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despite the absence of a lightcone structure, some solutions of carroll gravity show black hole-like behaviour. we define carroll black holes as solutions of carroll gravity that exhibit carroll thermal properties and have a carroll extremal surface, notions introduced in our work. the latter is a carroll analogue of a lorentzian extremal surface. as examples, we discuss the carroll versions of schwarzschild, reissner-nordström, and btz black holes and black hole solutions of generic 1+1 dimensional carroll dilaton gravity, including carroll jt and carroll witten black holes. | carroll black holes |
we study the evaporation of two-dimensional black holes in jt gravity from a three-dimensional point of view. a partial dimensional reduction of ads3 in poincaré coordinates leads to an extremal 2d black hole in jt gravity coupled to a `bath': the holographic dual of the remainder of the 3d spacetime. partially reducing the btz black hole gives us the finite temperature version. we compute the entropy of the radiation using geodesics in the three-dimensional spacetime. we then focus on the finite temperature case and describe the dynamics by introducing time-dependence into the parameter controlling the reduction. the energy of the black hole decreases linearly as we slowly move the dividing line between black hole and bath. through a re-scaling of the btz parameters we map this to the more canonical picture of exponential evaporation. finally, studying the entropy of the radiation over time leads to a geometric representation of the page curve. the appearance of the island region is explained in a natural and intuitive fashion. | from the btz black hole to jt gravity: geometrizing the island |
most massive stars are members of a binary or a higher-order stellar system, where the presence of a binary companion can decisively alter their evolution via binary interactions. interacting binaries are also important astrophysical laboratories for the study of compact objects. binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. here, we present posydon, a novel, publicly available, binary population synthesis code that incorporates full stellar structure and binary-evolution modeling, using the mesa code, throughout the whole evolution of the binaries. the use of posydon enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates, and orbital periods. this paper describes the detailed methodology and implementation of posydon, including the assumed physics of stellar and binary evolution, the extensive grids of detailed single- and binary-star models, the postprocessing, classification, and interpolation methods we developed for use with the grids, and the treatment of evolutionary phases that are not based on precalculated grids. the first version of posydon targets binaries with massive primary stars (potential progenitors of neutron stars or black holes) at solar metallicity. | posydon: a general-purpose population synthesis code with detailed binary-evolution simulations |
we present the construction of several microstate geometries of the supersymmetric d1-d5-p black hole in which, within six-dimensional supergravity, the momentum charge is carried by a vector field. the fully backreacted geometries are smooth and horizonless: they are asymptotically ads3 × s3 with an ads2 throat that smoothly caps off. we propose a holographic dual for these bulk solutions and discuss their extension to asymptotically flat space. in addition, we present several uplifts of the full six-dimensional supersymmetric ansatz to ten-dimensions. in particular, we show that there exists a frame in which geometries based on vector field momentum carriers are entirely in the ns-ns sector, making them possible starting points for the exploration of stringy black-hole microstates. | vector superstrata |
in this paper, utilizing the generalized off shell helmholtz free energy, we explore the topological numbers of the four-dimensional static accelerating black hole and its ads extension, as well as the static charged accelerating black hole and its ads extension. our analysis reveals a profound and significant impact of the acceleration parameter on the topological numbers associated with the static black holes; and different values (nonzero) of the acceleration parameter do not affect the topological numbers of the corresponding four-dimensional static accelerating black holes. in addition, we demonstrate that the electric charge parameter has an important effect on the topological number of the static neutral accelerating black holes, and the cosmological constant has a remarkable influence on the topological number of the static accelerating black hole. furthermore, it is interesting to observe that the difference between the topological number of the asymptotically flat static accelerating black hole and that of its corresponding asymptotically flat static nonaccelerating black hole is always unity, and the difference between the topological number of the asymptotically ads static accelerating black hole and that of its corresponding asymptotically ads static nonaccelerating black hole is always -1 . this new observation leads us to conjure that it might be valid also for other accelerating black holes. of course, this captivating conjecture requires empirical verification through comprehensive investigation into the topological numbers of other accelerating black holes and their corresponding usual counterparts. | topological classes of thermodynamics of the four-dimensional static accelerating black holes |
the joule-thomson expansion process is studied for charged gauss-bonnet black holes in ads space. first, in five-dimensional space-time, the isenthalpic curve in t -p graph is obtained and the cooling-heating region is determined. second, the explicit expression of joule-thomson coefficient is obtained from the basic formulas of enthalpy and temperature. our methods can also be applied to van der waals system as well as other black hole systems. and the inversion curve t ∼(p ∼) which separates the cooling region and heating region is obtained and investigated. third, interesting dependence of the inversion curves on the charge (q ) and the gauss-bonnet parameter (α ) is revealed. in t ∼-p ∼ graph, the cooling region decreases with charge, but increases with the gauss-bonnet parameter. fourth, by applying our methods, the joule-thomson expansion process for α =0 case in four dimension is studied, where the gauss-bonnet ads black hole degenerates into rn-ads black hole. the inversion curves for van der waals systems consist of two parts. one has positive slope, while the other has negative slope. however, for black hole systems, the slopes of the inversion curves are always positive, which seems to be a universal feature. | joule-thomson expansion of charged gauss-bonnet black holes in ads space |
we propose that the fracton models with subsystem symmetry can be a class of toy models for the holographic principle. the discovery of the anti-de sitter/conformal field theory correspondence as a concrete construction of holography and the subsequent developments including the subregion duality and ryu-takayanagi formula of entanglement entropy have revolutionized our understanding of quantum gravity and provided powerful tool sets for solving various strongly coupled quantum field theory problems. to resolve many mysteries of holography, toy models can be very helpful. one example is the holographic tensor networks, which illuminate the quantum-error-correcting properties of gravity in the anti-de sitter space. in this work we discuss a classical toy model featuring subsystem symmetries and immobile fracton excitations. we show that such a model defined on the hyperbolic lattice satisfies some key properties of the holographic correspondence. the correct subregion duality and ryu-takayanagi formula for mutual information are established for a connected boundary region. a naively defined black hole's entropy scales as its horizon area. we also present discussions on corrections for more complicated boundary subregions, the possible generalizations of the model, and a comparison with the holographic tensor networks. | hyperbolic fracton model, subsystem symmetry, and holography |
black hole and neutron star x-ray binary systems routinely show quasi-periodic oscillations (qpos) in their x-ray flux. despite being strong, easily measurable signals, their physical origin has long remained elusive. however, recent observational and theoretical work has greatly improved our understanding. here, we briefly review the basic phenomenology of the different varieties of qpo in both black hole and neutron star systems before focusing mainly on low frequency qpos in black hole systems, for which much of the recent progress has been made. we describe the detailed statistical properties of these qpos and review the physical models proposed in the literature, with particular attention to those based on lense-thirring precession. this is a relativistic effect whereby a spinning massive object twists up the surrounding spacetime, inducing nodal precession in inclined orbits. we review the theory describing how an accretion flow reacts to the lense-thirring effect, including analytic theory and recent numerical simulations. we then describe recent observational tests that provide very strong evidence that at least a certain type of low frequency qpos are a geometric effect, and good evidence that they are the result of precession. we discuss the possibility of the spin axis of the compact object being misaligned with the binary rotation axis for a large fraction of x-ray binaries, as is required for qpos to be driven specifically by lense-thirring precession, as well as some outstanding gaps in our understanding and future opportunities provided by x-ray polarimeters and/or high throughput x-ray detectors. | a review of quasi-periodic oscillations from black hole x-ray binaries: observation and theory |
