abstract stringlengths 3 192k | title stringlengths 4 857 |
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i propose that the information loss paradox can be resolved by considering the supertranslation of the horizon caused by the ingoing particles. information can be recovered in principle, but it is lost for all practical purposes. | the information paradox for black holes |
investigations on possible violation of lorentz invariance have been widely pursued in the last decades, both from theoretical and experimental sides. a comprehensive framework to formulate the problem is the standard model extension (sme) proposed by a. kostelecky, where violation of lorentz invariance is encoded into specific coefficients. here we present a procedure to link the deformation parameter β of the generalized uncertainty principle to the sme coefficients of the gravity sector. the idea is to compute the hawking temperature of a black hole in two different ways. the first way involves the deformation parameter β , and therefore we get a deformed hawking temperature containing the parameter β . the second way involves a deformed schwarzschild metric containing the lorentz violating terms s¯μ ν of the gravity sector of the sme. the comparison between the two different techniques yields a relation between β and s¯μ ν. in this way bounds on β transferred from s¯μ ν are improved by many orders of magnitude when compared with those derived in other gravitational frameworks. also the opposite possibility of bounds transferred from β to s¯μ ν is briefly discussed. | lorentz violation and generalized uncertainty principle |
the volume behind the black hole horizon was suggested as a holographic dual for the quantum computational complexity of the boundary state in ads/cft. this identification is strongly motivated by the switchback effect: a characteristic delay of complexity growth in reaction to an inserted perturbation, modelled as a shockwave in the bulk. recent proposals of de sitter (ds) holography suggest that a dual theory could be living on a stretched horizon near the cosmological horizon. we study how the spacetime volume behind the cosmological horizon in schwarzschild-ds space reacts to the insertion of shockwaves in an attempt to characterize the properties of this dual theory. we demonstrate that a switchback effect can be observed in ds space. that is, the growth of complexity is delayed in reaction to a perturbation. this delay is longer for earlier shocks and depends on a scrambling time which is logarithmic in the strength of the shockwave and proportional to the inverse temperature of the cosmological ds horizon. this behavior is very similar to what happens for ads black holes, albeit the geometric origin of the effect is somewhat different. | the cosmological switchback effect |
the detection of gravitational waves from compact binary mergers by the ligo/virgo collaboration has, for the first time, allowed us to test relativistic gravity in its strong, dynamical, and nonlinear regime, thus opening a new arena to confront general relativity (and modifications thereof) against observations. we consider a theory which modifies general relativity by introducing a scalar field coupled to a parity-violating curvature term known as dynamical chern-simons gravity. in this theory, spinning black holes are different from their general relativistic counterparts and can thus serve as probes to this theory. we study linear gravito-scalar perturbations of black holes in dynamical chern-simons gravity at leading order in spin and (i) obtain the perturbed field equations describing the evolution of the perturbed gravitational and scalar fields, (ii) numerically solve these equations by direct integration to calculate the quasinormal mode frequencies for the dominant and higher multipoles and tabulate them, (iii) find strong evidence that these rotating black holes are linearly stable, and (iv) present general fitting functions for different multipoles for gravitational and scalar quasinormal mode frequencies in terms of spin and chern-simons coupling parameter. our results can be used to validate the ringdown of small-spin remnants of numerical relativity simulations of black hole binaries in dynamical chern-simons gravity and pave the way towards future tests of this theory with gravitational wave ringdown observations. | quasinormal modes of slowly-rotating black holes in dynamical chern-simons gravity |
we present the first examples in black hole thermodynamics of multicritical phase transitions, in which more than three distinct black hole phases merge at a critical point. working in the context of non-linear electrodynamics, we explicitly present examples of black hole quadruple and quintuple points, and demonstrate how n-tuple critical points can be obtained. our results indicate that black holes can have multiple phases beyond the three types observed so far, resembling the behaviour of multicomponent chemical systems. we discuss the interpretation of our results in the context of the gibbs phase rule. | multi-critical points in black hole phase transitions |
we study extremal non-bps black holes and strings arising in m-theory compactifications on calabi-yau threefolds, obtained by wrapping m2 branes on non-holomorphic 2-cycles and m5 branes on non-holomorphic 4-cycles. using the attractor mechanism we compute the black hole mass and black string tension, leading to a conjectural formula for the asymptotic volumes of connected, locally volume-minimizing representatives of non-holomorphic, even-dimensional homology classes in the threefold, without knowledge of an explicit metric. in the case of divisors we find examples where the volume of the representative corresponding to the black string is less than the volume of the minimal piecewise-holomorphic representative, predicting recombination for those homology classes and leading to stable, non-bps strings. we also compute the central charges of non-bps strings in f-theory via a near-horizon a d s3 limit in 6d which, upon compactification on a circle, account for the asymptotic entropy of extremal non-supersymmetric 5d black holes (i.e., the asymptotic count of non-holomorphic minimal 2-cycles). | non-holomorphic cycles and non-bps black branes |
we study further the duality between semiclassical ads3 and formal cft2 ensembles. first, we study torus wormholes (maldacena-maoz wormholes with two torus boundaries) with one insertion or two insertions on each boundary and find that they give non-decaying contribution to the product of two torus one-point or two-point functions at late-time. second, we study the &z;2 quotients of a torus wormhole such that the outcome has one boundary. we identify quotients that give non-decaying contributions to the torus two-point function at late-time.we comment on reflection (r) or time-reversal (t) symmetry vs. the combination rt that is a symmetry of any relativistic field theory. rt symmetry itself implies that to the extent that a relativistic quantum field theory exhibits random matrix statistics it should be of the goe type for bosonic states and of the gse type for fermionic states. we discuss related implications of these symmetries for wormholes. | more on torus wormholes in 3d gravity |
we introduce a family of partially entangled thermal states in the syk model that interpolates between the thermo-field double state and a pure (product) state. the states are prepared by a euclidean path integral describing the evolution over two euclidean time segments separated by a local scaling operator o . we argue that the holographic dual of this class of states consists of two black holes with their interior regions connected via a domain wall, described by the worldline of a massive particle. we compute the size of the interior region and the entanglement entropy as a function of the scale dimension of o and the temperature of each black hole. we argue that the one-sided bulk reconstruction can access the interior region of the black hole. | expanding the black hole interior: partially entangled thermal states in syk |
context. the connection between black hole, accretion disk, and radio jet can be constrained best by fitting models to observations of nearby low-luminosity galactic nuclei, in particular the well-studied sources sgr a* and m 87. there has been considerable progress in modeling the central engine of active galactic nuclei by an accreting supermassive black hole coupled to a relativistic plasma jet. however, can a single model be applied to a range of black hole masses and accretion rates?aims: here we want to compare the latest three-dimensional numerical model, originally developed for sgr a* in the center of the milky way, to radio observations of the much more powerful and more massive black hole in m 87.methods: we postprocess three-dimensional grmhd models of a jet-producing radiatively inefficient accretion flow around a spinning black hole using relativistic radiative transfer and ray-tracing to produce model spectra and images. as a key new ingredient in these models, we allow the proton-electron coupling in these simulations depend on the magnetic properties of the plasma.results: we find that the radio emission in m 87 is described well by a combination of a two-temperature accretion flow and a hot single-temperature jet. most of the radio emission in our simulations comes from the jet sheath. the model fits the basic observed characteristics of the m 87 radio core: it is "edge-brightened", starts subluminally, has a flat spectrum, and increases in size with wavelength. the best fit model has a mass-accretion rate of ṁ ~ 9 × 10-3m⊙ yr-1 and a total jet power of pj ~ 1043 erg s-1. emission at λ = 1.3 mm is produced by the counter-jet close to the event horizon. its characteristic crescent shape surrounding the black hole shadow could be resolved by future millimeter-wave vlbi experiments.conclusions: the model was successfully derived from one for the supermassive black hole in the center of the milky way by appropriately scaling mass and accretion rate. this suggests the possibility that this model could also apply to a wider range of low-luminosity black holes. | general relativistic magnetohydrodynamical simulations of the jet in m 87 |
we present a new realization of the resonant production of primordial black holes as well as gravitational waves in a two-stage inflation model consisting of a scalar field ϕ with an axion-monodromy-like periodic structure in the potential that governs the first stage and another field χ with a hilltoplike potential that dominates the second stage. the parametric resonance seeded by the periodic structure at the first stage amplifies the perturbations of both fields inside the hubble radius. while the evolution of the background trajectory experiences a turn as the oscillatory barrier height increases, the amplified perturbations of χ remain as they are and contribute to the final curvature perturbation. it turns out that the primordial power spectrum displays a significant resonant peak on small scales, which can lead to an abundant production of primordial black holes. furthermore, gravitational waves are also generated from the resonantly enhanced field perturbations during inflation, the amplitude of which may be constrained by future gravitational wave interferometers. | primordial black holes and gravitational waves from resonant amplification during inflation |
the open question of whether a kerr black hole can become tidally deformed or not has profound implications for fundamental physics and gravitational-wave astronomy. we consider a kerr black hole embedded in a weak and slowly varying, but otherwise arbitrary, multipolar tidal environment. by solving the static teukolsky equation for the gauge-invariant weyl scalar ψ0 and by reconstructing the corresponding metric perturbation in an ingoing radiation gauge, for a general harmonic index ℓ, we compute the linear response of a kerr black hole to the tidal field. this linear response vanishes identically for a schwarzschild black hole and for an axisymmetric perturbation of a spinning black hole. for a nonaxisymmetric perturbation of a spinning black hole, however, the linear response does not vanish, and it contributes to the geroch-hansen multipole moments of the perturbed kerr geometry. as an application, we compute explicitly the rotational black hole tidal love numbers that couple the induced quadrupole moments to the quadrupolar tidal fields, to linear order in the black hole spin, and we introduce the corresponding notion of a tidal love tensor. finally, we show that those induced quadrupole moments are closely related to the well-known physical phenomenon of tidal torquing of a spinning body interacting with a tidal gravitational environment. | tidal love numbers of kerr black holes |
with its exquisite astrometric precision, the latest gaia data release includes $\sim$$10^5$ astrometric binaries, each of which have measured orbital periods, eccentricities, and the thiele-innes orbital parameters. using these and an estimate of the luminous stars' masses, we derive the companion stars' masses, from which we identify a sample of 24 binaries in long period orbits ($p_{\rm orb}\sim{\rm yrs}$) with a high probability of hosting a massive ($>$1.4 $m_{\odot}$), dark companion: a neutron star (ns) or black hole (bh). the luminous stars in these binaries tend to be f-, g-, and k-dwarfs with the notable exception of one hot subdwarf. follow-up spectroscopy of eight of these stars shows no evidence for contamination by white dwarfs or other luminous stars. the dark companions in these binaries span a mass range of 1.35-2.7 $m_{\odot}$ and therefore likely includes both nss and bhs without a significant mass gap in between. furthermore, the masses of several of these objects are $\simeq$1.7 $m_{\odot}$, similar to the mass of at least one of the merging compact objects in gw190425. given that these orbits are too wide for significant mass accretion to have occurred, this sample implies that some nss are born heavy ($\gtrsim$1.5 $m_{\odot}$). additionally, the low orbital velocities ($\lesssim$20 km s$^{-1}$) of these binaries requires that at least some heavy nss receive low natal kicks, otherwise they would have been disrupted during core collapse. although none will become gravitational wave sources within a hubble time, these systems will be exceptionally useful for testing binary evolution theory. | a sample of neutron star and black hole binaries detected through gaia dr3 astrometry |
