evolution model. all these mergers are now reported as ligo/virgo sources or source candidates. ce is even considered by some as a mandatory phase in the formation of bh-bh, bh-ns, or ns-ns mergers in binary evolution models. at the moment, there is no full first-principles model for the development of the ce. we employed the startrack population synthesis code to test the current advancements in studies on the stability of rlof for massive donors to assess their effect on the ligo/virgo source population. in particular, we allowed for more restrictive ce development criteria for massive donors (m > 18 m⊙). we also tested a modified condition for switching between different types of stable mass transfer and between the thermal or nuclear timescale. the implemented modifications significantly influence the basic properties of merging double compact objects, sometimes in non-intuitive ways. for one of the tested models, with restricted ce development criteria, the local merger rate density for bh-bh systems increased by a factor of 2-3 due to the emergence of a new dominant formation scenario without any ce phase. we find that the changes in highly uncertain assumptions on rlof physics may significantly affect: (i) the local merger rate density; (ii) shape of the mass and mass ratio distributions; and (iii) dominant evolutionary formation (with and without ce) scenarios of ligo/virgo sources. our results demonstrate that without sufficiently strong constraints on rlof physics, it is not possible to draw fully reliable conclusions about the population of double compact object systems based on population synthesis studies. | impact of common envelope development criteria on the formation of ligo/virgo sources |
extra c p -violating source for electroweak baryogenesis can dynamically appear at finite temperature in the complex two-higgs doublet model, which might help to alleviate the strong constraints from the electric dipole moment experiments. in this scenario, we study the detailed phase transition dynamics and the corresponding gravitational wave signals in synergy with the collider signals at future lepton colliders. for some parameter spaces, various phase transition patterns can occur, such as the multistep phase transition and supercooling. gravitational waves complementary to collider signals can help to pin down the underlying phase transition dynamics or different phase transition patterns. | gravitational wave and collider signals in complex two-higgs doublet model with dynamical c p -violation at finite temperature |
starting from the observation that artificial neural networks are uniquely suited to solving optimization problems, and most physics problems can be cast as an optimization task, we introduce a novel way of finding a numerical solution to wide classes of differential equations. we find our approach to be very flexible and stable without relying on trial solutions, and applicable to ordinary, partial and coupled differential equations. we apply our method to the calculation of tunneling profiles for cosmological phase transitions, which is a problem of relevance for baryogenesis and stochastic gravitational wave spectra. comparing our solutions with publicly available codes which use numerical methods optimized for the calculation of tunneling profiles, we find our approach to provide at least as accurate results as these dedicated differential equation solvers, and for some parameter choices, even more accurate and reliable solutions. in particular, we compare the neural network approach with two publicly available profile solvers, cosmotransitions and bubbleprofiler, and give explicit examples where the neural network approach finds the correct solution while dedicated solvers do not. we point out that this approach of using artificial neural networks to solve equations is viable for any problem that can be cast into the form f (x →)=0 , and is thus applicable to various other problems in perturbative and nonperturbative quantum field theory. | solving differential equations with neural networks: applications to the calculation of cosmological phase transitions |
dense environments hosting compact binary mergers can leave an imprint on the gravitational-wave emission which, in turn, can be used to identify the characteristics of the environment. to demonstrate such scenario, we consider a simple setup of binary black holes with an environment consisting of a scalar-field bubble. we use this as a proxy for more realistic environments and as an example of the simplest physics beyond the standard model. we perform bayesian inference on the numerical relativity waveforms using state-of-the-art waveform templates for black-hole mergers. in particular, we perform parameter estimation and model selection on signals from black-hole mergers with different mass ratios, total mass and loudness, and hosted by scalar-field bubbles of varying field amplitude. we find that sub-dominant gravitational wave modes emitted during the coalescence and ringdown are key to identifying environmental effects. in particular, we find that for face-on signals dominated by the quadrupole mode, the environment is only detectable if both the ringdown and the late inspiral/early merger fall in the detector band, so that inconsistencies can be found between the inferred binary parameters and those of the final black hole. for edge-on mergers we find that the environment can be detected even if only the ringdown is in band, thanks to the information encoded in the quasi-normal mode structure of the final black-hole. | impact of ringdown higher-order modes on black-hole mergers in dense environments: the scalar field case, detectability and parameter biases |