bms symmetry, which is the asymptotic symmetry at null infinity of flat spacetime, is an important input for flat holography. in this paper, we give a holographic calculation of entanglement entropy and rényi entropy in three dimensional einstein gravity and topologically massive gravity. the geometric picture for the entanglement entropy is the length of a spacelike geodesic which is connected to the interval at null infinity by two null geodesics. the spacelike geodesic is the fixed points of replica symmetry, and the null geodesics are along the modular flow. our strategy is to first reformulate the rindler method for calculating entanglement entropy in a general setup, and apply it for bms invariant field theories, and finally extend the calculation to the bulk. | entanglement entropy in flat holography |
we find that collisions of near-horizon-sized bubbles with a thick fluid shell can produce primordial black holes (pbhs) during a first-order phase transition. we predict an approximately monochromatic pbh mass spectrum. in terms of a few parameters to be obtained from future numerical simulation, we estimate the pbh abundance in an abelian higgs benchmark model and show that it can be significant. in particular, the pbhs can constitute entire dark matter or even over-close the universe. our result thus shows that models with a first-order phase transition can be constrained by over-abundant pbhs or null results of other pbh searches. | primordial black holes from bubble collisions during a first-order phase transition |
we give a brief review on the formation and the calculation of black hole shadows. firstly, we introduce the concept of a black hole shadow and the current works on a variety of black hole shadows. secondly, we present the main methods of calculating photon sphere radius and shadow radius, and then explain how the photon sphere affects the boundary of black hole shadows. we review the analytical calculation for black hole shadows which have analytic expressions for shadow boundary due to the integrable photon motion system. and we introduce the fundamental photon orbits which can explain the patterns of black hole shadow shape. finally, we review the numerical calculation of black hole shadows with the backward ray-tracing method and introduce some chaotic black hole shadows with self-similar fractal structures. since the gravitational waves from the merger of binary black holes have been detected, we introduce a couple of shadows of binary black holes, which all have eyebrowlike shadows around the main shadows with the fractal structures. we discuss the invariant phase space structures of the photon motion system in black hole space-time, and explain the formation of black hole shadow is dominated by the invariant manifolds of certain lyapunov orbits near the fixed points. | chaotic shadows of black holes: a short review |
models in which dark matter consists entirely of primordial black holes (pbhs) with masses around 1 017 g are currently unconstrained. however, if pbhs are a component of the galactic dark matter density, they will inject a large flux of energetic particles into the galaxy as they radiate. positrons produced by these black holes will subsequently propagate throughout the galaxy and annihilate, contributing to the galactic 511 kev line. using measurements of this line by the integral satellite as a constraint on pbh positron injection, we place new limits on pbh abundance in the mass range 1 016- 1 017 g , ruling out models in which these pbhs constitute the entirety of dark matter. | constraining primordial black hole abundance with the galactic 511 kev line |
the shadows cast by non-rotating and rotating modified gravity black holes are determined by the two parameters mass and angular momentum . the sizes of the shadows cast by the spherically symmetric static modified gravity-schwarzschild and modified gravity-kerr rotating black holes increase significantly as the free parameter is increased from zero. the event horizon telescope shadow image measurements can determine whether einstein's general relativity is correct or whether it should be modified in the presence of strong gravitational fields. | modified gravity black holes and their observable shadows |
observable thermodynamical properties of the intracluster medium (icm) reflect the complex interplay between agn feedback and the gravitational collapse of haloes. using the large volume tng300 simulation of the illustristng project we provide predictions for x-ray and sunyaev-zel'dovich (sz) scaling relations for a sample of over 30,000 haloes that cover a wide mass range from galaxies to massive galaxy clusters ($m_{\rm 500crit}$ $\in [10^{12}$ m$_{\odot} - 2\times 10^{15}$ m$_{\odot}$]). we produce mock x-ray observations of simulated haloes using methods that are consistent with observational techniques. thus, we investigate the scaling relations between the soft-band x-ray luminosity, spectroscopic temperature, gas mass fraction, $y_{\rm x}$ and $y_{\rm sz}$ as a function of halo mass, and we find broad agreement between illustristng and the observed relations. our results highlight the scatter and bias introduced by estimated masses, and thus the importance of converting simulated icm properties to the observable space when comparing simulations to current x-ray observations. the wide range of halo masses in our sample provides new insights into the shape of the x-ray and sz scaling relations across three orders of magnitude in mass. our findings show strong evidence for a break in $z=0$ scaling relations. we introduce a smoothly broken power law model which robustly captures the location of this break, the width of the transition region around the break, as well as the slope dependence on halo mass. our results inform the next generation of subgrid black hole feedback models and provide predictions for ongoing and future observational surveys. | sunyaev-zel'dovich effect and x-ray scaling relations of galaxies, groups and clusters in the illustristng simulations |
we introduce the use of autoregressive normalizing flows for rapid likelihood-free inference of binary black hole system parameters from gravitational-wave data with deep neural networks. a normalizing flow is an invertible mapping on a sample space that can be used to induce a transformation from a simple probability distribution to a more complex one: if the simple distribution can be rapidly sampled and its density evaluated, then so can the complex distribution. our first application to gravitational waves uses an autoregressive flow, conditioned on detector strain data, to map a multivariate standard normal distribution into the posterior distribution over system parameters. we train the model on artificial strain data using a model for the gravitational-wave signal that includes inspiral, merger and ringdown and draw waveforms from a five-parameter (m1,m2,ϕ0,tc,dl) prior and stationary gaussian noise realizations with a fixed power spectral density. this gives performance comparable to current best deep-learning approaches to gravitational-wave parameter estimation. we then build a more powerful latent variable model by incorporating autoregressive flows within the variational autoencoder framework. this model has performance comparable to markov chain monte carlo and, in particular, successfully models the multimodal ϕ0 posterior. finally, we train the autoregressive latent variable model on an expanded parameter space, including also aligned spins (χ1 z,χ2 z) and binary inclination θj n, and show that all parameters and degeneracies and most uncertainties are well-recovered. in all cases, sampling is extremely fast, requiring less than two seconds to draw 104 posterior samples. | gravitational-wave parameter estimation with autoregressive neural network flows |
we argue that a remnant is formed for all black objects in gravity's rainbow. this will be based on the observation that a remnant depends critically on the structure of the rainbow functions, and this dependence is a model independent phenomena. we thus propose general relations for the modified temperature and entropy of all black objects in gravity's rainbow. we explicitly check this to be the case for kerr, kerr-newman-ds, charged-ads, and higher dimensional kerr-ads black holes. we also try to argue that a remnant should form for black saturn in gravity's rainbow. this work extends our previous results on remnants of schwarzschild black holes [1] and black rings [2]. | remnant for all black objects due to gravity's rainbow |