we apply the classical double-copy procedure to a class of regular, nonsingular black hole solutions. we give several examples, paying particular attention to a string-theory-corrected black hole solution emerging from t-duality. nonperturbative stringy corrections introduce an ultraviolet (uv) zero-point length cutoff which results in nonsingular black hole spacetimes. apart from the uv regulator, the solution is equivalent to the bardeen black hole spacetime. we extend this solution to include an asymptotic de sitter background. all yang-mills field theory quantities associated with the double copy are well-behaved and finite for all values of parameters. we present a thorough analysis of the black hole horizon structure, additionally uncovering a simple yet new connection between horizons on the gravity side and electric fields on the gauge theory side of the double copy. | classical double copy of nonsingular black holes |
in this paper, we present charged dilatonic black holes in gravity's rainbow. we study the geometric and thermodynamic properties of black hole solutions. we also investigate the effects of rainbow functions on different thermodynamic quantities for these charged black holes in dilatonic gravity's rainbow. then we demonstrate that the first law of thermodynamics is valid for these solutions. after that, we investigate thermal stability of the solutions using the canonical ensemble and analyze the effects of different rainbow functions on the thermal stability. in addition, we present some arguments regarding the bound and phase transition points in context of geometrical thermodynamics. we also study the phase transition in extended phase space in which the cosmological constant is treated as the thermodynamic pressure. finally, we use another approach to calculate and demonstrate that the obtained critical points in extended phase space represent a second order phase transition for these black holes. | charged dilatonic black holes in gravity's rainbow |
in this article, we study the shadow produced by rotating black holes having a tidal charge in a randall-sundrum braneworld model, with a cosmological constant. we obtain the apparent shape and the corresponding observables for different values of the tidal charge and the rotation parameter, and we analyze the influence of the presence of the cosmological constant. we also discuss the observational prospects for this optical effect. | shadow cast by rotating braneworld black holes with a cosmological constant |
the monolayer of black phosphorus, or "phosphorene," has recently emerged as a two-dimensional semiconductor with intriguing highly anisotropic transport properties. existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. we perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbation theory and wannier interpolation. our calculation reveals that (1) the high anisotropy provides extra phase space for electron-phonon scattering, and (2) optical phonons have appreciable contributions. both effects cannot be captured by the deformation potential calculations. our simulation predicts carrier mobilities ∼170 c m2/v s for both electrons and holes at 300 k , and a thermoelectric figure of merit z t of up to 0.14 in p -type impurity-free phosphorene at 500 k . | ab initio study of electron-phonon interaction in phosphorene |
we extend recent results on semi-classical conformal blocks in 2d cft and their relation to 3d gravity via the ads/cft correspondence. we consider four-point functions with two heavy and two light external operators, along with the exchange of a light operator. by explicit computation, we establish precise agreement between these cft objects and a simple picture of particle worldlines joined by cubic vertices propagating in asymptotically ads3 geometries (conical defects or btz black holes). we provide a simple argument that explains this agreement. | worldline approach to semi-classical conformal blocks |
the black hole uncertainty principle correspondence suggests that there could exist black holes with mass beneath the planck scale but radius of order the compton scale rather than schwarzschild scale. we present a modified, self-dual schwarzschild-like metric that reproduces desirable aspects of a variety of disparate models in the sub-planckian limit, while remaining schwarzschild in the large mass limit. the self-dual nature of this solution under m ↔ m -1 naturally implies a generalized uncertainty principle with the linear form . we also demonstrate a natural dimensional reduction feature, in that the gravitational radius and thermodynamics of sub-planckian objects resemble that of (1 + 1)-d gravity. the temperature of sub-planckian black holes scales as m rather than m -1 but the evaporation of those smaller than 10-36 g is suppressed by the cosmic background radiation. this suggests that relics of this mass could provide the dark matter. | sub-planckian black holes and the generalized uncertainty principle |
the ligo/virgo collaboration have by now detected the mergers of ten black hole binaries via the emission of gravitational radiation. the hypothesis that these black holes have formed during the cosmic qcd epoch and make up all of the cosmic dark matter, has been rejected by many authors reasoning that, among other constraints, primordial black hole (pbh) dark matter would lead to orders of magnitude larger merger rates than observed. we revisit the calculation of the present pbh merger rate. solar mass pbhs form clusters at fairly high redshifts, which evaporate at lower redshifts. we consider in detail the evolution of binary properties in such clusters due to three-body interactions between the two pbh binary members and a third by-passing pbh, for the first time, by full numerical integration. a monte-carlo analysis shows that formerly predicted merger rates are reduced by orders of magnitude due to such interactions. the natural prediction of pbh dark matter formed during the qcd epoch yields a pronounced peak around 1msolar with a small mass fraction of pbhs on a shoulder around 30msolar, dictated by the well-determined equation of state during the qcd epoch. we employ this fact to make a tentative prediction of the merger rate of ~ 30msolar pbh binaries, and find it very close to that determined by ligo/virgo. furthermore we show that current ligo/virgo limits on the existence of ~ msolar binaries do not exclude qcd pbhs to make up all of the cosmic dark matter. neither do constraints on qcd pbhs from the stochastic gravitational background, pre-recombination accretion, or dwarf galaxies pose a problem. microlensing constraints on qcd pbhs should be re-investigated. we caution, however, in this numerically challenging problem some possibly relevant effects could not be treated. | primordial black hole dark matter and the ligo/virgo observations |
we consider the properties and dynamics of black holes within a family of alternative theories of gravity, namely einstein-maxwell-dilaton theory. we analyze the dynamical evolution of individual black holes as well as the merger of binary black hole systems. we do this for a wide range of parameter values for the family of einstein-maxwell-dilaton theories, investigating, in the process, the stability of these black holes. we examine radiative degrees of freedom, explore the impact of the scalar field on the dynamics of merger, and compare with other scalar-tensor theories. we argue that the dilaton can largely be discounted in understanding merging binary systems and that the end states essentially interpolate between charged and uncharged, rotating black holes. for the relatively small charge values considered here, we conclude that these black hole systems will be difficult to distinguish from their analogs within general relativity. | black hole dynamics in einstein-maxwell-dilaton theory |
we investigate the convergence of relativistic hydrodynamics in charged fluids, within the framework of holography. on the one hand, we consider the analyticity properties of the dispersion relations of the hydrodynamic modes on the complex frequency and momentum plane and on the other hand, we perform a perturbative expansion of the dispersion relations in small momenta to a very high order. we see that the locations of the branch points extracted using the first approach are in good quantitative agreement with the radius of convergence extracted perturbatively. we see that for different values of the charge, different types of pole collisions set the radius of convergence. the latter turns out to be finite in the neutral case for all hydrodynamic modes, while it goes to zero at extremality for the shear and sound modes. furthermore, we also establish the phenomenon of pole-skipping for the reissner-nordström black hole, and we find that the value of the momentum for which this phenomenon occurs need not be within the radius of convergence of hydrodynamics. | quasinormal modes in charged fluids at complex momentum |
we construct ads4 × σ and ads2 × σ × σg solutions in f(4) gauged supergravity in six dimensions, where σ is a two dimensional manifold of non-constant curvature with conical singularities at its two poles, called a spindle, and σg is a constant curvature riemann surface of genus g . we find that the first solution realizes a "topologically topological twist", while the second class of solutions gives rise to an "anti twist". we compute the holographic free energy of the ads4 × σ solution and find that it matches the entropy computed by extremizing an entropy functional that is constructed by gluing gravitational blocks. for the ads2 × σ × σg solution, we find that the bekenstein-hawking entropy is reproduced by extremizing an appropriately defined entropy functional, which leads us to conjecture that this solution is dual to a three dimensional scft on a spindle. a class of the ads2 × σ × σg solutions can be embedded in four dimensional t3 gauged supergravity, which is a subtruncation of the six dimensional theory. | black holes with spindles at the horizon |
we investigate the two-stage inflation regime in the theory of hybrid cosmological α-attractors. the spectrum of inflationary perturbations is compatible with the latest planck/bicep/keck array results, thanks to the attractor properties of the model. however, at smaller scales, it may have a very high peak of controllable width and position, leading to a copious production of primordial black holes (pbh) and generation of a stochastic background of gravitational waves (sgwb). | hybrid α-attractors, primordial black holes and gravitational wave backgrounds |
we present a doubly holographic prescription for computing entanglement entropy on a gravitating brane. it involves a ryu-takayanagi surface with a dirichlet anchoring condition. in braneworld cosmology, a related approach was used previously in arxiv:2007.06551. there, the prescription naturally computed a co-moving entanglement entropy, and was argued to resolve the information paradox for a black hole living in the cosmology. in this paper, we show that the dirichlet prescription leads to reasonable results, when applied to a recently studied wedge holography set up with a gravitating bath. the nature of the information paradox and its resolution in our dirichlet problem have a natural understanding in terms of the strength of gravity on the two branes and at the anchoring location. by sliding the anchor to the defect, we demonstrate that the limit where gravity decouples from the anchor is continuous — in other words, as far as island physics is considered, weak gravity on the anchor is identical to no gravity. the weak and (moderately) strong gravity regions on the brane are separated by a "dirichlet wall". we find an intricate interplay between various extremal surfaces, with an island coming to the rescue whenever there is an information paradox. this is despite the presence of massless gravitons in the spectrum. the overall physics is consistent with the slogan that gravity becomes "more holographic", as it gets stronger. our observations strengthen the case that the conventional page curve is indeed of significance, when discussing the information paradox in flat space. we work in high enough dimensions so that the graviton is non-trivial, and our results are in line with the previous discussions on gravitating baths in arxiv:2005.02993 and arxiv:2007.06551. | dirichlet baths and the not-so-fine-grained page curve |
the effect of spacetime curvature on optical properties may provide an opportunity to suggest new tests for gravity theories. in this paper, we investigated gravitational weak lensing around a bardeen black hole with the string clouds parameter. first, we examined the horizon structure in the presence of string clouds around the gravitational compact object defined by bardeen spacetime. the effect of gravitational weak lensing in a plasma medium is also discussed. according to the findings, the influence of the string cloud parameter on the circular orbits of a light ray around the black hole is greater than that in the schwarzschild case, while the influence of the charge is reversed. the deflection angle of light rays in weak lensing is also used to study how much the image is magnified. | weak gravitational lensing around bardeen black hole with a string cloud in the presence of plasma |