we study the phenomenology of leptophilic z' gauge bosons at the future high-energy e+e− and μ+μ− colliders, as well as at the gravitational wave observatories. the leptophilic z' model, although well-motivated, remains largely unconstrained from current low-energy and collider searches for z' masses above o (100 gev), thus providing a unique opportunity for future lepton colliders. taking u (1)lα−lβ (α, β = e, μ, τ) models as concrete examples, we show that future e+e− and μ+μ− colliders with multi-tev center-of-mass energies provide unprecedented sensitivity to heavy leptophilic z' bosons. moreover, if these u(1) models are classically scale-invariant, the phase transition at the u(1) symmetry-breaking scale tends to be strongly first-order with ultra-supercooling, and leads to observable stochastic gravitational wave signatures. we find that the future sensitivity of gravitational wave observatories, such as advanced ligo-virgo and cosmic explorer, can be complementary to the collider experiments, probing higher z' masses up to o (104 tev), while being consistent with naturalness and perturbativity considerations. | searching for heavy leptophilic z': from lepton colliders to gravitational waves |
we present the stellar population properties of 69 short gamma-ray burst (grb) host galaxies, representing the largest uniformly modeled sample to date. using the prospector stellar population inference code, we jointly fit photometry and/or spectroscopy of each host galaxy. we find a population median redshift of $z={0.64}_{-0.32}^{+0.83}$ (68% confidence), including nine photometric redshifts at z ≳ 1. we further find a median mass-weighted age of tm= ${0.8}_{-0.53}^{+2.71}$ gyr, stellar mass of log(m */m ⊙) = ${9.69}_{-0.65}^{+0.75}$ , star formation rate of sfr = ${1.44}_{-1.35}^{+9.37}$ m ⊙ yr-1, stellar metallicity of log(z */z ⊙) = $-{0.38}_{-0.42}^{+0.44}$ , and dust attenuation of ${a}_{v}={0.43}_{-0.36}^{+0.85}$ mag (68% confidence). overall, the majority of short grb hosts are star-forming (≈84%), with small fractions that are either transitioning (≈6%) or quiescent (≈10%); however, we observe a much larger fraction (≈40%) of quiescent and transitioning hosts at z ≲ 0.25, commensurate with galaxy evolution. we find that short grb hosts populate the star-forming main sequence of normal field galaxies, but do not include as many high-mass galaxies as the general galaxy population, implying that their binary neutron star (bns) merger progenitors are dependent on a combination of host star formation and stellar mass. the distribution of ages and redshifts implies a broad delay-time distribution, with a fast-merging channel at z > 1 and a decreased neutron star binary formation efficiency from high to low redshifts. if short grb hosts are representative of bns merger hosts within the horizon of current gravitational wave detectors, these results can inform future searches for electromagnetic counterparts. all of the data and modeling products are available on the broadband repository for investigating gamma-ray burst host traits website. | short grb host galaxies. ii. a legacy sample of redshifts, stellar population properties, and implications for their neutron star merger origins |
gravitational waves (gws) are an exciting new probe of physics beyond the standard models of gravity and particle physics. one interesting possibility is provided by the so-called "gravitational atom," wherein a superradiant instability spontaneously forms a cloud of ultralight bosons around a rotating black hole. the presence of these boson clouds affects the dynamics of black hole binary inspirals and their associated gw signals. in this letter, we show that the binary companion can induce transitions between bound and unbound states of the cloud, effectively "ionizing" it, analogous to the photoelectric effect in atomic physics. the orbital energy lost in this process can overwhelm the losses due to gw emission, so that ionization drives the inspiral rather than merely perturbing it. we show that the ionization power contains sharp features that lead to distinctive "kinks" in the evolution of the emitted gw frequency. these discontinuities are a unique signature of the boson cloud, and observing them would not only constitute a detection of the ultralight boson itself, but also provide direct information about its mass and the state of the cloud. | sharp signals of boson clouds in black hole binary inspirals |
we formulate a bayesian framework to analyze ringdown gravitational waves from colliding binary black holes and test the no-hair theorem. the idea hinges on mode cleaning—revealing subdominant oscillation modes by removing dominant ones using newly proposed "rational filters." by incorporating the filter into bayesian inference, we construct a likelihood function that depends only on the mass and spin of the remnant black hole (no dependence on mode amplitudes and phases) and implement an efficient pipeline to constrain the remnant mass and spin without markov chain monte carlo. we test ringdown models by cleaning combinations of different modes and evaluating the consistency between the residual data and pure noise. the model evidence and bayes factor are used to demonstrate the presence of a particular mode and to infer the mode starting time. in addition, we design a hybrid approach to estimate the remnant black hole properties exclusively from a single mode using markov chain monte carlo after mode cleaning. we apply the framework to gw150914 and demonstrate more definitive evidence of the first overtone by cleaning the fundamental mode. this new framework provides a powerful tool for black hole spectroscopy in future gravitational-wave events. | black hole spectroscopy by mode cleaning |