as the only non-carbon elemental layered allotrope, few-layer black phosphorus or phosphorene has emerged as a novel two-dimensional (2d) semiconductor with both high bulk mobility and a band gap. here we report fabrication and transport measurements of phosphorene-hexagonal bn (hbn) heterostructures with one-dimensional edge contacts. these transistors are stable in ambient conditions for >300 h, and display ambipolar behavior, a gate-dependent metal-insulator transition, and mobility up to 4000 cm2 v-1 s-1. at low temperatures, we observe gate-tunable shubnikov de haas magneto-oscillations and zeeman splitting in magnetic field with an estimated g-factor ∼2. the cyclotron mass of few-layer phosphorene (flp) holes is determined to increase from 0.25 to 0.31 me as the fermi level moves towards the valence band edge. our results underscore the potential of flp as both a platform for novel 2d physics and an electronic material for semiconductor applications. | gate tunable quantum oscillations in air-stable and high mobility few-layer phosphorene heterostructures |
charged black holes in anti-de sitter space become unstable to forming charged scalar hair at low temperatures t < t_\text{c}t<tc. this phenomenon is a holographic realization of superconductivity. we look inside the horizon of these holographic superconductors and find intricate dynamical behavior. the spacetime ends at a spacelike kasner singularity, and there is no cauchy horizon. before reaching the singularity, there are several intermediate regimes which we study both analytically and numerically. these include strong josephson oscillations in the condensate and possible `kasner inversions' in which after many e-folds of expansion, the einstein-rosen bridge contracts towards the singularity. due to the josephson oscillations, the number of kasner inversions depends very sensitively on tt, and diverges at a discrete set of temperatures \{t_n\}{tn} that accumulate at t_ctc. near these t_ntn, the final kasner exponent exhibits fractal-like behavior. | diving into a holographic superconductor |
a dark matter overdensity around a black hole may significantly alter the dynamics of the black hole's merger with another compact object. we consider here intermediate mass-ratio inspirals of stellar-mass compact objects with intermediate-mass black holes "dressed" with dark matter. we first demonstrate that previous estimates based on a fixed dark-matter dress are unphysical for a range of binaries and dark-matter distributions by showing that the total energy dissipated by the compact object through dynamical friction, as it inspirals through the dense dark matter environment toward the black hole, is larger than the gravitational binding energy of the dark-matter dress itself. we then introduce a new formalism that allows us to self-consistently follow the evolution of the dark-matter dress due to its gravitational interaction with the binary. we show that the dephasing of the gravitational waveform induced by dark matter is smaller than previously thought, but is still potentially detectable with the lisa space interferometer. the gravitational waves from such binaries could provide powerful diagnostics of the particle nature of dark matter. | detecting dark matter around black holes with gravitational waves: effects of dark-matter dynamics on the gravitational waveform |
the weak gravity conjecture (wgc) demands the existence of superextremal particles in any consistent quantum theory of gravity. the standard lore is that these particles are introduced to ensure that extremal black holes are either unstable or marginally stable, but it is not clear what is wrong if this doesn't happen. this note shows that, for a generic einstein quantum theory of gravity in ads, exactly stability of extremal black branes is in tension with rigorously proven quantum information theorems about entanglement entropy. avoiding the contradiction leads to a nonperturbative version of the wgc, which reduces to the usual statement at weak coupling. the argument is general, and it does not rely on either supersymmetry or a particular uv completion, assuming only the validity of einsteinian gravity, effective field theory, and holography. the pathology is related to the development of an infinite throat in the near-horizon region of the extremal solutions, which suggests a connection to the er=epr proposal. | a holographic derivation of the weak gravity conjecture |
einstein-maxwell-scalar models allow for different classes of black hole solutions, depending on the non-minimal coupling function f (ϕ ) employed, between the scalar field and the maxwell invariant. here, we address the linear mode stability of the black hole solutions obtained recently for a quartic coupling function, f (ϕ ) =1 +α ϕ4 (blázquez-salcedo et al. in phys. lett. b 806:135493, 2020). besides the bald reissner-nordström solutions, this coupling allows for two branches of scalarized black holes, termed cold and hot, respectively. for these three branches of black holes we calculate the spectrum of quasinormal modes. it consists of polar scalar-led modes, polar and axial electromagnetic-led modes, and polar and axial gravitational-led modes. we demonstrate that the only unstable mode present is the radial scalar-led mode of the cold branch. consequently, the bald reissner-nordström branch and the hot scalarized branch are both mode-stable. the non-trivial scalar field in the scalarized background solutions leads to the breaking of the degeneracy between axial and polar modes present for reissner-nordström solutions. this isospectrality is only slightly broken on the cold branch, but it is strongly broken on the hot branch. | quasinormal modes of hot, cold and bald einstein-maxwell-scalar black holes |
we compare the set of local galaxies having dynamically measured black holes with a large, unbiased sample of galaxies extracted from the sloan digital sky survey. we confirm earlier work showing that the majority of black hole hosts have significantly higher velocity dispersions σ than local galaxies of similar stellar mass. we use monte carlo simulations to illustrate the effect on black hole scaling relations if this bias arises from the requirement that the black hole sphere of influence must be resolved to measure black hole masses with spatially resolved kinematics. we find that this selection effect artificially increases the normalization of the mbh-σ relation by a factor of at least ∼3; the bias for the mbh-mstar relation is even larger. our monte carlo simulations and analysis of the residuals from scaling relations both indicate that σ is more fundamental than mstar or effective radius. in particular, the mbh-mstar relation is mostly a consequence of the mbh-σ and σ-mstar relations, and is heavily biased by up to a factor of 50 at small masses. this helps resolve the discrepancy between dynamically based black hole-galaxy scaling relations versus those of active galaxies. our simulations also disfavour broad distributions of black hole masses at fixed σ. correcting for this bias suggests that the calibration factor used to estimate black hole masses in active galaxies should be reduced to values of fvir ∼ 1. black hole mass densities should also be proportionally smaller, perhaps implying significantly higher radiative efficiencies/black hole spins. reducing black hole masses also reduces the gravitational wave signal expected from black hole mergers. | selection bias in dynamically measured supermassive black hole samples: its consequences and the quest for the most fundamental relation |
the compact and, with {∼ }4.3± 0.3× 10^6 m_{\odot }, very massive object located at the center of the milky way is currently the very best candidate for a supermassive black hole (smbh) in our immediate vicinity. the strongest evidence for this is provided by measurements of stellar orbits, variable x-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source sagittarius a* (sgra*) in the middle of the central stellar cluster. simultaneous near-infrared and x-ray observations of sgra* have revealed insights into the emission mechanisms responsible for the powerful near-infrared and x-ray flares from within a few tens to one hundred schwarzschild radii of such a putative smbh. if sgra* is indeed a smbh it will, in projection onto the sky, have the largest event horizon and will certainly be the first and most important target for very long baseline interferometry observations currently being prepared by the event horizon telescope (eht). these observations in combination with the infrared interferometry experiment gravity at the very large telescope interferometer and other experiments across the electromagnetic spectrum might yield proof for the presence of a black hole at the center of the milky way. the large body of evidence continues to discriminate the identification of sgra* as a smbh from alternative possibilities. it is, however, unclear when the ever mounting evidence for sgra* being associated with a smbh will suffice as a convincing proof. additional compelling evidence may come from future gravitational wave observatories. this manuscript reviews the observational facts, theoretical grounds and conceptual aspects for the case of sgra* being a black hole. we treat theory and observations in the framework of the philosophical discussions about "(anti)realism and underdetermination", as this line of arguments allows us to describe the situation in observational astrophysics with respect to supermassive black holes. questions concerning the existence of supermassive black holes and in particular sgra* are discussed using causation as an indispensable element. we show that the results of our investigation are convincingly mapped out by this combination of concepts. | the milky way's supermassive black hole: how good a case is it? |