we investigate the weak cosmic censorship conjecture in kerr-(anti-)de sitter black holes under the scattering of a scalar field. we test the conjecture in terms of whether the black hole can exceed the extremal condition with respect to its change caused by the energy and angular momentum fluxes of the scalar field. without imposing the laws of thermodynamics, we prove that the conjecture is valid in all the initial states of the black hole (non-extremal, near-extremal, and extremal black holes). the validity in the case of the near-extremal black hole is different from the results of similar tests conducted by adding a particle because the fluxes represent the energy and angular momentum transferred to the black hole during the time interval not included in the tests involving the particle. using the time interval, we show that the angular velocity of the black hole with the scalar field of a constant state takes a long time for saturation to the frequency of the scalar field. | weak cosmic censorship conjecture in kerr-(anti-)de sitter black hole with scalar field |
we obtain the holographic entanglement negativity for bipartite mixed states at a finite temperature in baths described by conformal field theories dual to configurations involving two communicating black holes in a braneworld geometry. in this context, we analyze the mixed state entanglement structure characterized by the information transfer between the black holes. the model corresponds to a configuration of two dimensional eternal jackiw-teitelboim (jt) black holes in a braneworld geometry involving two planck branes coupled through shared bath systems described by cft2s . our results reproduce analogue of the page curves for the entanglement negativity obtained earlier in the context of random matrix theory and from geometric evaporation in jt black hole configurations. | islands for entanglement negativity in communicating black holes |
using the complexity=action framework, we compute the late time growth of complexity for charged black holes in lovelock gravity. our calculation is facilitated by the fact that the null boundaries of the wheeler-dewitt patch do not contribute at late times and essential contributions coming from the joints are now understood. the late time growth rate reduces to a difference of internal energies associated with the inner and outer horizons, and in the limit where the mass is much larger than the charge, we reproduce the celebrated result of 2 m /π with corrections proportional to the highest lovelock coupling in even (boundary) dimensions. we find in some cases a minimum mass below which complexity remains effectively constant, even if the black hole contains a nondegenerate horizon. | complexity growth rate in lovelock gravity |
it is conventional to study the entanglement between spatial regions of a quantum field theory. however, in some systems entanglement can be dominated by "internal", possibly gauged, degrees of freedom that are not spatially organized, and that can give rise to gaps smaller than the inverse size of the system. in a holographic context, such small gaps are associated to the appearance of horizons and singularities in the dual spacetime. here, we propose a concept of entwinement, which is intended to capture this fine structure of the wavefunction. holographically, entwinement probes the entanglement shadow — the region of spacetime not probed by the minimal surfaces that compute spatial entanglement in the dual field theory. we consider the simplest example of this scenario — a 2d conformal field theory (cft) that is dual to a conical defect in ads3 space. following our previous work, we show that spatial entanglement in the cft reproduces spacetime geometry up to a finite distance from the conical defect. we then show that the interior geometry up to the defect can be reconstructed from entwinement that is sensitive to the discretely gauged, fractionated degrees of freedom of the cft. entwinement in the cft is related to non-minimal geodesics in the conical defect geometry, suggesting a potential quantum information theoretic meaning for these objects in a holographic context. these results may be relevant for the reconstruction of black hole interiors from a dual field theory. | entwinement and the emergence of spacetime |
we compute the on-shell euclidean action of schwarzschild-de sitter black holes, and take their contributions in the gravitational path integral into account using the formalism of constrained instantons. although euclidean de sitter black hole geometries have conical singularities for generic masses, their on-shell action is finite and is shown to be independent of the euclidean time periodicity and equal to minus the sum of the black hole and cosmological horizon entropy. we apply this result to compute the probability for a nonrotating, neutral arbitrary mass black hole to nucleate spontaneously in empty de sitter space, which separates into a constant and a "non-perturbative" contribution, the latter corresponding to the proper saddle-point instanton in the nariai limit. we also speculate on some further applications of our results, most notably as potential non-perturbative corrections to correlators in the de sitter vacuum. | on the euclidean action of de sitter black holes and constrained instantons |
this is the last part of our proof of the nonlinear stability of the kerr family for small angular momentum, i.e $|a|/m\ll 1$, in which we deal with the nonlinear wave type estimates needed to complete the project. more precisely we provide complete proofs for theorems m1 and m2 as well the curvature estimates of theorem m8, which were stated without proof in sections 3.7.1 and 9.4.7 of \cite{ks:kerr}. our procedure is based on a new general interest formalism (detailed in part i of this work), which extends the one used in the stability of minkowski space. together with \cite{ks:kerr} and the gcm papers \cite{ks-gcm1}, \cite{ks-gcm2}, \cite{shen}, this work completes proof of the main theorem stated in section 3.4 of \cite{ks:kerr}. | wave equations estimates and the nonlinear stability of slowly rotating kerr black holes |
ultralight scalar fields around spinning black holes can trigger superradiant instabilities, forming a long-lived bosonic condensate outside the horizon. we use numerical solutions of the perturbed field equations and astrophysical models of massive and stellar-mass black hole populations to compute, for the first time, the stochastic gravitational-wave background from these sources. in optimistic scenarios the background is observable by advanced ligo and lisa for field masses ms in the range ∼[2 ×10-13,10-12] and ∼5 ×[10-19,10-16] ev , respectively, and it can affect the detectability of resolvable sources. our estimates suggest that an analysis of the stochastic background limits from ligo o1 might already be used to marginally exclude axions with mass ∼10-12.5 ev . semicoherent searches with advanced ligo (lisa) should detect ∼15 (5 ) to 200(40) resolvable sources for scalar field masses 3 ×10-13 (10-17) ev . lisa measurements of massive bh spins could either rule out bosons in the range ∼[10-18,2 ×10-13] ev , or measure ms with 10% accuracy in the range ∼[10-17,10-13] ev . | stochastic and resolvable gravitational waves from ultralight bosons |
in this paper we present a new black hole solution surrounded by dark matter (dm) halo in the galactic center using the mass model of m87 and that coming from the universal rotation curve (urc) dark matter profile representing family of spiral galaxies. in both cases the dm halo density is cored with a size r0 and a central density ρ0: ρ (r )=ρ0/(1 +r /r0)(1 +(r /r0)2). since r0ρ0=120 m⊙/pc2 [mon. not. r. astron. soc. 397, 1169 (2009), 10.1111/j.1365-2966.2009.15004.x], then by varying the central density one can reproduce the dm profile in any spiral. using the newman-jains method we extend our solution to obtain a rotating black hole surrounded by dark matter halo. we find that the apparent shape of the shadow beside the black hole spin a , it also depends on the central density of the surrounded dark matter ρ0. as a specific example we consider the galaxy m87, with a central density ρ0=6.9 ×106 m⊙/kpc3 and a core radius r0=91.2 kpc . in the case of m87, our analyses show that the effect of dark matter on the size of the black hole shadow is almost negligible compared to the shadow size of the kerr vacuum solution hence the angular diameter 42 μ as remains almost unaltered when the dark matter is considered. for a small totally dark matter dominated spiral such as ugc 7232, we find similar effect of dark matter on the shadow images compared to the m87. however, in specific conditions having a core radius comparable to the black hole mass and dark matter with very high density, we show that the shadow images decreases compared to the kerr vacuum black hole. the effect of dark matter on the apparent shadow shape can shed some light in future observations as an indirect way to detect dark matter using the shadow images. | black hole surrounded by a dark matter halo in the m87 galactic center and its identification with shadow images |
we study the harvesting of correlations by two unruh-dewitt static detectors from the vacuum state of a massless scalar field in a background vaidya spacetime consisting of a collapsing null shell that forms a schwarzschild black hole (hereafter vaidya spacetime for brevity), and we compare the results with those associated with the three preferred vacua (boulware, unruh, hartle-hawking-israel vacua) of the eternal schwarzschild black hole spacetime. to do this we make use of the explicit wightman functions for a massless scalar field available in (1+1)-dimensional models of the collapsing spacetime and schwarzschild spacetimes, and the detectors couple to the proper time derivative of the field. first we find that, with respect to the harvesting protocol, the unruh vacuum agrees very well with the vaidya vacuum near the horizon even for finite-time interactions. second, all four vacua have different capacities for creating correlations between the detectors, with the vaidya vacuum interpolating between the unruh vacuum near the horizon and the boulware vacuum far from the horizon. third, we show that the black hole horizon inhibits any correlations, not just entanglement. finally, we show that the efficiency of the harvesting protocol depend strongly on the signalling ability of the detectors, which is highly non-trivial in presence of curvature. we provide an asymptotic analysis of the vaidya vacuum to clarify the relationship between the boulware/unruh interpolation and the near/far from horizon and early/late-time limits. we demonstrate a straightforward implementation of numerical contour integration to perform all the calculations. | harvesting correlations in schwarzschild and collapsing shell spacetimes |
next-generation detectors are expected to be sensitive to postmerger signals from binary neutron star coalescences and thus to directly probe the remnant dynamics. we investigate the scientific potential of postmerger detections with the einstein telescope using full bayesian analyses with the state-of-the-art waveform model ${\tt nrpmw}$. we find that: (i) postmerger signals with signal-to-noise ratio (snr) ${\sim}7$ can be confidently detected with a bayes' factor of $\log{\cal b}\simeq 5$ ($\rm e$-folded) and the posterior distributions report informative measurements already at snr ${\sim}6$ for some noise realizations. (ii) the postmerger peak frequency $f_2$ can be confidently identified at snr $7$ with errors of $o(1~{\rm khz})$, that decrease below $o(100~{\rm hz})$ for snr 10. (iii) the remnant's time of collapse to black hole can be constrained to $o(20~{\rm ms})$ at snr 10. however, the inference can be biased by noise fluctuationsif the latter exceed the signal's amplitude before collapse. (iv) violations of the eos-insentive relations for $f_2$ can be detected at snr $\gtrsim 8$ if the frequency shifts are $\gtrsim 500~{\rm hz}$; they can be smoking guns for eos softening effects at extreme densities. however, the $f_2$ measurement can be significantly biased by subdominant frequency components for short-lived remnants. in these cases, an eos softening might be better inferred from the remnant's earlier collapse. | kilohertz gravitational waves from binary neutron star mergers: inference of postmerger signals with the einstein telescope |
in this work we consider the observational properties of compact boson stars with self-interactions orbited by isotropically emitting (hot-spot) sources and optically thin accretion disks. we consider two families of boson stars supported by quartic and sixth-order self-interaction potentials, and choose three samples of each of them in growing compactness; only those with large enough compactness are capable to hold light rings, namely, null bound orbits. for the hot spots, using inclination angles θ ={2 0 ° ,5 0 ° ,8 0 ° } we find a secondary track plunge-through image of photons crossing the interior of the boson star, which can be further decomposed into additional images if the star is compact enough. for accretion disks we find that the latter class of stars actually shows a sequence of additional secondary images in agreement with the hot-spot analysis, a feature absent in typical black hole space-times. furthermore, we also find a shadowlike central brightness depression for some of these stars in both axial observations and at the inclination angles above. we discuss our findings in relation to the capability of boson stars to effectively act as black hole mimickers in their optical appearances as well as potential observational discriminators. | imaging compact boson stars with hot spots and thin accretion disks |
gravitational waves (gws) are inevitably produced by second-order terms in cosmological perturbation theory. most notably, the so-called induced (gws) are a window to the small scales part of the primordial spectrum of fluctuations and a key counterpart to the primordial black hole (pbh) scenario. however, semi-analytical solutions are only known for matter and radiation domination eras. in this paper, we present new analytic integral formulas for the induced gws on subhorizon scales in a general cosmological background with a constant equation-of-state. we also discuss applications to a peaked primordial scalar power spectrum and the pbh scenario. | induced gravitational waves in a general cosmological background |