we describe a multi-messenger interpretation of gw170817, which yields a robust lower limit on ns radii. this excludes nss with radii smaller than about 10.7 km and thus rules out very soft nuclear matter. we stress the potential of this type of constraints when future detections become available. for instance, a very similar argumentation may yield an upper bound on the maximum mass of nonrotating nss. we also discuss simulations of ns mergers, which undergo a first-order phase transition to quark matter. we point out a different dynamical behavior. considering the gravitational-wave signal, we identify an unambiguous signature of the qcd phase transition in ns mergers. we show that the occurrence of quark matter through a strong first-order phase transition during merging leads to a characteristic shift of the dominant postmerger frequency. the frequency shift is indicative for a phase transition if it is compared to the postmerger frequency which is expected for purely hadronic eos models. a very strong deviation of several 100 hz is observed for hybrid eoss in an otherwise tight relation between the tidal deformability and the postmerger frequency. in future events the tidal deformability will be inferred with sufficient precision from the premerger phase, while the dominant postmerger frequency can be obtained when current detectors reach a higher sensitivity in the high-frequency range within the next years. finally, we address the potential impact of a first-order phase transition on the electromagnetic counter-part of ns mergers. our simulations suggest that there would be no significant qualitative differences between a system undergoing a phase transition to quark matter and purely hadronic mergers. the quantitative differences are within the spread which is found between different hadronic eos models. this implies on the one hand that gw170817 is compatible with a possible transition to quark matter. on the other hand these considerations show that it may not be easy to identify quantitative differences between purely hadronic mergers and events in which quark matter occurs considering solely their electromagnetic counterpart or their nucleosynthesis products. | equation-of-state constraints and the qcd phase transition in the era of gravitational-wave astronomy |
the successful joint observation of the gravitational wave (gw) event gw170817 and its multiwavelength electromagnetic counterparts enabled us to witness a definite merger event of two neutron stars (nss) for the first time. this historical event confirms the origin of short-duration gamma-ray bursts (grbs) and, in particular, identifies the theoretically predicted kilonova phenomenon that is powered by radioactive decays of r-process heavy elements. however, whether or not a long-lived remnant ns could be formed during this merger event remains unknown; though, such a central engine has been suggested by afterglow observations of some short-duration grbs. by invoking this long-lived remnant ns, we propose a model of hybrid energy sources for the kilonova at 2017gfo associated with gw170817. while the early emission of at 2017gfo is still powered radioactively, as is usually suggested, its late emission is primarily caused by delayed energy injection from the remnant ns. in our model, only one single opacity is required and an intermediate value of κ ≃ 0.97 cm2 g-1 is revealed, which could be naturally provided by lanthanide-rich ejecta that are deeply ionized by the emission from a wind of the ns. these self-consistent results indicate that a long-lived remnant ns, which must have a very stiff equation of state, was formed during the merger event of gw170817. this provides a very stringent constraint on the strong interaction in nuclear-quark matter. it is further implied that such gw events could provide a probe of the early spin and magnetic evolutions of nss, e.g., the burying of surface magnetic fields. | a long-lived remnant neutron star after gw170817 inferred from its associated kilonova |
orbital eccentricity is one of the most robust discriminators for distinguishing between dynamical and isolated formation scenarios of binary black hole mergers using gravitational-wave observatories such as ligo and virgo. using state-of-the-art cluster models, we show how selection effects impact the detectable distribution of eccentric mergers from clusters. we show that the observation (or lack thereof) of eccentric binary black hole mergers can significantly constrain the fraction of detectable systems that originate from dynamical environments, such as dense star clusters. after roughly 150 observations, observing no eccentric binary signals would indicate that clusters cannot make up the majority of the merging binary black hole population in the local universe (95% credibility). however, if dense star clusters dominate the rate of eccentric mergers and a single system is confirmed to be measurably eccentric in the first and second gravitational-wave transient catalogs, clusters must account for at least 14% of detectable binary black hole mergers. the constraints on the fraction of detectable systems from dense star clusters become significantly tighter as the number of eccentric observations grows and will be constrained to within 0.5 dex once 10 eccentric binary black holes are observed. | implications of eccentric observations on binary black hole formation channels |