we propose a new way of probing the nonthermal origin of baryon asymmetry of the universe (bau) and dark matter (dm) from evaporating primordial black holes (pbhs) via stochastic gravitational waves (gws) emitted due to pbh density fluctuations. we adopt a baryogenesis setup where c p -violating out-of-equilibrium decays of a colored scalar, produced nonthermally at late epochs from pbh evaporation, lead to the generation of bau. the same pbh evaporation is also responsible for nonthermal origin of superheavy dm. unlike the case of baryogenesis via leptogenesis that necessarily corners the pbh mass to ∼o (1 ) g , here we can have pbh mass as large as ∼o (107) g due to the possibility of producing bau directly below sphaleron decoupling temperature. because of the larger allowed pbh mass we can also have observable gw with mhz-khz frequencies originating from pbh density fluctuations keeping the model constrained and verifiable at ongoing as well as near future gw experiments like ligo, bbo, decigo, ce, et etc. because of the presence of new colored particles and baryon number violation, the model also has complementary detection prospects at laboratory experiments. | gravitational wave signatures of a pbh-generated baryon-dark matter coincidence |
we model the broad-band (optical/uv and x-ray) continuum spectrum of the `changing-look' active galactic nucleus (agn) mrk 1018, as it fades from seyfert 1 to 1.9 in ∼ 8 years. the brightest spectrum, with eddington ratio l/ledd ∼ 0.08 has a typical type 1 agn continuum, with a strong `soft x-ray excess' spanning between the uv and soft x-rays. the dimmest spectrum, at l/ledd ∼ 0.006, is very different in shape as well as luminosity, with the soft excess dropping by much more than the hard x-rays. the soft x-ray excess produces most of the ionizing photons, so its dramatic drop leads to the disappearance of the broad-line region, driving the `changing-look' phenomena. this spectral hardening appears similar to the soft-to-hard state transition in black hole binaries at l/ledd ∼ 0.02, where the inner disc evaporates into an advection dominated accretion flow, while the overall drop in luminosity appears consistent with the hydrogen ionization disc instability. none the less, both processes happen much faster in mrk 1018 than predicted by disc theory. we critically examine scaling from galactic binary systems and show that a major difference is that radiation pressure should be much more important in agns, so that the sound speed is much faster than expected from the gas temperature. including magnetic pressure to stabilize the disc shortens the time-scales even further. we suggest that all changing-look agns are similarly associated with the state transition at l/ledd ∼ a few per cent. | explaining changing-look agn with state transition triggered by rapid mass accretion rate drop |
scrambling of quantum information is an important feature at the root of randomization and benchmarking protocols, the onset of quantum chaos, and black-hole physics. unscrambling this information is possible given perfect knowledge of the scrambler[arxiv:1710.03363]. we show that one can retrieve the scrambled information even without any previous knowledge of the scrambler, by a learning algorithm that allows the building of an efficient decoder. remarkably, the decoder is classical in the sense that it can be efficiently represented on a classical computer as a clifford operator. it is striking that a classical decoder can retrieve with fidelity one all the information scrambled by a random unitary that {\em cannot} be efficiently simulated on a classical computer, as long as there is no full-fledged quantum chaos. this result shows that one can learn the salient properties of quantum unitaries in a classical form, and sheds a new light on the meaning of quantum chaos. furthermore, we obtain novel results concerning the algebraic structure of $t$-doped clifford circuits, i.e. clifford circuits containing t non-clifford gates, their gate complexity, and learnability that are of independent interest. in particular, we show that a $t$-doped clifford circuit has gate complexity $\mathcal{o}(n^2\log^{-1}n+t^3\log^{-1}t)$ and can be learned with $\mathcal{o}(poly(n)\exp(t))$ resources. | learning efficient decoders for quasi-chaotic quantum scramblers |
we present a search for subsolar mass ultracompact objects in data obtained during advanced ligo's second observing run. in contrast to a previous search of advanced ligo data from the first observing run, this search includes the effects of component spin on the gravitational waveform. we identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between 0.2 m⊙- 1.0 m⊙ . we use the null result to constrain the binary merger rate of (0.2 m⊙ , 0.2 m⊙ ) binaries to be less than 3.7 ×105 gpc-3 yr-1 and the binary merger rate of (1.0 m⊙ , 1.0 m⊙ ) binaries to be less than 5.2 ×103 gpc-3 yr-1 . subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. assuming a particular primordial black hole (pbh) formation model, we constrain a population of merging 0.2 m⊙ black holes to account for less than 16% of the dark matter density and a population of merging 1.0 m⊙ black holes to account for less than 2% of the dark matter density. we discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries. | search for subsolar mass ultracompact binaries in advanced ligo's second observing run |
we consider the following question: may two different black holes (bhs) cast exactly the same shadow? in spherical symmetry, we show the necessary and sufficient condition for a static bh to be shadow-degenerate with schwarzschild is that the dominant photonsphere of both has the same impact parameter, when corrected for the (potentially) different redshift of comparable observers in the different spacetimes. such shadow-degenerate geometries are classified into two classes. the first shadow-equivalent class contains metrics whose constant (areal) radius hypersurfaces are isometric to those of the schwarzschild geometry, which is illustrated by the simpson and visser (sv) metric. the second shadow-degenerate class contains spacetimes with different redshift profiles and an explicit family of metrics within this class is presented. in the stationary, axi-symmetric case, we determine a sufficient condition for the metric to be shadow degenerate with kerr for far-away observers. again we provide two classes of examples. the first class contains metrics whose constant (boyer-lindquist-like) radius hypersurfaces are isometric to those of the kerr geometry, which is illustrated by a rotating generalization of the sv metric, obtained by a modified newman-janis algorithm. the second class of examples pertains bhs that fail to have the standard north-south z2 symmetry, but nonetheless remain shadow degenerate with kerr. the latter provides a sharp illustration that the shadow is not a probe of the horizon geometry. these examples illustrate that nonisometric bh spacetimes can cast the same shadow, albeit the lensing is generically different. | can different black holes cast the same shadow? |
we study the light rings and shadows of an uniparametric family of spherically symmetric geometries interpolating between the schwarzschild solution, a regular black hole, and a traversable wormhole, and dubbed as black bounces, all of them sharing the same critical impact parameter. we consider the ray-tracing method in order to study the impact parameter regions corresponding to the direct, lensed, and photon ring emissions, finding a broadening of all these regions for black bounce solutions as compared to the schwarzschild one. using this, we determine the optical appearance of black bounces when illuminated by three standard toy models of optically and geometrically thin accretion disks viewed in face-on orientation. | shadows and optical appearance of black bounces illuminated by a thin accretion disk |
conformal carroll symmetry generically arises on null manifolds and is important for holography of asymptotically flat spacetimes, generic black hole horizons and tensionless strings. in this paper, we focus on two dimensional (2d) null manifolds and hence on the 2d conformal carroll or equivalently the 3d bondi-metzner-sachs (bms) algebra. using carroll covariance, we write the most general free massless carroll scalar field theory and discover three inequivalent actions. of these, two viz. the time-like and space-like actions, have made their appearance in literature before. we uncover a third that we call the mixed-derivative theory. as expected, all three theories enjoy off-shell bms invariance. interestingly, we find that the on-shell symmetry of mixed derivative theory is a single virasoro algebra instead of the full bms. we discuss potential applications to tensionless strings and flat holography. | carroll covariant scalar fields in two dimensions |