the black hole information paradox is among the most outstanding puzzles in physics. i argue here there is yet another black hole quandary which, in light of the recent direct detection of gravitational waves by advanced ligo, reveals a new window to probe the nature of spacetime in the forthcoming era of 'precision gravity.' | the tune of love and thenature(ness)of spacetime |
we show that nearly half of all binary black hole (bbh) mergers dynamically assembled in globular clusters have measurable eccentricities (e > 0.01) in the lisa band (10-2 hz), when general relativistic corrections are properly included in the n-body evolution. if only newtonian gravity is included, the derived fraction of eccentric lisa sources is significantly lower, which explains why recent studies all have greatly underestimated this fraction. our findings have major implications for how to observationally distinguish between bbh formation channels using eccentricity with lisa, which is one of the key science goals of the mission. we illustrate that the relatively large population of eccentric lisa sources reported here originates from bbhs that merge between hardening binary-single interactions inside their globular cluster. these results indicate a bright future for using lisa to probe the origin of bbh mergers. | black hole mergers from globular clusters observable by lisa i: eccentric sources originating from relativistic n-body dynamics |
we study the superradiant instability of a massive boson around a spinning black hole in full general relativity without assuming spatial symmetries. we focus on the case of a rapidly spinning black hole in the presence of a vector boson with a compton wavelength comparable to the black hole radius, which is the regime where relativistic effects are maximized. we follow the growth of the boson cloud through superradiance into the nonlinear regime as it spins down the black hole, reaches a maximum energy, and begins to dissipate through the emission of gravitational waves. we find that the superradiant instability can efficiently convert a significant fraction of a black hole's rotational energy into gravitational radiation. | massive boson superradiant instability of black holes: nonlinear growth, saturation, and gravitational radiation |
in the past years, black holes and the fate of their singularity have been heavily studied within loop quantum gravity. effective spacetime descriptions incorporating quantum geometry corrections are provided by the so-called polymer models. despite the technical differences, the main common feature shared by these models is that the classical singularity is resolved by a black-to-white hole transition. in a recent paper (bodendorfer et al 2019 class. quantum grav. 36 195015), we discussed the existence of two dirac observables in the effective quantum theory respectively corresponding to the black and white hole mass. physical requirements about the onset of quantum effects then fix the relation between these observables after the bounce, which in turn corresponds to a restriction on the admissible initial conditions for the model. in the present paper, we discuss in detail the role of such observables in black hole polymer models. first, we revisit previous models and analyse the existence of the dirac observables there. observables for the horizons or the masses are explicitly constructed. in the classical theory, only one dirac observable has physical relevance. in the quantum theory, we find a relation between the existence of two physically relevant observables and the scaling behaviour of the polymerisation scales under fiducial cell rescaling. we present then a new model based on polymerisation of new variables which allows to overcome previous restrictions on initial conditions. quantum effects cause a bound of a unique kretschmann curvature scale, independently of the relation between the two masses. | mass and horizon dirac observables in effective models of quantum black-to-white hole transition |
the effect of the number of stacking layers and the type of stacking on the electronic and optical properties of bilayer and trilayer black phosphorus are investigated by using first-principles calculations within the framework of density functional theory. we find that inclusion of many-body effects (i.e., electron-electron and electron-hole interactions) modifies strongly both the electronic and optical properties of black phosphorus. while trilayer black phosphorus with a particular stacking type is found to be a metal by using semilocal functionals, it is predicted to have an electronic band gap of 0.82 ev when many-body effects are taken into account within the g0w0 scheme. though different stacking types result in similar energetics, the size of the band gap and the optical response of bilayer and trilayer phosphorene are very sensitive to the number of layers and the stacking type. regardless of the number of layers and the type of stacking, bilayer and trilayer black phosphorus are direct band gap semiconductors whose band gaps vary within a range of 0.3 ev. stacking arrangements that are different from the ground state structure in both bilayer and trilayer black phosphorus exhibit significant modified valence bands along the zigzag direction and result in larger hole effective masses. the optical gap of bilayer (trilayer) black phosphorus varies by 0.4 (0.6) ev when changing the stacking type. the calculated binding energy of the bound exciton hardly changes with the type of stacking and is found to be 0.44 (0.30) ev for bilayer (trilayer) phosphorous. | significant effect of stacking on the electronic and optical properties of few-layer black phosphorus |
in the present work we study the scale dependence at the level of the effective action of charged black holes in einstein-maxwell as well as in einstein-power-maxwell theories in (2+1)-dimensional spacetimes without a cosmological constant. we allow for scale dependence of the gravitational and electromagnetic couplings, and we solve the corresponding generalized field equations imposing the null energy condition. certain properties, such as horizon structure and thermodynamics, are discussed in detail. | scale-dependent three-dimensional charged black holes in linear and non-linear electrodynamics |
we compute cosmic microwave background (cmb) anisotropy constraints on exotic forms of energy injection in electromagnetic (e.m.) channels over a large range of timescales. we show that these constraints are very powerful around or just after recombination, although cmb keeps some sensitivity e.g. to decaying species with lifetimes as long as 1025 s. these bounds are complementary to cmb spectral distortions and primordial nucleosynthesis ones, which dominate at earlier timescales, as we also review here. for the first time, we describe the effects of the e.m. energy injection on the cmb power spectra as a function of the injection epoch, using the lifetime of a decaying particle as proxy. we also identify a suitable on-the-spot approximation, that can be used to derive accurate constraints, and describe its differences with the most up-to-date treatment. our results are of interest not only for early universe relics constituting (a fraction of) the dark matter, but also for other exotic injection of e.m. radiation. for illustration, we apply our formalism to: i) primordial black holes of mass 1013.5 g lesssim m lesssim 1016.8 g, showing that the constraints are comparable to the ones obtained from gamma-ray background studies and even dominate below ~ 1014 g. ii) to a peculiar mass-mixing range in the sterile neutrino parameter space, complementary to other astrophysical and laboratory probes. iii) finally, we provide a first estimate of the room for improvement left for forthcoming 21 cm experiments, comparing it with the reach of proposed cmb spectral distortion (pixie) and cmb angular power spectrum (core) missions. we show that the best and most realistic opportunity to look for this signal (or to improve over current constraints) in the 21 cm probe is to focus on the cosmic dawn epoch, 15 lesssim z lesssim 30, where the qualitatively unambiguous signature of a spectrum in emission can be expected for models that evade all current constraints. | cosmological constraints on exotic injection of electromagnetic energy |
accretion discs around supermassive black holes are promising sites for stellar mass black hole mergers detectable with ligo. here we present the results of monte carlo simulations of black hole mergers within 1-d agn disc models. for the spin distribution in the disc bulk, key findings are: (1) the distribution of χeff is naturally centred around $\tilde{\chi }_{\rm eff} \approx 0.0$ , (2) the width of the χeff distribution is narrow for low natal spins. for the mass distribution in the disc bulk, key findings are: (3) mass ratios $\tilde{q} \sim 0.5\!-\!0.7$ , (4) the maximum merger mass in the bulk is $\sim 100\!-\!200\, \mathrm{m}_{\odot }$ , (5) $\sim 1{{\ \rm per\ cent}}$ of bulk mergers involve bh $\gt 50\, \mathrm{m}_{\odot }$ with (6) $\simeq 80{{\ \rm per\ cent}}$ of bulk mergers are pairs of first generation bh. additionally, mergers at a migration trap grow an imbh with typical merger mass ratios $\tilde{q}\sim 0.1$ . ongoing ligo non-detections of black holes $\gt 10^{2}\, \mathrm{m}_{\odot }$ puts strong limits on the presence of migration traps in agn discs (and therefore agn disc density and structure) as well as median agn disc lifetime. the highest merger rate occurs for this channel if agn discs are relatively short-lived (≤1 myr) so multiple agn episodes can happen per galactic nucleus in a hubble time. | monte carlo simulations of black hole mergers in agn discs: low χeff mergers and predictions for ligo |
the spherically symmetric deformation of the schwarzschild solution owing to the quantum corrections to gravity is known as kazakov-solodukhin black-hole metric. neglecting non-spherical deformations of the background the problem was solved non-perturbatively. here we analyze the basic characteristics of this geometry, such as: quasinormal modes and grey-body factors of fields of various spin and shadow cast by this black hole. the wkb approach and time-domain integration method, which we used for calculation of quasinormal modes, are in a good concordance. the analytical formula for quasinormal modes is deduced in the eikonal regime. the radius of shadow is decreasing when the quantum deformation is turned on. | quantum corrected black holes: quasinormal modes, scattering, shadows |
identifying an entanglement island requires exquisite control over the entropy of quantum fields, which is available only in toy models. here we present a set of sufficient conditions that guarantee the existence of an island and place an upper bound on the entropy computed by the island rule. this is enough to derive the main features of the page curve for an evaporating black hole in any spacetime dimension. our argument makes use of wall's maximin formulation and the quantum focusing conjecture. as a corollary, we derive a novel entropy bound. | island finder and entropy bound |
black hole (bh) accretion discs formed in compact-object mergers or collapsars may be major sites of the rapid-neutron-capture (r-)process, but the conditions determining the electron fraction (ye) remain uncertain given the complexity of neutrino transfer and angular-momentum transport. after discussing relevant weak-interaction regimes, we study the role of neutrino absorption for shaping ye using an extensive set of simulations performed with two-moment neutrino transport and again without neutrino absorption. we vary the torus mass, bh mass and spin, and examine the impact of rest-mass and weak-magnetism corrections in the neutrino rates. we also test the dependence on the angular-momentum transport treatment by comparing axisymmetric models using the standard α-viscosity with viscous models assuming constant viscous length-scales (lt) and 3d magnetohydrodynamic (mhd) simulations. finally, we discuss the nucleosynthesis yields and basic kilonova properties. we find that absorption pushes ye towards ~0.5 outside the torus, while inside increasing the equilibrium value $y_\mathrm{ e}^{\mathrm{eq}}$ by ~0.05-0.2. correspondingly, a substantial ejecta fraction is pushed above ye = 0.25, leading to a reduced lanthanide fraction and a brighter, earlier, and bluer kilonova than without absorption. more compact tori with higher neutrino optical depth, τ, tend to have lower $y_\mathrm{ e}^{\mathrm{eq}}$ up to τ ~ 1-10, above which absorption becomes strong enough to reverse this trend. disc ejecta are less (more) neutron rich when employing an lt = const. viscosity (mhd treatment). the solar-like abundance pattern found for our mhd model marginally supports collapsar discs as major r-process sites, although a strong r-process may be limited to phases of high mass-infall rates, $\dot{m}\, \, \raise0.14em\rm{\gt }\lower0.28em\rm{\sim }\, \, 2\times 10^{-2}$ m⊙ s-1. | neutrino absorption and other physics dependencies in neutrino-cooled black hole accretion discs |