we point out that dark-energy perturbations may become unstable in the presence of a gravitational wave of sufficiently large amplitude. we study this effect for the cubic horndeski operator (braiding), proportional to αb. the scalar that describes dark-energy fluctuations features ghost and/or gradient instabilities for gravitational-wave amplitudes that are produced by typical binary systems. taking into account the populations of binary systems, we conclude that the instability is triggered in the whole universe for |αb |gtrsim 10-2, i.e. when the modification of gravity is sizeable. the instability is triggered by massive black-hole binaries down to frequencies corresponding to 1010 km: the instability is thus robust, unless new physics enters on even longer wavelengths. the fate of the instability and the subsequent time-evolution of the system depend on the uv completion, so that the theory may end up in a state very different from the original one. the same kind of instability is present in beyond-horndeski theories for |αh| gtrsim 10-20. in conclusion, the only dark-energy theories with sizeable cosmological effects that avoid these problems are k-essence models, with a possible conformal coupling with matter. | dark-energy instabilities induced by gravitational waves |
supersymmetric models with singlet extensions can accommodate single- or multi-step first-order phase transitions (fopt) along the various constituent field directions. such a framework can also produce gravitational waves, detectable at the upcoming space-based interferometers, e.g., u-decigo. we explore the dynamics of electroweak phase transition and the production of gravitational waves in an extended set-up of the next-to-minimal supersymmetric standard model (nmssm) with a standard model singlet right-handed neutrino superfield. we examine the role of the new parameters compared to nmssm on the phase transition dynamics and observe that the occurrence of a fopt, an essential requirement for electroweak baryogenesis, typically favours a right-handed sneutrino state below 125 gev. our investigation shows how the analysis can offer complementary probes for physics beyond the standard model besides the collider searches. | electroweak phase transition in a right-handed neutrino superfield extended nmssm |
we study the postmerger mass ejection of low-mass binary neutron stars (nss) with the system mass of 2.5 m⊙ and subsequent nucleosynthesis by performing general-relativistic, neutrino-radiation viscous-hydrodynamics simulations in axial symmetry. we find that the merger remnants are long-lived massive nss surviving more than several seconds, irrespective of the nuclear equations of state (eoss) adopted. the ejecta masses of our fiducial models are ∼0.06-0.1 m⊙ (depending on the eos), being ∼30% of the initial disk masses (∼0.15-0.3 m⊙). postprocessing nucleosynthesis calculations indicate that the ejecta is composed mainly of light r-process nuclei with small amounts of lanthanides (mass fraction ∼0.002-0.004) and heavier species due to the modest average electron fraction (∼0.32-0.34) for a reasonable value of the viscous coefficient. such abundance distributions are compatible with those in weak r-process stars such as hd 122563 but not with the solar r-process-like abundance patterns found in all measured r-process-enhanced metal-poor stars. therefore, low-mass binary ns mergers should be rare. if such low-mass ns mergers occur, their electromagnetic counterparts, kilonovae, will be characterized by an early bright blue emission because of the large ejecta mass as well as the small lanthanide fraction. we also show, however, that if the effective turbulent viscosity is very high, the electron fraction of the ejecta could be low enough that the solar r-process-like abundance pattern is reproduced and the lanthanide fraction becomes so high that the kilonova would be characterized by early bright blue and late bright red emissions. | postmerger mass ejection of low-mass binary neutron stars |
the ligo-virgo collaboration detection of the binary neutron-star merger event, gw170817, has expanded efforts to understand the equation of state (eos) of nuclear matter. these measurements provide new constraints on the overall pressure, but do not elucidate its origins, by not distinguishing the contribution to the pressure from symmetry energy which governs much of the internal structure of a neutron star. by combining the neutron star eos extracted from the gw170817 event and the eos of symmetric matter from nucleus-nucleus collision experiments, we extract the symmetry pressure, which is the difference in pressure between neutron and nuclear matter over the density region from 1.2ρ0 to 4.5ρ0. while the uncertainties in the symmetry pressure are large, they can be reduced with new experimental and astrophysical results. | symmetry energy constraints from gw170817 and laboratory experiments |