black hole (bh) spectroscopy has emerged as a powerful approach to extracting spacetime information from gravitational wave (gw) observed signals. yet, quasinormal mode (qnm) spectral instability under small scale perturbations has been recently shown to be a common classical general relativistic phenomenon [j. l. jaramillo et al., phys. rev. x 11, 031003 (2021), 10.1103/physrevx.11.031003]. this requires assessing its impact on the bh qnm spectrum, in particular on bh qnm overtone frequencies. we conclude (i) perturbed bh qnm overtones are indeed potentially observable in the gw waveform, providing information on small-scale environment bh physics, and (ii) their detection poses a challenging data analysis problem of singular interest for lisa astrophysics. we adopt a twofold approach, combining theoretical results from scattering theory with a fine-tuned data analysis on a highly accurate numerical gw ringdown signal. the former introduces a set of effective parameters (partially relying on a bh weyl law) to characterize qnm instability physics. the latter provides a proof of principle demonstrating that the qnm spectral instability is indeed accessible in the time-domain gw waveform, though certainly requiring large signal-to-noise ratios. particular attention is devoted to discussing the patterns of isospectrality loss under qnm instability, since the disentanglement between axial and polar gw parities may already occur within the near-future detection range. | gravitational wave signatures of black hole quasinormal mode instability |
in this paper, we study the shadow cast by two types of charged and slowly rotating black holes in the einstein-æther theory of gravity. these two types of black holes correspond to two specific combinations of the coupling constants of the æther field, i.e., c14=0 but c123≠0 for the first type and c123=0 for the second type. for both types of black holes, in addition to the mass and charge of the black holes, we show that the presence of the æther field can also affect the size of the shadow. for the first type of black hole, it is shown that the shadow size increases with the parameter c13, while for the second type of black hole, the shadow size still increases with c13 but decreases with the parameter c14. with these properties of the æther parameters, we also discuss the observational constraints on these parameters by using the data of the first black hole image by the event horizon telescope. in addition, we also explore the effect of the æther field on the deflection angle of light and the time delay by using the gauss-bonnet theorem. it is shown that, for a specific combination c123=0 , the deflection angle/time delay is slightly affected by the æther parameter c13 at the leading order. | shadows and deflection angle of charged and slowly rotating black holes in einstein-æther theory |
superradiant instabilities of spinning black holes (bhs) can be used to impose strong constraints on ultralight bosons, thus turning bhs into effective particle detectors. however, very little is known about the development of the instability and whether its nonlinear time evolution accords to the linear intuition. for the first time, we attack this problem by studying the impact of gravitational-wave (gw) emission and gas accretion on the evolution of the instability. our quasi-adiabatic, fully-relativistic analysis shows that: (i) gw emission does not have a significant effect on the evolution of the bh, (ii) accretion plays an important role, and (iii) although the mass of the scalar cloud developed through superradiance can be a sizeable fraction of the bh mass, its energy-density is very low and backreaction is negligible. thus, massive bhs are well described by the kerr geometry even if they develop bosonic clouds through superradiance. using monte carlo methods and very conservative assumptions, we provide strong support to the validity of the linearized analysis and to the bounds of previous studies. | black holes as particle detectors: evolution of superradiant instabilities |
we show that the bekenstein-hawking entropy of a class of bps electrically charged rotating black holes in ads5 × s 5 can be obtained by a simple extremization principle. we expect that this extremization corresponds to the attractor mechanism for bps rotating black holes in five-dimensional gauged supergravity, which is still unknown. the expression to be extremized has a suggestive resemblance to anomaly polynomials and the supersymmetric casimir energy recently studied for n=4 super yang-mills. | an extremization principle for the entropy of rotating bps black holes in ads5 |
gravitational wave astronomy provides an unprecedented opportunity to test the nature of black holes and search for exotic, compact alternatives. recent studies have shown that exotic compact objects (ecos) can ring down in a manner similar to black holes, but can also produce a sequence of distinct pulses resembling the initial ringdown. these "echoes" would provide definite evidence for the existence of ecos. in this work we study the generation of these echoes in a generic, parametrized model for the eco, using green's functions. we show how to reprocess radiation in the near-horizon region of a schwarzschild black hole into the asymptotic radiation from the corresponding source in an eco spacetime. our methods allow us to understand the connection between distinct echoes and ringing at the resonant frequencies of the compact object. we find that the quasinormal mode ringing in the black hole spacetime plays a central role in determining the shape of the first few echoes. we use this observation to develop a simple template for echo waveforms. this template preforms well over a variety of eco parameters, and with improvements may prove useful in the analysis of gravitational waves. | a recipe for echoes from exotic compact objects |
we study rotating black holes in five dimensions using the nads2/ncft1 correspondence. a consistent truncation of pure einstein gravity (with a cosmological constant) in five dimensions to two dimensions gives a generalization of the jackiw-teitelboim theory that has two scalar fields: a dilaton and a squashing parameter that breaks spherical symmetry. the interplay between these two scalar fields is non trivial and leads to interesting new features. we study the holographic description of this theory and apply the results to the thermodynamics of the rotating black hole from a two dimensional point of view. this setup challenges notions of universality that have been advanced based on simpler models: we find that the mass gap of kerr-ads5 corresponds to an undetermined effective coupling in the nads2/ncft1 theory which depends on ultraviolet data. | 5d rotating black holes and the nads2/ncft1 correspondence |
we compare evolutionary predictions of double compact object merger rate densities with initial and forthcoming ligo/virgo upper limits. we find that: (i) due to the cosmological reach of advanced detectors, current conversion methods of population synthesis predictions into merger rate densities are insufficient. (ii) our optimistic models are a factor of 18 below the initial ligo/virgo upper limits for bh-bh systems, indicating that a modest increase in observational sensitivity (by a factor of ∼2.5) may bring the first detections or first gravitational wave constraints on binary evolution. (iii) stellar-origin massive bh-bh mergers should dominate event rates in advanced ligo/virgo and can be detected out to redshift z ≃ 2 with templates including inspiral, merger, and ringdown. normal stars (\lt 150 {m}⊙ ) can produce such mergers with total redshifted mass up to {m}{{tot,z}}≃ 400 {m}⊙ . (iv) high black hole (bh) natal kicks can severely limit the formation of massive bh-bh systems (both in isolated binary and in dynamical dense cluster evolution), and thus would eliminate detection of these systems even at full advanced ligo/virgo sensitivity. we find that low and high bh natal kicks are allowed by current observational electromagnetic constraints. (v) the majority of our models yield detections of all types of mergers (ns-ns, bh-ns, bh-bh) with advanced detectors. numerous massive bh-bh merger detections will indicate small (if any) natal kicks for massive bhs. | compact binary merger rates: comparison with ligo/virgo upper limits |
we study black hole linear perturbation theory in a four-dimensional schwarzschild (anti) de sitter background. when dealing with a positive cosmological constant, the corresponding spectral problem is solved systematically via the nekrasov-shatashvili functions or, equivalently, classical virasoro conformal blocks. however, this approach can be more complicated to implement for certain perturbations if the cosmological constant is negative. for these cases, we propose an alternative method to set up perturbation theory for both small and large black holes in an analytical manner. our analysis reveals a new underlying recursive structure that involves multiple polylogarithms. we focus on gravitational, electromagnetic, and conformally coupled scalar perturbations subject to dirichlet and robin boundary conditions. the low-lying modes of the scalar sector of gravitational perturbations and its hydrodynamic limit are studied in detail. | black hole perturbation theory and multiple polylogarithms |