we present a class of charged black hole solutions in an (n +2 )-dimensional massive gravity with a negative cosmological constant, and study the thermodynamics and phase structure of the black hole solutions in both the grand canonical and canonical ensembles. the black hole horizon can have a positive, zero, or negative constant curvature characterized by the constant k . by using the hamiltonian approach, we obtain conserved charges of the solutions and find that the black hole entropy still obeys the area formula and the gravitational field equation at the black hole horizon can be cast into a form similar to the first law of black hole thermodynamics. in the grand canonical ensemble, we find that the thermodynamics and phase structure depend on the combination k -μ2/4 +c2m2 in the four-dimensional case, where μ is the chemical potential and c2m2 is the coefficient of the second term in the potential associated with the graviton mass. when it is positive, the hawking-page phase transition can happen; when as it is negative, the black hole is always thermodynamically stable with a positive capacity. in the canonical ensemble, the combination turns out to be k +c2m2 in the four-dimensional case. when it is positive, a first-order phase transition can happen between small and large black holes if the charge is less than its critical value. in the higher-dimensional [(n +2 )≥5 ] case, even when the charge is absent, the small/large black hole phase transition can also appear, and the coefficients for the third (c3m2) and/or fourth (c4m2) terms in the potential associated with the graviton mass in massive gravity can play the same role as that of the charge in the four-dimensional case. | thermodynamics of black holes in massive gravity |
quantum speed limits set an upper bound to the rate at which a quantum system can evolve, and as such can be used to analyze the scrambling of information. to this end, we consider the survival probability of a thermofield double state under unitary time evolution which is related to the analytic continuation of the partition function. we provide an exponential lower bound to the survival probability with a rate governed by the inverse of the energy fluctuations of the initial state. further, we elucidate universal features of the nonexponential behavior at short and long times of evolution that follow from the analytic properties of the survival probability and its fourier transform, both for systems with a continuous and for systems with a discrete energy spectrum. we find the spectral form factor in a number of illustrative models; notably, we obtain the exact answer in the gaussian unitary ensemble for any n with excellent agreement with recent numerical studies. we also discuss the relationship of our findings to models of black hole information loss, such as the sachdev-ye-kitaev model dual to ads2 , as well as higher-dimensional versions of ads/cft. | scrambling the spectral form factor: unitarity constraints and exact results |
we consider the effect of quantum diffusion on the dynamics of the inflaton during a period of ultra-slow-roll inflation. we extend the stochastic-$\delta\mathcal{n}$ formalism to the ultra-slow-roll regime and show how this system can be solved analytically in both the classical-drift and quantum-diffusion dominated limits. by deriving the characteristic function, we are able to construct the full probability distribution function for the primordial density field. in the diffusion-dominated limit, we recover an exponential tail for the probability distribution, as found previously in slow-roll inflation. to complement these analytical techniques, we present numerical results found both by very large numbers of simulations of the langevin equations, and through a new, more efficient approach based on iterative volterra integrals. we illustrate these techniques with two examples of potentials that exhibit an ultra-slow-roll phase leading to the possible production of primordial black holes. | ultra-slow-roll inflation with quantum diffusion |
we compute the superconformal index of 3d n = 2 superconformal field theories obtained from n m5-branes wrapped on a hyperbolic 3-manifold. exploiting the 3d-3d correspondence, we use perturbative invariants of sl(n, ℂ) chern-simons theory to determine the superconformal index in the large n limit, including corrections logarithmic in n . the leading order partition function provides a microscopic foundation for the entropy function of the dual rotating asymptotically ads4 black holes. we also verify that the supergravity one-loop contribution to the log n term coincides with the field theoretic result. we propose a 3d-3d formulation for the refined topologically twisted index, and provide strong evidence in support of its vanishing - which agrees with the fact that the expected dual rotating magnetically-charged black hole does not exist. this provides an interesting link between gravity and a tantalizing mathematical result. | rotating black hole entropy from m5-branes |
novel static black hole solutions with electric and magnetic charges are derived for the class of modified gravities: f (r ) =r +2 β √{r } , with or without a cosmological constant. the new black holes behave asymptotically as flat or (a)ds space-times with a dynamical value of the ricci scalar given by r =1/r2 and r =8/r2λ +1 r2 , respectively. they are characterized by three parameters, namely their mass and electric and magnetic charges, and constitute black hole solutions different from those in einstein's general relativity. their singularities are studied by obtaining the kretschmann scalar and ricci tensor, which shows a dependence on the parameter β that is not permitted to be zero. a conformal transformation is used to display the black holes in einstein's frame and check if its physical behavior is changed w.r.t. the jordan one. to this end, thermodynamical quantities, as the entropy, hawking temperature, quasi-local energy, and the gibbs free energy are calculated to investigate the thermal stability of the solutions. also, the casual structure of the new black holes is studied, and a stability analysis is performed in both frames using the odd perturbations technique and the study of the geodesic deviation. it is concluded that, generically, there is coincidence of the physical properties of the novel black holes in both frames, although this turns not to be the case for the hawking temperature. | spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in einstein's and jordan's frames |
thermodynamic stability of black holes, described by the rényi formula as equilibrium compatible entropy function, is investigated. it is shown that within this approach, asymptotically flat, schwarzschild black holes can be in stable equilibrium with thermal radiation at a fixed temperature. this implies that the canonical ensemble exists just like in anti-de sitter space, and nonextensive effects can stabilize the black holes in a very similar way as it is done by the gravitational potential of an anti-de sitter space. furthermore, it is also shown that a hawking-page-like black hole phase transition occurs at a critical temperature which depends on the q-parameter of the rényi formula. | rényi entropy and the thermodynamic stability of black holes |
in this work, we analyze the effects of thermal fluctuations on the thermodynamics of a modified hayward black hole. these thermal fluctuations will produce correction terms for various thermodynamical quantities like entropy, pressure, internal energy, and specific heats. we also investigate the effect of these correction terms on the first law of thermodynamics. finally, we study the phase transition for the modified hayward black hole. it is demonstrated that the modified hayward black hole is stable even after the thermal fluctuations are taken into account, as long as the event horizon is larger than a certain critical value. | effects of thermal fluctuations on the thermodynamics of modified hayward black hole |
we compute the exact retarded green's functions in thermal cfts with chemical potential and angular momenta using holography respectively. we consider the field equations satisfied by the quasi-normal modes in both charged and rotating black holes in ads spacetime and mapped them to the heun equations by appropriate changes of variables. the agt correspondence allows us to find the connection formulae among the solutions of the heun equations near different singularities by using the crossing relations of the five-point correlators in the liouville cft. the connection formulae associated with the boundary conditions imposed on the bulk field equations yield the exact thermal correlators in the boundary cft. | exact thermal correlators of holographic cfts |
banados, teitelboim, and zanelli (btz) black holes are excellent laboratories for studying black hole thermodynamics, which is a bridge between classical general relativity and the quantum nature of gravitation. in addition, three-dimensional gravity could have equipped us for exploring some of the ideas behind the two-dimensional conformal field theory based on the ads3/cft2 . considering the significant interest in these regards, we examine charged btz black holes. we consider the system contains massive gravity with energy dependent spacetime to enrich the results. in order to make high curvature (energy) btz black holes more realistic, we modify the theory by energy dependent constants. we investigate thermodynamic properties of the solutions by calculating heat capacity and free energy. we also analyze thermal stability and study the possibility of the hawking-page phase transition. at last, we study the geometrical thermodynamics of these black holes and compare the results of various approaches. | charged btz black holes in the context of massive gravity's rainbow |
primordial black holes in the mass range of ground-based gravitational-wave detectors can comprise a significant fraction of the dark matter. mass and spin measurements from coalescences can be used to distinguish between an astrophysical or a primordial origin of the binary black holes. in standard scenarios the spin of primordial black holes is very small at formation. however, the mass and spin can evolve through the cosmic history due to accretion. we show that the mass and spin of primordial black holes are correlated in a redshift-dependent fashion, in particular primordial black holes with masses below 𝒪(30)m· are likely non-spinning at any redshift, whereas heavier black holes can be nearly extremal up to redshift z~10. the dependence of the mass and spin distributions on the redshift can be probed with future detectors such as the einstein telescope. the mass and spin evolution affect the gravitational waveform parameters, in particular the distribution of the final mass and spin of the merger remnant, and that of the effective spin of the binary. we argue that, compared to the astrophysical-formation scenario, a primordial origin of black hole binaries might better explain the spin distribution of merger events detected by ligo-virgo, in which the effective spin parameter of the binary is compatible to zero except possibly for few high-mass events. upcoming results from ligo-virgo third observation run might reinforce or weaken these predictions. | the evolution of primordial black holes and their final observable spins |
the end state of hawking evaporation of a black hole is uncertain. some candidate quantum gravity theories, such as loop quantum gravity and asymptotic safe gravity, hint towards planck sized remnants. if so, the universe might be filled with remnants of tiny primordial black holes, which formed with mass $m\lt10^9$ g. a unique scenario is the case of $m\sim 5\times10^5$ g, where tiny primordial black holes reheat the universe by hawking evaporation and their remnants dominate the dark matter (dm). here, we point out that this scenario leads to a cosmological gravitational wave signal at frequencies ~100 hz. finding such a particular gravitational wave signature with, e.g. the einstein telescope, would suggest black hole remnants as dm. | gravitational wave hints black hole remnants as dark matter |
we consider the charged moments in sl(3, &r;) higher spin holography, as well as in the dual two-dimensional conformal field theory with w3 symmetry. for the vacuum state and a single entangling interval, we show that the w3 algebra of the conformal field theory induces an entanglement w3 algebra acting on the quantum state in the entangling interval. the algebra contains a spin 3 modular charge which commutes with the modular hamiltonian. the reduced density matrix is characterized by the modular energy and modular charge, hence our definition of the charged moments is also with respect to these conserved quantities. we evaluate the logarithm of the charged moments perturbatively in the spin 3 modular chemical potential, by computing the corresponding connected correlation functions of the modular charge operator up to quartic order in the chemical potential. this method provides access to the charged moments without using charged twist fields. our result matches known results for the charged moment obtained from the charged topological black hole picture in sl(3, &r;) higher spin gravity. since our charged moments are not gaussian in the chemical potential any longer, we conclude that the dual w3 conformal field theories must feature breakdown of equipartition of entanglement to leading order in the large c expansion. | charged moments in w3 higher spin holography |
binary black holes (bbhs) may form both through isolated binary evolution and through dynamical interactions in dense stellar environments. the formation channel leaves an imprint on the alignment between the bh spins and the orbital angular momentum. gravitational waves (gw) from these systems directly encode information about the spin-orbit misalignment angles, allowing them to be (weakly) constrained. identifying subpopulations of spinning bbhs will inform us about compact binary formation and evolution. we simulate a mixed population of bbhs with spin-orbit misalignments modelled under a range of assumptions. we then develop a hierarchical analysis and apply it to mock gw observations of these populations. assuming a population with dimensionless spin magnitudes of χ = 0.7, we show that tens of observations will make it possible to distinguish the presence of subpopulations of coalescing binary black holes based on their spin orientations. with 100 observations, it will be possible to infer the relative fraction of coalescing bbhs with isotropic spin directions (corresponding to dynamical formation in our models) with a fractional uncertainty of ∼40 per cent. meanwhile, only ∼5 observations are sufficient to distinguish between extreme models - all bbhs either having exactly aligned spins or isotropic spin directions. | hierarchical analysis of gravitational-wave measurements of binary black hole spin-orbit misalignments |