gravitational-wave observations of inspiralling binary neutron-star systems can be used to measure the neutron-star equation of state (eos) through the tidally induced shift in the waveform phase that depends on the tidal deformability parameter λ . previous work has shown that λ , a function of the neutron-star eos and mass, is measurable by advanced ligo for a single event when including tidal information up to the merger frequency. in this work, we describe a method for stacking measurements of λ from multiple inspiral events to measure the eos. we use markov chain monte carlo simulations to estimate the parameters of a four-parameter piecewise-polytrope eos that matches theoretical eos models to a few percent. we find that, for "realistic" event rates (∼40 binary neutron-star inspiral events per year with signal-to-noise ratio >8 in a single advanced ligo detector), combining a year of gravitational-wave data from a three-detector network with the constraints from causality and recent high-mass neutron-star measurements, the eos above nuclear density can be measured to better than a factor of 2 in pressure in most cases. we also find that in the mass range 1 m⊙- 2 m⊙ , the neutron-star radius can be measured to better than ±1 km and the tidal deformability can be measured to better than ±1 ×1 036 g cm2 s2 (10%-50% depending on the eos and mass). the overwhelming majority of this information comes from the loudest ∼5 events. current uncertainties in the post-newtonian waveform model, however, lead to systematic errors in the eos measurement that are as large as the statistical errors, and more accurate waveform models are needed to minimize this error. | reconstructing the neutron-star equation of state with gravitational-wave detectors from a realistic population of inspiralling binary neutron stars |
we study the nonlinear dynamics of binary black hole systems with scalar charge by numerically evolving the full equations of motion for shift-symmetric einstein scalar gauss-bonnet gravity. we consider quasicircular binaries with different mass-ratios, varying the gauss-bonnet coupling and quantifying its impact on the emitted scalar and gravitational waves. we compare our numerical results to post-newtonian calculations of the radiation emitted during the inspiral. we demonstrate the accuracy of the leading-order terms in post-newtonian theory in modeling the amplitude of the scalar waveform, but find that, at least for the last few orbits before merger, the currently available post-newtonian theory is not sufficient to model the dephasing of the gravitational wave signal in this theory. we further find that there is non-negligible nonlinear enhancement in the scalar field at merger, but that the effect on the peak gravitational wave emission is small. | nonlinear studies of binary black hole mergers in einstein-scalar-gauss-bonnet gravity |
understanding the dense matter equation of state at extreme conditions is an important open problem. astrophysical observations of neutron stars promise to solve this, with neutron star interior composition explorer poised to make precision measurements of mass and radius for several stars using the waveform modelling technique. what has been less clear, however, is how these mass-radius measurements might translate into equation of state constraints and what are the associated equation of state sensitivities. we use bayesian inference to explore and contrast the constraints that would result from different choices for the equation of state parametrization; comparing the well-established piecewise polytropic parametrization to one based on physically motivated assumptions for the speed of sound in dense matter. we also compare the constraints resulting from bayesian inference to those from simple compatibility cuts. we find that the choice of equation of state parametrization and particularly its prior assumptions can have a significant effect on the inferred global mass-radius relation and the equation of state constraints. our results point to important sensitivities when inferring neutron star and dense matter properties. this applies also to inferences from gravitational wave observations. | equation of state sensitivities when inferring neutron star and dense matter properties |
context. the recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. it is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes.aims: a promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples, such as the population in 30 doradus in the large magellanic cloud (lmc).methods: with this purpose in mind, we analysed a large grid of detailed binary evolution models at lmc metallicity with initial primary masses between 10 and 40 m⊙, and identified the model systems that potentially evolve into a binary consisting of a black hole and a massive main-sequence star. we then derived the observable properties of such systems, as well as peculiarities of the ob star component.results: we find that ∼3% of the lmc late-o and early-b stars in binaries are expected to possess a black hole companion when stars with a final helium core mass above 6.6 m⊙ are assumed to form black holes. while the vast majority of them may be x-ray quiet, our models suggest that these black holes may be identified in spectroscopic binaries, either by large amplitude radial velocity variations (≳50 km s-1) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity (≳10 km s-1) and simultaneous rapid rotation of the ob star. the predicted mass ratios are such that main-sequence companions can be excluded in most cases. a comparison to the observed ob+wr binaries in the lmc, be and x-ray binaries, and known massive black hole binaries supports our conclusion.conclusions: we expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general and for the formation of double black hole mergers in particular. | properties of ob star-black hole systems derived from detailed binary evolution models |