the paper is a brief review on the existence and basic properties of static, spherically symmetric regular black hole solutions of general relativity, where the source of gravity is represented by nonlinear electromagnetic fields with the lagrangian function $l$ depending on the single invariant $f = f_{\mu\nu}f^{\mu\nu}$ or on two variables: either $l(f, h)$, where $h = {^*}f_{\mu\nu} f^{\mu\nu}$, where ${^*}f_{\mu\nu}$ is the hodge dual of $f_{\mu\nu}$, or $l(f, j)$, where $j = f_{\mu\nu}f^{\nu\rho} f_{\rho\sigma} f^{\sigma\mu}$. a number of no-go theorems are discussed, revealing the conditions under which the space-time cannot have a regular center, among which the theorems concerning $l(f,j)$ theories are probably new. these results concern both regular black holes and regular particlelike or starlike objects (solitons) without horizons. thus, a regular center in solutions with an electric charge $q_e\ne 0$ is only possible with nonlinear electrodynamics (ned) having no maxwell weak field limit. regular solutions with $l(f)$ and $l(f, j)$ ned, possessing a correct (maxwell) weak-field limit, are possible if the system contains only a magnetic charge $q_m \ne 0$. it is shown, however, that in such solutions the causality and unitarity as well as dynamic stability conditions are inevitably violated in a neighborhood of the center. some particular examples are discussed. | regular black holes sourced by nonlinear electrodynamics |
we study the charges and first law of thermodynamics for accelerating, non-rotating black holes with dyonic charges in ads4 using the covariant phase space formalism. in order to apply the formalism to these solutions (which are asymptotically locally ads and admit a non-smooth conformal boundary i ) we make two key improvements: (1) we relax the requirement to impose dirichlet boundary conditions and demand merely a well-posed variational problem. (2) we keep careful track of the codimension-2 corner term induced by the holographic counterterms, a necessary requirement due to the presence of "cosmic strings" piercing i . using these improvements we are able to match the holographic noether charges to the wald hamiltonians of the covariant phase space and derive the first law of black hole thermodynamics with the correct "thermodynamic length" terms arising from the strings. we investigate the relationship between the charges imposed by supersymmetry and show that our first law can be consistently applied to various classes of non-supersymmetric solutions for which the cross-sections of the horizon are spindles. | thermodynamics of accelerating ads4 black holes from the covariant phase space |
in this paper, we investigate gluing together two anti-de sitter (ads) geometries along a timelike brane, which corresponds to coupling two brane field theories (bfts) through gravitational interactions in the dual holographic perspective. by exploring the general conditions for this gluing process, we show that the energy stress tensors of the bfts backreact on the dynamical metric in a manner reminiscent of the ttbar deformation. in particular, we present explicit solutions for the three-dimensional case with chiral excitations and further construct perturbative solutions with non-chiral excitations. | gluing ads/cft |
we derive several new reformulations of the hubeny-rangamani-takayanagi covariant holographic entanglement entropy formula. these include: (1) a minimax formula, which involves finding a maximal-area achronal surface on a timelike hypersurface homologous to d(a) (the boundary causal domain of the region a whose entropy we are calculating) and minimizing over the hypersurface; (2) a max v-flow formula, in which we maximize the flux through d(a) of a divergenceless bulk 1-form v subject to an upper bound on its norm that is non-local in time; and (3) a min u-flow formula, in which we minimize the flux over a bulk cauchy slice of a divergenceless timelike 1-form u subject to a lower bound on its norm that is non-local in space. the two flow formulas define convex programs and are related to each other by lagrange duality. for each program, the optimal configurations dynamically find the hrt surface and the entanglement wedges of a and its complement. the v-flow formula is the covariant version of the freedman-headrick bit thread reformulation of the ryu-takayanagi formula. we also introduce a measure-theoretic concept of a "thread distribution", and explain how riemannian flows, v-flows, and u-flows can be expressed in terms of thread distributions. | covariant bit threads |
understanding how to prepare and count black hole micro-states by using the gravitational path integral is one of the most important problems in quantum gravity. nevertheless, a state-by-state count of black hole microstates is difficult because the apparent number of degrees of freedom available in the gravitational effective theory can vastly exceed the entropy of the black hole, even in the special case of bps black holes. in this paper, we show that we can use the gravitational path integral to prepare a basis for the hilbert space of all bps black hole microstates. we find that the dimension of this hilbert space computed by an explicit state count is in complete agreement with the degeneracy obtained from the gibbons-hawking prescription. specifically, this match includes all non-perturbative corrections in $1/g_n$. such corrections are, in turn, necessary in order for this degeneracy of bps states to match the non-perturbative terms in the $1/g_n$ expansion in the string theory count of such microstates. | constructing all bps black hole microstates from the gravitational path integral |
the near-zone "love" symmetry resolves the naturalness issue of black hole love number vanishing with sl (2, &r;) representation theory. here, we generalize this proposal to 5-dimensional asymptotically flat and doubly spinning (myers-perry) black holes. we consider the scalar response of myers-perry black holes and extract its static scalar love numbers. in agreement with the naturalness arguments, these love numbers are, in general, non-zero and exhibit logarithmic running unless certain resonant conditions are met; these conditions include new cases with no previously known analogs. we show that there exist two near-zone truncations of the equations of motion that exhibit enhanced sl (2, &r;) love symmetries that explain the vanishing of the static scalar love numbers in the resonant cases. these love symmetries can be interpreted as local sl (2, &r;) sl (2, &r;) near-zone symmetries spontaneously broken down to global sl (2, &r;) × u (1) symmetries by the periodic identification of the azimuthal angles. we also discover an infinite-dimensional extension of the love symmetry into sl (2, &r;) ⋉u ̂(1)v2 that contains both love symmetries as particular subalgebras, along with a family of sl (2, &r;) subalgebras that reduce to the exact near-horizon myers-perry black hole isometries in the extremal limit. finally, we show that the love symmetries acquire a geometric interpretation as isometries of subtracted (effective) black hole geometries that preserve the internal structure of the black hole and interpret these non-extremal sl (2, &r;) structures as remnants of the enhanced isometry of the near-horizon extremal geometries. | scalar love numbers and love symmetries of 5-dimensional myers-perry black holes |
we study the shadow cast by the higher-dimensional schwarzschild-tangherlini black hole, and analytically calculate the influence of extra dimensions on the shadow of a black hole. a black hole casts a shadow as an optical appearance because of its strong gravitational field which is known to be a dark zone covered by a circle for a schwarzschild black hole. we demonstrate that the null geodesic equation can be integrated by hamilton-jacobi approach, which enable us to investigate the shadow cast by the higher-dimensional schwarzschild-tangherlini black holes. interestingly, it turns out that, for fixed values of the mass parameter, the shadow in higher-dimensional spacetimes are smaller when compared with four-dimensional schwarzschild black hole. further, the shadows of higher-dimensional schwarzschild-tangherlini black holes are concentric circles with radius of the circle decreases with increase in d. we visualize the photon regions and the shadows in various dimensions for different values of the parameters, and the energy emission rates are is also investigated. our results, in the limit d = 4, reduced exactly to vis-à-vis schwarzschild black hole case. | shadow of schwarzschild-tangherlini black holes |
motivated by high interest in the close relation between string theory and black hole solutions, in this paper, we take into account the einstein-gauss-bonnet lagrangian in the context of massive gravity. we examine the possibility of black hole in this regard, and discuss the types of horizons. next, we calculate conserved and thermodynamic quantities and check the validity of the first law of thermodynamics. in addition, we investigate the stability of these black holes in context of canonical ensemble. we show that number, type and place of phase transition points may be significantly affected by different parameters. next, by considering cosmological constant as thermodynamical pressure, we will extend phase space and calculate critical values. then, we construct thermodynamical spacetime by considering mass as thermodynamical potential. we study geometrical thermodynamics of these black holes in context of heat capacity and extended phase space. we show that studying heat capacity, geometrical thermodynamics and critical behavior in extended phase space lead to consistent results. finally, we will employ a new method for obtaining critical values and show that the results of this method are consistent with those of other methods. | charged black hole solutions in gauss-bonnet-massive gravity |