the nearby radio galaxy m87 offers a unique opportunity to explore the connections between the central supermassive black hole and relativistic jets. previous studies of the inner region of m87 revealed a wide opening angle for the jet originating near the black hole1-4. the event horizon telescope resolved the central radio source and found an asymmetric ring structure consistent with expectations from general relativity5. with a baseline of 17 years of observations, there was a shift in the jet's transverse position, possibly arising from an 8- to 10-year quasi-periodicity3. however, the origin of this sideways shift remains unclear. here we report an analysis of radio observations over 22 years that suggests a period of about 11 years for the variation in the position angle of the jet. we infer that we are seeing a spinning black hole that induces the lense-thirring precession of a misaligned accretion disk. similar jet precession may commonly occur in other active galactic nuclei but has been challenging to detect owing to the small magnitude and long period of the variation. | precessing jet nozzle connecting to a spinning black hole in m87 |
recently a consistent well-defined 4-dimensional einstein-gauss-bonnet theory of gravity was suggested in [k. aoki, m. gorji and s. mukohyama, phys. lett. b 810, 135843 (2020)]. while quasinormal modes of bosonic fields for this theory have been recently studied, there is no such study for fermionic fields. here we calculate quasinormal modes of the dirac field for spherically symmetric asymptotically flat black hole in this consistent 4 d einstein-gauss-bonnet theory. the values of the quasinormal frequencies, calculated by the sixth order wkb method with padé approximants and the time-domain integration, show that the real part of the quasinormal modes is considerably increased, while the damping rate is usually decreasing when the coupling constant is growing. | quasinormal modes of the dirac field in the consistent 4d einstein-gauss-bonnet gravity |
we consider the possibility that small black holes can act as nucleation seeds for the decay of a metastable vacuum, focussing particularly on the higgs potential. using a thin-wall bubble approximation for the nucleation process, which is possible when generic quantum gravity corrections are added to the higgs potential, we show that primordial black holes can stimulate vacuum decay. we demonstrate that for suitable parameter ranges, the vacuum decay process dominates over the hawking evaporation process. finally, we comment on the application of these results to vacuum decay seeded by black holes produced in particle collisions. | vacuum metastability with black holes |
recently, a non-local yet possibly uv-complete quantum field theory has been constructed by deforming a two-dimensional cft by the composite operator j\overline{t} , where j is a chiral u(1) current and \overline{t} is a component of the stress tensor. assuming the original cft was a holographic cft, we work out the holographic dual of its j\overline{t} deformation. we find that the dual spacetime is still ads3, but with modified boundary conditions that mix the metric and the chern-simons gauge field dual to the u(1) current. we show that when the coefficient of the chiral anomaly for j vanishes, the energy and thermodynamics of black holes obeying these modified boundary conditions precisely reproduce the previously derived field theory spectrum and thermodynamics. our proposed holographic dictionary can also reproduce the field-theoretical spectrum in presence of the chiral anomaly, upon a certain assumption that we justify. the asymptotic symmetry group associated to these boundary conditions consists of two copies of the virasoro and one copy of the u(1) kač-moody algebra, just as before the deformation; the only effect of the latter is to modify the spacetime dependence of the right-moving virasoro generators, whose action becomes state-dependent and effectively non-local. | the holographic interpretation of j\\overline{t} -deformed cfts |
we extend and refine a general method to extract the multipole moments of arbitrary stationary spacetimes and apply it to the study of a large family of regular horizonless solutions to n = 2 four-dimensional supergravity coupled to four abelian gauge fields. these microstate geometries can carry angular momentum and have a much richer multipolar structure than the kerr black hole. in particular they break the axial and equatorial symmetry, giving rise to a large number of nontrivial multipole moments. after studying some analytical examples, we explore the four-dimensional parameter space of this family with a statistical analysis. we find that microstate mass and spin multipole moments are typically (but not always) larger that those of a kerr black hole with the same mass and angular momentum. furthermore, we find numerical evidence that some invariants associated with the (dimensionless) moments of these microstates grow monotonically with the microstate size and display a global minimum at the black-hole limit, obtained when all centers collide. our analysis is relevant in the context of measurements of the multipole moments of dark compact objects with electromagnetic and gravitational-wave probes, and for observational tests to distinguish fuzzballs from classical black holes. | the multipolar structure of fuzzballs |
the black hole singularity plays a crucial role in formulating hawking's information paradox. the global spacetime analysis may be reconciled with unitarity by imposing a final state boundary condition on the spacelike singularity. motivated by the final state proposal, we explore the effect of final state projection in two dimensional conformal field theories. we calculate the time evolution under postselection by employing the real part of pseudoentropy to estimate the amount of quantum entanglement averaged over histories between the initial and final states. we find that this quantity possesses a page-curve-like behavior. | page curve under final state projection |
the type-ii weyl and type-ii dirac fermions may emerge behind the event horizon of black holes. correspondingly, the black hole can be simulated by creation of the region with overtilted weyl or dirac cones. the filling of the electronic states inside the "black hole" is accompanied by hawking radiation. the hawking temperature in the weyl semimetals can reach the room temperature, if the black hole region is sufficiently small, and thus the effective gravity at the horizon is large. | black hole and hawking radiation by type-ii weyl fermions |
we study quantum chaos of rotating btz black holes in topologically massive gravity (tmg). we discuss the relationship between chaos parameters including lyapunov exponents and butterfly velocities from shock wave calculations of out-of-time-order correlators (otoc) and from pole-skipping analysis. we find a partial match between pole-skipping and the otoc results in the high temperature regime. we also find that the velocity bound puts a chaos constraint on the gravitational chern-simons coupling. | quantum chaos in topologically massive gravity |
due to the failure of thermodynamics for low temperature near-extremal black holes, it has long been conjectured that a 'thermodynamic mass gap' exists between an extremal black hole and the lightest near-extremal state. for non-supersymmetric near-extremal black holes in einstein gravity with an ads 2 throat, no such gap was found. rather, at that energy scale, the spectrum exhibits a continuum of states, up to non-perturbative corrections. in this paper, we compute the partition function of near-bps black holes in supergravity where the emergent, broken, symmetry is psu(1, 1|2). to reliably compute this partition function, we show that the gravitational path integral can be reduced to that of a $\mathcal{n}=4$ supersymmetric extension of the schwarzian theory, which we define and exactly quantize. in contrast to the non-supersymmetric case, we find that black holes in supergravity have a mass gap and a large extremal black hole degeneracy consistent with the bekenstein-hawking area. our results verify a plethora of string theory conjectures, concerning the scale of the mass gap and the counting of extremal micro-states. | the statistical mechanics of near-bps black holes |
using "complexity=action" proposal we study complexity growth of certain gravitational theories containing higher derivative terms. these include critical gravity in diverse dimensions. one observes that the complexity growth for neutral black holes saturates the proposed bound when the results are written in terms of physical quantities of the model. we will also study effects of shock wave to the complexity growth where we find that the presence of massive spin-2 mode slows down the rate of growth. | on complexity for f ( r) and critical gravity |
quantum extremal surfaces (qes), codimension-2 spacelike regions which extremize the generalized entropy of a gravity-matter system, play a key role in the study of the black hole information problem. the thermodynamics of qess, however, has been largely unexplored, as a proper interpretation requires a detailed understanding of backreaction due to quantum fields. we investigate this problem in semi-classical jackiw-teitelboim (jt) gravity, where the spacetime is the eternal two-dimensional anti-de sitter (ads2) black hole, hawking radiation is described by a conformal field theory with central charge c, and backreaction effects may be analyzed exactly. we show the wald entropy of the semi-classical jt theory entirely encapsulates the generalized entropy — including time-dependent von neumann entropy contributions — whose extremization leads to a qes lying just outside of the black hole horizon. consequently, the qes defines a rindler wedge nested inside the enveloping black hole. we use covariant phase space techniques on a time-reflection symmetric slice to derive a smarr relation and first law of nested rindler wedge thermodynamics, regularized using local counterterms, and intrinsically including semi-classical effects. moreover, in the microcanonical ensemble the semi-classical first law implies the generalized entropy of the qes is stationary at fixed energy. thus, the thermodynamics of the nested rindler wedge is equivalent to the thermodynamics of the qes in the microcanonical ensemble. | semi-classical thermodynamics of quantum extremal surfaces in jackiw-teitelboim gravity |
in this paper, we study the dynamics of end-of-the-world (eow) branes in ads with scalar fields localized on the branes as a new class of gravity duals of cfts on manifolds with boundaries. this allows us to construct explicit solutions dual to boundary rg flows. we also obtain a variety of annulus-like or cone-like shaped eow branes, which are not possible without the scalar field. we also present a gravity dual of a cft on a strip with two different boundary conditions due to the scalar potential, where we find the confinement/deconfinement-like transition as a function of temperature and the scalar potential. finally, we point out that this phase transition is closely related to the measurement-induced phase transition, via a wick rotation. | ads/bcft with brane-localized scalar field |
we analytically calculate the influence of a plasma on the shadow of a black hole (or of another compact object). we restrict to spherically symmetric and static situations, where the shadow is circular. the plasma is assumed to be nonmagnetized and pressureless. we derive the general formulas for a spherically symmetric plasma density on an unspecified spherically symmetric and static spacetime. our main result is an analytical formula for the angular size of the shadow. as a plasma is a dispersive medium, the radius of the shadow depends on the photon frequency. the effect of the plasma is significant only in the radio regime. the formalism applies not only to black holes but also, e.g., to wormholes. as examples for the underlying spacetime model, we consider the schwarzschild spacetime and the ellis wormhole. in particular, we treat the case that the plasma is in radial free fall from infinity onto a schwarzschild black hole. we find that for an observer far away from a schwarzschild black hole, the plasma has a decreasing effect on the size of the shadow. the perspectives of actually observing the influence of a plasma on the shadows of supermassive black holes are discussed. | influence of a plasma on the shadow of a spherically symmetric black hole |
we present a systematic search for optical counterparts to 13 gravitational wave (gw) triggers involving at least one neutron star during ligo/virgo's third observing run (o3). we searched binary neutron star (bns) and neutron star black hole (nsbh) merger localizations with the zwicky transient facility (ztf) and undertook follow-up with the global relay of observatories watching transients happen (growth) collaboration. the gw triggers had a median localization area of 4480 deg2, a median distance of 267 mpc, and false-alarm rates ranging from 1.5 to 10-25 yr-1. the ztf coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. the o3 follow-up by the growth team comprised 340 ultraviolet/optical/infrared (uvoir) photometric points, 64 oir spectra, and three radio images using 17 different telescopes. we find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. initially, we assume that all gw triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying bns and nsbh mergers are drawn from a common population; later, we relax these assumptions. assuming that all kilonovae are at least as luminous as the discovery magnitude of gw170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. if we assume that all kilonovae are brighter than -16.6 mag (the extrapolated peak magnitude of gw170817) and fade at a rate of 1 mag day-1 (similar to gw170817), the joint probability of zero detections is 7%. if we separate the nsbh and bns populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than -16.6 mag, is 9.7% for nsbh and 7.9% for bns mergers. moreover, no more than <57% (<89%) of putative kilonovae could be brighter than -16.6 mag assuming flat evolution (fading by 1 mag day-1) at the 90% confidence level. if we further take into account the online terrestrial probability for each gw trigger, we find that no more than <68% of putative kilonovae could be brighter than -16.6 mag. comparing to model grids, we find that some kilonovae must have mej < 0.03 m⊙, xlan > 10-4, or φ > 30° to be consistent with our limits. we look forward to searches in the fourth gw observing run; even 17 neutron star mergers with only 50% coverage to a depth of -16 mag would constrain the maximum fraction of bright kilonovae to <25%. | kilonova luminosity function constraints based on zwicky transient facility searches for 13 neutron star merger triggers during o3 |