coalescing massive black hole binaries (mbhbs) of 10^{4-7} m_{\odot }, forming in the aftermath of galaxy mergers, are primary targets of the space mission lisa, the laser interferometer space antenna. an assessment of lisa detection prospects requires an estimate of the abundance and properties of mbhbs that form and evolve during the assembly of cosmic structures. to this aim, we employ a semi-analytic model to follow the co-evolution of mbhbs within their host galaxies. we identify three major evolutionary channels driving the binaries to coalescence: two standard paths along which the binary evolution is driven by interactions with the stellar and/or gaseous environment, and a novel channel where mbhb coalescence occurs during the interaction with a third black hole. for each channel, we follow the orbital evolution of mbhbs with physically motivated models that include a self-consistent treatment of the orbital eccentricity. we find that lisa will detect between ≈25 and ≈75 events per year depending on the seed model. we show that triple-induced coalescences can range from a few detected events up to {∼ } 30{{ per cent}} of the total detected mergers. moreover, even if the standard gas/stars-driven evolutionary channels should fail and mbhbs were to stall, triple interactions would still occur as a result of the hierarchical nature of galaxy formation, resulting in about ≈10 to ≈20 lisa detections per year. remarkably, triple interactions among the black holes can produce coalescing binaries with large eccentricities (≳ 0.9) upon entrance into the lisa band. this eccentricity will remain significant (∼0.1) also at merger, requiring suitable templates for parameter estimation. | post-newtonian evolution of massive black hole triplets in galactic nuclei - iv. implications for lisa |
a strong mountain wave, observed over central europe on 12 january 2016, is simulated in 2d under two fixed background wind conditions representing opposite tidal phases. the aim of the simulation is to investigate the breaking of the mountain wave and subsequent generation of nonprimary waves in the upper atmosphere. the model results show that the mountain wave first breaks as it approaches a mesospheric critical level creating turbulence on horizontal scales of 8-30 km. these turbulence scales couple directly to horizontal secondary waves scales, but those scales are prevented from reaching the thermosphere by the tidal winds, which act like a filter. initial secondary waves that can reach the thermosphere range from 60 to 120 km in horizontal scale and are influenced by the scales of the horizontal and vertical forcing associated with wave breaking at mountain wave zonal phase width, and horizontal wavelength scales. large-scale nonprimary waves dominate over the whole duration of the simulation with horizontal scales of 107-300 km and periods of 11-22 minutes. the thermosphere winds heavily influence the time-averaged spatial distribution of wave forcing in the thermosphere, which peaks at 150 km altitude and occurs both westward and eastward of the source in the 2 ut background simulation and primarily eastward of the source in the 7 ut background simulation. the forcing amplitude is ∼2× that of the primary mountain wave breaking and dissipation. this suggests that nonprimary waves play a significant role in gravity waves dynamics and improved understanding of the thermospheric winds is crucial to understanding their forcing distribution. | secondary gravity waves generated by breaking mountain waves over europe |
gravitational-wave (gw) memory effects are constant changes in the gw strain and its time integrals, which are closely connected to changes in the charges that characterize asymptotically flat spacetimes. the first gw memory effect discovered was a lasting change in the gw strain. it can occur when gws or massless fields carry away 4-momentum from an isolated source. subsequently, it was shown that fluxes of intrinsic angular momentum can generate a new type of memory effect called the spin memory, which is an enduring change in a portion of the time integral of the gw strain. in this paper, we note that there is another new type of memory effect. we call it the "center-of-mass (cm) memory effect," because it is related to changes in the cm part of the angular momentum of a spacetime. we first examine a few properties of the cm angular momentum. specifically, we describe how it transforms under the supertranslation symmetry transformations of the bondi-metzner-sachs group, and we compute a new expression for the flux of cm angular momentum carried by gws in terms of a set of radiative multipole moments of the gw strain. we then turn to the cm memory effect. the cm memory effect appears in a quantity which has the units of the time integral of the gw strain. we define the effect in asymptotically flat spacetimes that start in a stationary state, radiate, and settle to a different stationary state. we show that it is invariant under infinitesimal supertranslation symmetries in this context. to determine the magnitude of the flux of cm angular momentum and the cm memory effect, we compute these quantities for nonspinning, quasicircular compact binaries in the post-newtonian approximation. the cm memory effect arises from terms in the gravitational waveform for such binaries beginning at third and fourth post-newtonian order for unequal- and equal-mass binaries, respectively. finally, we estimate the amplitude of the cm memory effect for these binaries. we anticipate that it will be unlikely for current or upcoming gw detectors to measure the effect. | center-of-mass angular momentum and memory effect in asymptotically flat spacetimes |