ligo and virgo have reported the detection of gw190521, from the merger of a binary black hole (bbh) with a total mass around 150 m⊙. while current stellar models limit the mass of any black hole (bh) remnant to about 40-50 m⊙, more massive bhs can be produced dynamically through repeated mergers in the core of a dense star cluster. the process is limited by the recoil kick (due to anisotropic emission of gravitational radiation) imparted to merger remnants, which can escape the parent cluster, thereby terminating growth. we study the role of the host cluster metallicity and escape speed in the buildup of massive bhs through repeated mergers. almost independent of host metallicity, we find that a bbh of about 150 m⊙ could be formed dynamically in any star cluster with escape speed ≳200 km s-1, as found in galactic nuclear star clusters as well as the most massive globular clusters and super star clusters. using an inspiral-only waveform, we compute the detection probability for different primary masses (≥60 m⊙) as a function of secondary mass and find that the detection probability increases with secondary mass and decreases for larger primary mass and redshift. future additional detections of massive bbh mergers will be of fundamental importance for understanding the growth of massive bhs through dynamics and the formation of intermediate-mass bhs. | on the origin of gw190521-like events from repeated black hole mergers in star clusters |
short gamma-ray bursts are believed to arise from compact binary mergers (either neutron star-neutron star or black hole-neutron star). if so, their jets must penetrate outflows that are ejected during the merger. as a jet crosses the ejecta, it dissipates its energy, producing a hot cocoon that surrounds it. we present here 3d numerical simulations of jet propagation in mergers' outflows, and we calculate the resulting emission. this emission consists of two components: the cooling emission, the leakage of the thermal energy of the hot cocoon, and the cocoon macronova that arises from the radioactive decay of the cocoon's material. this emission gives a brief (∼1 h) blue, wide angle signal. while the parameters of the outflow and jet are uncertain, for the configurations we have considered, the signal is bright (∼-14 to -15 absolute magnitude) and outshines all other predicted ultraviolet-optical signals. the signal is brighter when the jet breakout time is longer, and its peak brightness does not depend strongly on the highly uncertain opacity. a rapid search for such a signal is a promising strategy to detect an electromagnetic merger counterpart. a detected candidate could be then followed by deep infrared searches for the longer but weaker macronova arising from the rest of the ejecta. | the cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers |
we evaluate finite part of the on-shell action for black brane solutions of einstein gravity on different subregions of spacetime enclosed by null boundaries. these subregions include the intersection of the wheeler-dewitt patch with past/future interior and left/right exterior for a two-sided black brane. identifying the on-shell action on the exterior regions with subregion complexity, one finds that it obeys the subadditivity condition. this gives an insight to define a new quantity named mutual complexity. we will also consider a certain subregion that is a part of spacetime, which could be causally connected to an operator localized behind/outside the horizon. taking into account all terms needed to have a diffeomorphism-invariant action with a well-defined variational principle, one observes that the main contribution that results in a nontrivial behavior of the on-shell action comes from joint points where two lightlike boundaries (including the horizon) intersect. a spacelike boundary gives rise to a linear time growth, while we have a classical contribution due to a timelike boundary that is given by the free energy. | black hole subregion action and complexity |
in the ads /cft correspondence, states obtained by hamiltonian evolution of the thermofield doubled state are also dual to an eternal black-hole geometry, which is glued to the boundary with a time shift generated by a large diffeomorphism. we describe gauge-invariant relational observables that probe the black hole interior in these states and constrain their properties using effective field theory. by adapting recent versions of the information paradox we show that these observables are necessarily described by state-dependent bulk-boundary maps, which we construct explicitly. | local operators in the eternal black hole |
the analytic continuation of the general signature (1, 3) lorentzian kerr-taub-nut black holes to signature (2, 2) kleinian black holes is studied. their global structure is characterized by a toric penrose diagram resembling their lorentzian counterparts. kleinian black holes are found to be self-dual when their mass and nut charge are equal for any value of the kerr rotation parameter a. remarkably, it is shown that the rotation a can be eliminated by a large diffeomorphism; this result also holds in euclidean signature. the continuation from lorentzian to kleinian signature is naturally induced by the analytic continuation of the s-matrix. indeed, we show that the geometry of linearized black holes, including kerr-taub-nut, is captured by (2, 2) three-point scattering amplitudes of a graviton and a massive spinning particle. this stands in sharp contrast to their lorentzian counterparts for which the latter vanishes kinematically and enables a direct link to the s-matrix. | black holes in klein space |
the gravitational dual to the grand canonical ensemble of a large n holographic theory is a charged black hole. these spacetimes — for example reissner- nordström-ads — can have cauchy horizons that render the classical gravitational dynamics of the black hole interior incomplete. we show that a (spatially uniform) deformation of the cft by a neutral scalar operator generically leads to a black hole with no inner horizon. there is instead a spacelike kasner singularity in the interior. for relevant deformations, cauchy horizons never form. for certain irrelevant deformations, cauchy horizons can exist at one specific temperature. we show that the scalar field triggers a rapid collapse of the einstein-rosen bridge at the would-be cauchy horizon. finally, we make some observations on the interior of charged dilatonic black holes where the kasner exponent at the singularity exhibits an attractor mechanism in the low temperature limit. | gravitational duals to the grand canonical ensemble abhor cauchy horizons |
black hole (bh) triples represent one of the astrophysical pathways for bh mergers in the universe detectable by ligo and virgo. we study the formation of bh triples via binary-binary encounters in dense clusters, showing that up to two-thirds of the triples formed through this channel are hierarchical, whereas the remaining one-third are in a non-hierarchical, unstable configuration. we built a database of 32 000 n-body simulations to investigate the evolution of bh triples focusing on mildly hierarchical and non-hierarchical unstable configurations. varying the mutual orbital inclination, the three bh masses and the inner and outer eccentricities, we show that retrograde, nearly planar configurations lead to a significant shrinkage of the inner binary. we find a universal trend of triple systems, namely that they tend to evolve toward prograde configurations and that the orbital flip, driven by the torque exerted on the inner bh binary (bhb) by the outer bh, leads in general to tighter inner orbits. in some cases, the resulting bhb undergoes coalescence within a hubble time, releasing gravitational waves. a large fraction of merging bhbs with an initial separation of 1 au enter the 10−3 − 10−1 hz frequency band with large eccentricities, thus representing potential eccentric lisa sources. mergers originating from an initially tighter bhb (a ∼ 0.01 au), instead often have eccentricities above 0.7 in the 1 hz band. we find that the mass distribution of the mergers in this astrophysical channel maps the original bh binary spectrum. this might have interesting consequences in light of the growing population of bh mergers detected by ligo and virgo, namely that eccentric sources detected in high-frequency detectors are most likely connected with a high-velocity dispersion stellar environment, whereas eccentric sources detected in low-frequency detectors are likely to develop in low-density clusters. | order in the chaos. eccentric black hole binary mergers in triples formed via strong binary-binary scatterings |