in holographic cfts satisfying eigenstate thermalization, there is a regime where the operator product expansion can be approximated by a random tensor network. the geometry of the tensor network corresponds to a spatial slice in the holographic dual, with the tensors discretizing the radial direction. in spherically symmetric states in any dimension and more general states in 2d cft, this leads to a holographic error-correcting code, defined in terms of ope data, that can be systematically corrected beyond the random tensor approximation. the code is shown to be isometric for light operators outside the horizon, and non-isometric inside, as expected from general arguments about bulk reconstruction. the transition at the horizon occurs due to a subtle breakdown of the virasoro identity block approximation in states with a complex interior. | toward random tensor networks and holographic codes in cft |
we utilize generalized unitarity and recursion relations combined with effective field theory techniques to compute spin-dependent interaction terms for an inspiralling binary system in the post-newtonian (pn) approximation. using these methods offers great computational advantage over traditional techniques involving feynman diagrams, especially at higher orders in the pn expansion. as a specific example, we reproduce the spin-orbit (up to 2.5pn order) and the leading-order s2 (2pn) hamiltonian for a binary system with one of the massive objects having nonzero spin using the s -matrix elements of elementary particles. for the same system, we also obtain the s3 (3.5pn) spin hamiltonian for an arbitrary massive object, which was until now known only for a black hole. furthermore, we derive the missing s4 hamiltonian at leading order (4pn), again for an arbitrary massive object and establish that the minimal coupling of an elementary particle to gravity automatically captures the physics of a spinning black hole. finally, the kerr metric is obtained as a series in gn by comparing the action of a test particle in the vicinity of a spinning black hole to the derived potential. | gravitational spin hamiltonians from the s matrix |
it was recently shown that the strong cosmic censorship conjecture might be violated for near-extremally-charged black holes in de sitter space. here, we extend our study to charged fermionic fields in the exterior of reissner-nordström-de sitter black holes. we identify three families of modes; one related to the photon sphere, a second related to the de sitter horizon and a third which dominates near extremality. we show that for near-extremally-charged black holes there is a critical fermionic charge below which strong cosmic censorship may potentially be violated. surprisingly enough, as one approaches extremality even more, violation of strong cosmic censorship may occur even beyond the critical fermionic charge. | charged fermions and strong cosmic censorship |
we consider the schwarzschild black hole and show how, in a theory with limiting curvature, the physical singularity "inside it" is removed. the resulting spacetime is geodesically complete. the internal structure of this nonsingular black hole is analogous to russian nesting dolls. namely, after falling into the black hole of radius rg, an observer, instead of being destroyed at the singularity, gets for a short time into the region with limiting curvature. after that he re-emerges in the near horizon region of a spacetime described by the schwarzschild metric of a gravitational radius proportional to rg^{1/3}. in the next cycle, after passing the limiting curvature, the observer finds himself within a black hole of even smaller radius proportional to rg^{1/9}, and so on. finally after a few cycles he will end up in the spacetime where he remains forever at limiting curvature. | nonsingular black hole |
the production rate of primordial black holes is often calculated by considering a nearly gaussian distribution of cosmological perturbations, and assuming that black holes will form in regions where the amplitude of such perturbations exceeds a certain threshold. a threshold $\zeta_{\rm th}$ for the curvature perturbation is somewhat inappropriate for this purpose, because it depends significantly on environmental effects, not essential to the local dynamics. by contrast, a threshold $\delta_{\rm th}$ for the density perturbation at horizon crossing seems to provide a more robust criterion. on the other hand, the density perturbation is known to be bounded above by a maximum limit $\delta_{\rm max}$, and given that $\delta_{\rm th}$ is comparable to $\delta_{\rm max}$, the density perturbation will be far from gaussian near or above the threshold. in this paper, we provide a new plausible estimate for the primordial black hole abundance based on peak theory. in our approach, we assume that the curvature perturbation is given as a random gaussian field with the power spectrum characterized by a single scale, while an optimized criterion for pbh formation is imposed, based on the locally averaged density perturbation. both variables are related by the full nonlinear expression derived in the long-wavelength approximation of general relativity. we do not introduce a window function, and the scale of the inhomogeneity is introduced as a random variable in the peak theory. we find that the mass spectrum is shifted to larger mass scales by one order of magnitude or so, compared to a conventional calculation. the abundance of pbhs becomes significantly larger than the conventional one, by many orders of magnitude, mainly due to the optimized criterion for pbh formation and the removal of the suppresion associated with a window function. | primordial black hole abundance from random gaussian curvature perturbations and a local density threshold |
the crossing equations of a conformal field theory can be systematically truncated to a finite, closed system of polynomial equations. in certain cases, solutions of the truncated equations place strict bounds on the space of all unitary cfts. we describe the conditions under which this holds, and use the results to develop a fast algorithm for modular bootstrap in 2d cft. we then apply it to compute spectral gaps to very high precision, find scaling dimensions for over a thousand operators, and extend the numerical bootstrap to the regime of large central charge, relevant to holography. this leads to new bounds on the spectrum of black holes in three-dimensional gravity. we provide numerical evidence that the asymptotic bound on the spectral gap from spinless modular bootstrap, at large central charge c, is δ1 ≲ c/9 .1. | fast conformal bootstrap and constraints on 3d gravity |
the zwicky transient facility (ztf) reported the event "ztf19abanrhr" as a candidate electromagnetic (em) counterpart at a redshift $z=0.438$ to the gravitational wave (gw) emission from the binary black hole merger gw190521. assuming that ztf19abanrhr is the {\it bona fide} em counterpart to gw190521, and using the gw luminosity distance estimate from three different waveforms nrsur7dq4, seobnrv4phm, and imrphenompv3hm, we report a measurement of the hubble constant $h_0= 50.4_{-19.5}^{+28.1}$ km/s/mpc, $ 62.2_{-19.7}^{+29.5}$ km/s/mpc, and $ 43.1_{-11.4}^{+24.6}$ km/s/mpc (median along with $68\%$ credible interval) respectively after marginalizing over matter density $\omega_m$ (or dark energy equation of state $w_0$) assuming the flat lcdm (or wcdm) model. combining our results with the binary neutron star event gw170817 with its redshift measurement alone, as well as with its inclination angle inferred from very large baseline interferometry (vlbi), we find $h_0= 67.6_{-4.2}^{+4.3}$ km/s/mpc, $\omega_m= 0.47_{-0.27}^{+0.34}$, and $w_0= -1.17_{-0.57}^{+0.68}$ (median along with $68\%$ credible interval) providing the most stringent measurement on $h_0$ and the first estimation on $\omega_m$ and $w_0$ from bright standard siren. in the future, $1.3\%$ measurement of $h_0=68$ km/s/mpc and $28\%$ measurement of $w_0=-1$ is possible from about $200$ gw190521-like sources. | first measurement of the hubble parameter from bright binary black hole gw190521 |
we study the physical properties of four-dimensional, string-theoretical, horizonless "fuzzball" geometries by imaging their shadows. their microstructure traps light rays straying near the would-be horizon on long-lived, highly redshifted chaotic orbits. in fuzzballs sufficiently near the scaling limit this creates a shadow much like that of a black hole, while avoiding the paradoxes associated with an event horizon. observations of the shadow size and residual glow can potentially discriminate between fuzzballs away from the scaling limit and alternative models of black compact objects. | fuzzball shadows: emergent horizons from microstructure |
recently, graham et al (2020 arxiv:2006.14122) identified ztf19abanrhr as a candidate electromagnetic counterpart to the binary black hole merger gw190521. the authors argue that the observations are consistent with a kicked binary black hole interacting with the accretion disk of the active galactic nucleus agn j124942.3 + 344929. if a real association (rather than happenstance), this has implications for the sources of ligo/virgo binary mergers, future prospects for electromagnetic counterparts, and measurements of the expansion rate of the universe. in this work, we provide an analysis of the multi-messenger coincident-significance based on the localisation overlap and find that, under optimistic assumptions, the odds of a common source for gw190521 and ztf19abanrhr range between 1 and 12. these odds are strongly dependent on the waveform model and, with current models, are unable to consistently capture both the effects of precession and orbital eccentricity. we consider this insufficient evidence to warrant confidently associating gw190521 with ztf19abanrhr and hence caution against any astrophysical conclusions based on the association. | current observations are insufficient to confidently associate the binary black hole merger gw190521 with agn j124942.3 + 344929 |
following up on a recent analysis by psaltis et al (2020 phys. rev. lett. 125 141104), we show that the observed shadow size of m87* can be used to unambiguously and robustly constrain the black hole geometry in the vicinity of the circular photon orbit. constraints on the post-newtonian weak-field expansion of the black hole's metric are instead more subtle to obtain and interpret, as they rely on combining the shadow-size measurement with suitable theoretical priors. we provide examples showing that post-newtonian constraints resulting from shadow-size measurements should be handled with extreme care. we also discuss the similarities and complementarity between the eht shadow measurements and black-hole gravitational quasi-normal modes. | eht tests of the strong-field regime of general relativity |
we study the spin of primordial black holes produced by the collapse of large inhomogeneities in the early universe. since such primordial black holes originate from peaks, that is, from maxima of the local overdensity, we resort to peak theory to obtain the probability distribution of the spin at formation. we show that the spin is a first-order effect in perturbation theory: it results from the action of first-order tidal gravitational fields generating first-order torques upon horizon-crossing, and from the asphericity of the collapsing object. assuming an ellipsoidal shape, the typical value of the dimensionless parameter as=s/gn m2, where s is the spin and m is the mass of the primordial black hole, is about (ωdm/π) σδ√1-γ2. here, σ2δ is the variance of the overdensity at horizon crossing, ωdm measures the current abundance of the dark matter and the parameter γ is a measure of the width of the power spectrum giving rise to primordial black holes. one has γ=1 for monochromatic spectra. for these narrow spectra, the suppression arises because the velocity shear, which is strongly correlated with the inertia tensor, tends to align with the principal axis frame of the collapsing object. typical values of as are at the percent level. | the initial spin probability distribution of primordial black holes |
axion stars, gravitationally bound states of low-energy axion particles, have a maximum mass allowed by gravitational stability. weakly bound states obtaining this maximum mass have sufficiently large radii such that they are dilute, and as a result, they are well described by a leading-order expansion of the axion potential. heavier states are susceptible to gravitational collapse. inclusion of higher-order interactions, present in the full potential, can give qualitatively different results in the analysis of collapsing heavy states, as compared to the leading-order expansion. in this work, we find that collapsing axion stars are stabilized by repulsive interactions present in the full potential, providing evidence that such objects do not form black holes. in the last moments of collapse, the binding energy of the axion star grows rapidly, and we provide evidence that a large amount of its energy is lost through rapid emission of relativistic axions. | collapse of axion stars |