in recent years, there have been significant advances in multimessenger astronomy due to the discovery of the first, and so far only confirmed, gravitational wave event with a simultaneous electromagnetic (em) counterpart, as well as improvements in numerical simulations, gravitational wave (gw) detectors, and transient astronomy. this has led to the exciting possibility of performing joint analyses of the gw and em data, providing additional constraints on fundamental properties of the binary progenitor and merger remnant. here, we present a new bayesian framework that allows inference of these properties, while taking into account the systematic modeling uncertainties that arise when mapping from gw binary progenitor properties to photometric light curves. we extend the relative binning method presented in zackay et al. to include extrinsic gw parameters for fast analysis of the gw signal. the focus of our em framework is on light curves arising from r-process nucleosynthesis in the ejected material during and after merger, the so-called kilonova, and particularly on black hole-neutron star systems. as a case study, we examine the recent detection of gw190425, where the primary object is consistent with being either a black hole or a neutron star. we show quantitatively how improved mapping between binary progenitor and outflow properties, and/or an increase in em data quantity and quality are required in order to break degeneracies in the fundamental source parameters. | the challenges ahead for multimessenger analyses of gravitational waves and kilonova: a case study on gw190425 |
we study a scenario where both dark matter and heavy right handed neutrino (rhn) responsible for leptogenesis acquire masses by crossing the relativistic bubble walls formed as a result of a tev scale supercooled first order phase transition (fopt). while this leads to a large out-of-equilibrium abundance of right handed neutrino inside the bubble sufficient to produce the required lepton asymmetry, the dark matter being lighter can still remain in equilibrium with its relic being set by subsequent thermal freeze-out. a classical conformal symmetry ensures the origin of mass via fopt induced by a singlet scalar while also ensuring supercooling leading to enhanced gravitational wave amplitude within the sensitivity of the lisa experiment. a minimal scenario with three rhn, one inert scalar doublet and one singlet scalar as additional fields beyond the standard model is sufficient to realize this possibility which also favours inert rhn dark matter over inert scalar doublet. | leptogenesis and dark matter through relativistic bubble walls with observable gravitational waves |
inspired by the chromo-natural inflation model of adshead&wyman, we reshape its scalar content to relax the tension with current observational bounds. besides an inflaton, the setup includes a spectator sector in which an axion and su(2) gauge fields are coupled via a chern-simons-type term. the result is a viable theory endowed with an alternative production mechanism for gravitational waves during inflation. the gravitational wave signal sourced by the spectator fields can be much larger than the contribution from standard vacuum fluctuations, it is distinguishable from the latter on the basis of its chirality and, depending on the theory parameters values, also its tilt. this production process breaks the well-known relation between the tensor-to-scalar ratio and the energy scale of inflation. as a result, even if the hubble rate is itself too small for the vacuum to generate a tensor amplitude detectable by upcoming experiments, this model still supports observable gravitational waves. | primordial gravitational waves from axion-gauge fields dynamics |
primordial black holes (pbhs) have entered the forefront of theoretical cosmology, due their potential role in phenomena ranging from gravitational waves, to dark matter, to galaxy formation. while producing pbhs from inflationary fluctuations naively would seem to require a large deceleration of the inflaton from its velocity at the horizon exit of cmb scales, in this work we demonstrate that an acceleration from a relatively small downward step in the potential that is transited in much less than an e-fold amplifies fluctuations as well. depending on the location of the step, such pbhs could explain dark matter or the black holes detected by the gravitational wave interferometers. the perturbation enhancement has a natural interpretation as particle production due to the nonadiabatic transition associated with the step, which then leads to amplification in the associated curvature perturbations by the redshifting of the excess kinetic energy after the step, as in an ultra-slow-roll phase. | primordial black holes arise when the inflaton falls |
this second part of the series treats spin ±2 components (or extreme components), that satisfy the teukolsky master equation, of the linearized gravity in the exterior of a slowly rotating kerr black hole. for each of these two components, after performing a first-order differential operator once and twice, the resulting equations together with the teukolsky master equation itself constitute a linear spin-weighted wave system. an energy and morawetz estimate for spin ±2 components is proved by treating this system. this is a first step in a joint work (andersson et al. in stability for linearized gravity on the kerr spacetime, arxiv:1903.03859, 2019) in addressing the linear stability of slowly rotating kerr metrics. | uniform energy bound and morawetz estimate for extreme components of spin fields in the exterior of a slowly rotating kerr black hole ii: linearized gravity |
motivated by the fact that the next-to-minimal supersymmetric standard model is one of the most plausible models that can accommodate electroweak baryogenesis, we analyze its phase structure by tracing the temperature dependence of the minima of the effective potential. our results reveal rich patterns of phase structure that end in the observed electroweak symmetry breaking vacuum. we classify these patterns according to the first transition in their history and show the strong first-order phase transitions that may be possible in each type of pattern. these could allow for the generation of the matter-antimatter asymmetry or potentially observable gravitational waves. for a selection of benchmark points, we checked that the phase transitions completed and calculated the nucleation temperatures. we furthermore present samples that feature strong first-order phase transitions from an extensive scan of the whole parameter space. we highlight common features of our samples, including the fact that the standard model like higgs is often not the lightest higgs in the model. | strong first-order phase transitions in the nmssm — a comprehensive survey |
we show that involving a sterile neutrino species in the λ cdm + r model can help relieve the tension about the tensor-to-scalar ratio r between the planck temperature data and the bicep2 b-mode polarization data. such a model is called the λ cdm + r +νs model in this paper. compared to the λ cdm + r model, there are two extra parameters, neff and mν,sterileeff, in the λ cdm + r +νs model. we show that in this model the tension between planck and bicep2 can be greatly relieved at the cost of the increase of ns. however, comparing with the λ cdm + r + dns / dln k model that can significantly reduce the tension between planck and bicep2 but also makes trouble to inflation due to the large running of the spectral index of the order 10-2 produced, the λ cdm + r +νs model is much better for inflation. by including a sterile neutrino species in the standard cosmology, besides the tension with bicep2, the other tensions of planck with other astrophysical data, such as the h0 direct measurement, the sunyaev-zeldovich cluster counts, and the galaxy shear data, can all be significantly relieved. so, this model seems to be an economical choice. combining the planck temperature data, the wmap-9 polarization data, and the baryon acoustic oscillation data with all these astrophysical data (including bicep2), we find that in the λ cdm + r +νs model ns = 0.999 ± 0.011, r =0.21-0.05+0.04, neff = 3.95 ± 0.33 and mν,sterileeff =0.51-0.13+0.12 ev. thus, our results prefer δneff > 0 at the 2.7σ level and a nonzero mass of sterile neutrino at the 3.9σ level. | sterile neutrinos help reconcile the observational results of primordial gravitational waves from planck and bicep2 |
we report on an all-sky search for continuous gravitational waves in the frequency band 20-2000 hz and with a frequency time derivative in the range of [-1.0 ,+0.1 ] ×10-8 hz /s . such a signal could be produced by a nearby, spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. this search uses the ligo data from the first six months of advanced ligo's and advanced virgo's third observational run, o3. no periodic gravitational wave signals are observed, and 95% confidence-level (c.l.) frequentist upper limits are placed on their strengths. the lowest upper limits on worst-case (linearly polarized) strain amplitude h0 are ∼1.7 ×10-25 near 200 hz. for a circularly polarized source (most favorable orientation), the lowest upper limits are ∼6.3 ×10-26. these strict frequentist upper limits refer to all sky locations and the entire range of frequency derivative values. for a population-averaged ensemble of sky locations and stellar orientations, the lowest 95% c.l. upper limits on the strain amplitude are ∼1.4 ×10-25. these upper limits improve upon our previously published all-sky results, with the greatest improvement (factor of ∼2 ) seen at higher frequencies, in part because quantum squeezing has dramatically improved the detector noise level relative to the second observational run, o2. these limits are the most constraining to date over most of the parameter space searched. | all-sky search for continuous gravitational waves from isolated neutron stars in the early o3 ligo data |
phase transition dynamics may play important roles in the evolution history of the early universe, such as its possible roles in electroweak baryogenesis and dark matter. we systematically discuss and clarify the important details of the phase transition dynamics during a strong first-order phase transition (sfopt). we classify the sfopt into four types: slight supercooling, mild supercooling, strong supercooling, and ultra supercooling. using different characteristic temperatures, length scales and bubble wall velocities, the corresponding gravitational wave (gw) spectra are investigated in details. we emphasize the essential importance of using the correct characteristic temperature and length scale when the phase transition dynamics and gw spectra are calculated. especially, for strong supercooling and ultra supercooling cases, there are obvious differences of the phase transition strength and gw spectra between the results calculated at the nucleation temperature and those derived at the percolation temperature. for ultra supercooling case, we propose a criterion to quantify whether the phase transition can terminate. besides the model-independent discussions, we also study three representative models as concrete examples to clearly show the subtle points therein. | phase transition dynamics and gravitational wave spectra of strong first-order phase transition in supercooled universe |
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