we study charged black hole solutions in 4-dimensional (4d) einstein-gauss-bonnet-maxwell theory to the linearized perturbation level. we first compute the shear viscosity to entropy density ratio. we then demonstrate how bulk causal structure analysis imposes an upper bound on the gauss-bonnet coupling constant in the ads space. causality constrains the value of gauss-bonnet coupling constant αgb to be bounded by αgb≤0 as d →4. | causality of black holes in 4-dimensional einstein-gauss-bonnet-maxwell theory |
given two copies of any quantum mechanical system, one may want to prepare them in the thermofield double state for the purpose of studying thermal physics or black holes. however, the thermofield double is a unique entangled pure state and may be difficult to prepare. we propose a local interacting hamiltonian for the combined system whose ground state is approximately the thermofield double. the energy gap for this hamiltonian is of order the temperature. our construction works for any quantum system satisfying the eigenvalue thermalization hypothesis. | how to build the thermofield double state |
we consider the scattering of high energy and ultra relativistic spherically symmetric shells in asymptotically adsd spacetimes. we analyze an exclusive amplitude where a single spherically symmetric shell goes in and a single one comes out, such that the two have different global symmetry charges of the effective gravity theory. we study a simple wormhole configuration that computes the square of the amplitude and analyze its properties. | estimating global charge violating amplitudes from wormholes |
we perform the stability analysis on scalarized charged black holes in the einstein-maxwell-scalar (ems) theory by computing quasinormal mode spectrum. it is noted that the appearance of these black holes with scalar hair is closely related to the instability of reissner-nordström black holes without scalar hair in the ems theory. the scalarized charged black hole solutions are classified by the order number of n = 0 , 1 , 2 , ⋯, where n = 0 is called the fundamental branch and n = 1 , 2 , ⋯ denote the n excited branches. here, we show that the n = 1 , 2 excited black holes are unstable against the s (l = 0)-mode scalar perturbation, while the n = 0 black hole is stable against all scalar-vector-tensor perturbations. this is consistent with other scalarized black holes without charge found in the einstein-scalar-gauss-bonnet theory. | quasinormal modes of scalarized black holes in the einstein-maxwell-scalar theory |
we calculate the formation probability of primordial black holes generated during the collapse at horizon re-entry of large fluctuations produced during inflation, such as those ascribed to a period of ultra-slow-roll. we show that it interpolates between a gaussian at small values of the average density contrast and a cauchy probability distribution at large values. the corresponding abundance of primordial black holes may be larger than the gaussian one by several orders of magnitude. the mass function is also shifted towards larger masses. | the formation probability of primordial black holes |
with the recent release of the second gravitational wave transient catalog (gwtc-2), which introduced dozens of new detections, we are at a turning point of gravitational wave astronomy, as we are now able to directly infer constraints on the astrophysical population of compact objects. here, we tackle the burning issue of understanding the origin of binary black hole (bbh) mergers. to this effect, we make use of state-of-the-art population synthesis and n-body simulations, to represent two distinct formation channels: bbhs formed in the field (isolated channel) and in young star clusters (dynamical channel). we then use a bayesian hierarchical approach to infer the distribution of the mixing fraction f, with f = 0 (f = 1) in the pure dynamical (isolated) channel. we explore the effects of additional hyperparameters of the model, such as the spread in metallicity σz and the parameter σsp, describing the distribution of spin magnitudes. we find that the dynamical model is slightly favoured with a median value of f = 0.26, when σsp = 0.1 and σz = 0.4. models with higher spin magnitudes tend to strongly favour dynamically formed bbhs (f ≤ 0.1 if σsp = 0.3). furthermore, we show that hyperparameters controlling the rates of the model, such as σz, have a large impact on the inference of the mixing fraction, which rises from 0.18 to 0.43 when we increase σz from 0.2 to 0.6, for a fixed value of σsp = 0.1. finally, our current set of observations is better described by a combination of both formation channels, as a pure dynamical scenario is excluded at the $99{{\ \rm per\ cent}}$ credible interval, except when the spin magnitude is high. | new insights on binary black hole formation channels after gwtc-2: young star clusters versus isolated binaries |
we construct smooth static bubble solutions, denoted as topological stars, in five-dimensional einstein-maxwell theories which are asymptotic to &r;1,3×s1. the bubbles are supported by allowing electromagnetic fluxes to wrap smooth topological cycles. the solutions live in the same regime as non-extremal static charged black strings, that reduce to black holes in four dimensions. we generalize to multi-body configurations on a line by constructing closed-form generalized charged weyl solutions in the same theory. generic solutions consist of topological stars and black strings stacked on a line, that are wrapped by electromagnetic fluxes. we embed the solutions in type iib string theory on s1×t4. in this framework, the charged weyl solutions provide a novel class in string theory of multiple charged objects in the non-supersymmetric and non-extremal black hole regime. | topological stars, black holes and generalized charged weyl solutions |
by performing general relativistic hydrodynamics simulations with an approximate neutrino radiation transfer, the properties of ejecta in the dynamical and post-merger phases are investigated in the cases in which the remnant massive neutron star collapses into a black hole in ≲20 ms after the onset of the merger. the dynamical mass ejection is investigated in three-dimensional simulations. the post-merger mass ejection is investigated in two-dimensional axisymmetric simulations with viscosity using the three-dimensional post-merger systems as the initial conditions. we show that the typical neutron richness of the dynamical ejecta is higher for the merger of more asymmetric binaries; hence, heavier r-process nuclei are dominantly synthesized. the post-merger ejecta are shown to have only mild neutron richness, which results in the production of lighter r-process nuclei, irrespective of the binary mass ratios. because of the larger disk mass, the post-merger ejecta mass is larger for more asymmetric binary mergers. thus, the post-merger ejecta can compensate for the underproduced lighter r-process nuclei for asymmetric merger cases. as a result, by summing up both ejecta components, the solar residual r-process pattern is reproduced within the average deviation of a factor of three, irrespective of the binary mass ratio. our result also indicates that the (about a factor of a few) light-to-heavy abundance scatter observed in r-process-enhanced stars can be attributed to variation in the binary mass ratio and total mass. implications of our results associated with the mass distribution of compact neutron star binaries and the magnetar scenario of short gamma-ray bursts are discussed. | comprehensive study of mass ejection and nucleosynthesis in binary neutron star mergers leaving short-lived massive neutron stars |
we consider numerical black hole solutions in the weyl conformal geometry and its associated conformally invariant weyl quadratic gravity. in this model, einstein gravity (with a positive cosmological constant) is recovered in the spontaneously broken phase of weyl gravity after the weyl gauge field (ωμ) becomes massive through a stueckelberg mechanism and it decouples. as a first step in our investigations, we write down the conformally invariant gravitational action, containing a scalar degree of freedom and the weyl vector. the field equations are derived from the variational principle in the absence of matter. by adopting a static spherically symmetric geometry, the vacuum field equations for the gravitational, scalar, and weyl fields are obtained. after reformulating the field equations in a dimensionless form, and by introducing a suitable independent radial coordinate, we obtain their solutions numerically. we detect the formation of a black hole from the presence of a killing horizon for the timelike killing vector in the metric tensor components, indicating the existence of the singularity in the metric. several models corresponding to different functional forms of the weyl vector are considered. an exact black hole model corresponding to a weyl vector having only a radial spacelike component is also obtained. the thermodynamic properties of the weyl geometric type black holes (horizon temperature, specific heat, entropy, and evaporation time due to hawking luminosity) are also analyzed in detail. | black hole solutions in the quadratic weyl conformal geometric theory of gravity |
we present the black hole accretion code ( bhac), a new multidimensional general-relativistic magnetohydrodynamics module for the mpi-amrvac framework. bhac has been designed to solve the equations of ideal general-relativistic magnetohydrodynamics in arbitrary spacetimes and exploits adaptive mesh refinement techniques with an efficient block-based approach. several spacetimes have already been implemented and tested. we demonstrate the validity of bhac by means of various one-, two-, and three-dimensional test problems, as well as through a close comparison with the harm3d code in the case of a torus accreting onto a black hole. the convergence of a turbulent accretion scenario is investigated with several diagnostics and we find accretion rates and horizon-penetrating fluxes to be convergent to within a few percent when the problem is run in three dimensions. our analysis also involves the study of the corresponding thermal synchrotron emission, which is performed by means of a new general-relativistic radiative transfer code, bhoss. the resulting synthetic intensity maps of accretion onto black holes are found to be convergent with increasing resolution and are anticipated to play a crucial role in the interpretation of horizon-scale images resulting from upcoming radio observations of the source at the galactic center. | the black hole accretion code |
the discoveries of gw150914, gw151226, and lvt151012 suggest that double black hole (bh-bh) mergers are common in the universe. if at least one of the two merging black holes (bhs) carries a certain amount of charge, possibly retained by a rotating magnetosphere, the inspiral of a bh-bh system would drive a global magnetic dipole normal to the orbital plane. the rapidly evolving magnetic moment during the merging process would drive a poynting flux with an increasing wind power. the magnetospheric activities during the final phase of the merger would make a fast radio burst (frb) if the bh charge can be as large as a factor of \hat{q}∼ ({10}-9{--}{10}-8) of the critical charge qcof the bh. at large radii, dissipation of the poynting flux energy in the outflow would power a short-duration high-energy transient, which would appear as a detectable short-duration gamma-ray burst (grb) if the charge can be as large as \hat{q}∼ ({10}-5{--}{10}-4). the putative short grb coincident with gw150914 recorded by fermi gbm may be interpreted with this model. future joint gw/grb/frb searches would lead to a measurement or place a constraint on the charges carried by isolate bhs. | mergers of charged black holes: gravitational-wave events, short gamma-ray bursts, and fast radio bursts |
there is irresistible observational evidence that binary systems of compact objects with at least one neutron star are progenitors of short gamma-ray bursts, as well as a production site for r -process elements, at least when some matter is ejected by the merger and an accretion disk is formed. the recent observations of gravitational waves in conjunction with electromagnetic counterparts fuel the need for models predicting the outcome of a given merger and the properties of the associated matter outflows as a function of the initial parameters of the binary. in this manuscript, we provide updated fitting formulas that estimate the disk mass for double neutron star binaries and ejecta masses for black hole-neutron star and double neutron star binaries, fitted to the results of numerical simulations. our proposed fitting formulas improve on existing models by aiming for analytical simplicity, by covering a larger region of parameter space, and by accounting for regions of parameter space not covered by numerical simulations but with physically manifest merger outcomes. | estimates for disk and ejecta masses produced in compact binary mergers |
we study a mechanism for the amplification of the inflationary scalar perturbation when the inflaton field action is non-canonical, i.e. the inflaton kinetic term has a non-standard form. for such a case the speed of sound of the perturbations generated during inflation is less than one and in general changes with time. furthermore in such models, even when the scalar field potential is negligible, diverse inflationary attractors may exist. the possible effects of a speed of sound approaching zero during some stage of inflation may lead to a large amplification for the amplitude of the scalar spectrum which, on horizon re-entry during the radiation dominated phase, can collapse and form primordial black holes (pbh) of a mass mbh ∼10-15m⊙ which may constitute a large fraction of the total dark matter (dm) today. | non-canonical inflation and primordial black holes production |
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