a star that approaches a supermassive black hole (smbh) on a circular extreme mass ratio inspiral (emri) can undergo roche lobe overflow (rlof), resulting in a phase of long-lived mass transfer onto the smbh. if the interval separating consecutive emris is less than the mass-transfer timescale driven by gravitational wave emission (typically ~1-10 myr), the semimajor axes of the two stars will approach each another on scales of ≲ hundreds to thousands of gravitational radii. close flybys tidally strip gas from one or both rlofing stars, briefly enhancing the mass-transfer rate onto the smbh and giving rise to a flare of transient x-ray emission. if both stars reside in a common orbital plane, these close interactions will repeat on a timescale as short as hours, generating a periodic series of flares with properties (amplitudes, timescales, sources lifetimes) remarkably similar to the "quasi-periodic eruptions" (qpes) recently observed from galactic nuclei hosting low-mass smbhs. a cessation of qpe activity is predicted on a timescale of months to years, due to nodal precession of the emri orbits out of alignment by the smbh spin. channels for generating the requisite coplanar emris include the tidal separation of binaries (hills mechanism) or type i inward migration through a gaseous agn disk. alternative stellar dynamical scenarios for qpes, that invoke single stellar emris on an eccentric orbit undergoing a runaway sequence of rlof events, are strongly disfavored by formation rate constraints. | interacting stellar emris as sources of quasi-periodic eruptions in galactic nuclei |
the thermodynamics for kerr-ads black hole in four dimensions is revisited using the recently proposed restricted phase space formalism, which includes the central charge c of the dual cft and the chemical potential μ , but excludes the pressure and the conjugate volume, as thermodynamic variables. the euler relation holds automatically, and the first order homogeneity of the mass and the zeroth order homogeneity of the intensive variables are made explicit. thermodynamic processes involving each pair of conjugate variables are studied in some detail, with emphasis on the scaling properties of the equations of states. it turns out that the thermodynamic behavior of the kerr-ads black hole is very similar to that of the rn-ads black hole studied earlier. in particular, it is found that, there is a first order supercritical phase equilibrium in the t -s processes at fixed nonvanishing angular momentum, while at vanishing angular momentum or at fixed angular velocities, there is always a non-equilibrium transition from a small unstable black hole state to a large stable black hole state. moreover, there is a hawking-page phase transition in the μ -c processes. due to the complicatedness of the kerr metric, the exact critical point and the hawking-page temperature are worked out explicitly only in the slow rotating limit, however the characteristic thermodynamic properties do not rely on the slow rotating approximation. | thermodynamics of kerr-ads black holes in the restricted phase space |
the formation of merging binary black holes can occur through multiple astrophysical channels such as, e.g., isolated binary evolution and dynamical formation or, alternatively, have a primordial origin. increasingly large gravitational-wave catalogs of binary black-hole mergers have allowed for the first model selection studies between different theoretical predictions to constrain some of their model uncertainties and branching ratios. in this work, we show how one could add an additional and independent constraint to model selection by using the stochastic gravitational-wave background. in contrast to model selection analyses that have discriminating power only up to the gravitational-wave detector horizons (currently at redshifts z ≲ 1 for ligo-virgo), the stochastic gravitational-wave background accounts for the redshift integration of all gravitational-wave signals in the universe. as a working example, we consider the branching ratio results from a model selection study that includes potential contribution from astrophysical and primordial channels. we renormalize the relative contribution of each channel to the detected event rate to compute the total stochastic gravitational-wave background energy density. the predicted amplitude lies below the current observational upper limits of gwtc-3 by ligo-virgo, indicating that the results of the model selection analysis are not ruled out by current background limits. furthermore, given the set of population models and inferred branching ratios, we find that, even though the predicted background will not be detectable by current generation gravitational-wave detectors, it will be accessible by third-generation detectors such as the einstein telescope and space-based detectors such as lisa. | stochastic gravitational-wave background as a tool for investigating multi-channel astrophysical and primordial black-hole mergers |
in the present paper, we show the existence of a fully nonlinear mechanism for the formation of scalarized black holes, which is different from the spontaneous scalarization, and demonstrate its dynamical development. we consider a class of scalar-gauss-bonnet gravity theories within which no tachyonic instability can occur. although the schwarzschild black holes are linearly stable against scalar perturbations, we show dynamically that for certain choices of the coupling function, they are unstable against nonlinear scalar perturbations. this nonlinear instability leads to the formation of new black holes with scalar hair. the fully nonlinear and self-consistent study of the equilibrium black holes reveals that the spectrum of solutions is more complicated and more than one scalarized branch can exist. we have also considered classes of scalar-gauss-bonnet theories where both the standard and the nonlinear scalarization can be present, and they are smoothly connected that completes in an interesting way the picture of black hole scalarization. the fully nonlinear (de)scalarization of a schwarzschild black hole will always happen with a jump because the stable "scalarized branch" is not continuously connected to the schwarzschild one that can leave clear observational signatures. | beyond the spontaneous scalarization: new fully nonlinear mechanism for the formation of scalarized black holes and its dynamical development |
the ringdown and shadow of the astrophysically significant kerr black hole (bh) are both intimately connected to a special set of bound null orbits known as light rings (lrs). does it hold that a generic equilibrium bh must possess such orbits? in this letter we prove the following theorem. a stationary, axisymmetric, asymptotically flat black hole spacetime in 1 +3 dimensions, with a nonextremal, topologically spherical, killing horizon admits, at least, one standard lr outside the horizon for each rotation sense. the proof relies on a topological argument and assumes c2 smoothness and circularity, but makes no use of the field equations. the argument is also adapted to recover a previous theorem establishing that a horizonless ultracompact object must admit an even number of nondegenerate lrs, one of which is stable. | stationary black holes and light rings |
future third-generation (3g) ground-based gravitational wave (gw) detectors, such as the einstein telescope and cosmic explorer, will have unprecedented sensitivities enabling studies of the entire population of stellar mass binary black hole coalescences in the universe, while the a + and voyager upgrades to current detectors will significantly improve over advanced ligo and virgo design sensitivities. to infer binary parameters from a gw signal we require accurate models of the gravitational waveform as a function of black hole masses, spins, etc. such waveform models are built from numerical relativity (nr) simulations and/or semianalytical expressions in the inspiral. we investigate the limits of the current waveform models and study at what detector sensitivity these models will yield unbiased parameter inference for loud "golden" binary black hole systems, what biases we can expect beyond these limits, and what implications such biases will have for gw astrophysics. for 3g detectors we find that the mismatch error for semianalytical models needs to be reduced by at least three orders of magnitude and for nr waveforms by one order of magnitude. we show that typical biases in units of standard deviations for the mass-ratio and effective aligned-spin will be of order unity for 2g design sensitivity and will reach several tens for 3g networks. in addition, we show that for a population of one hundred high mass precessing binary black holes, measurement errors sum up to a sizable population bias, about 10-30 times larger than the sum of 90% credible intervals for chirp mass, mass-ratio, effective aligned, and precessing spin parameters. furthermore, we demonstrate that the residual signal between the gw data recorded by a detector and the best fit template waveform obtained by parameter inference analyses can have significant signal-to-noise ratio and can lead to bayes factors as high as 1011 between a coherent and an incoherent wavelet model for the population events. this coherent power left in the residual could lead to the observation of erroneous deviations from general relativity. to address these issues and be ready to reap the scientific benefits of 3g gw detectors in the 2030s, waveform models that are significantly more physically complete and accurate need to be developed in the next decade along with major advances in efficiency and accuracy of nr codes. | gravitational waveform accuracy requirements for future ground-based detectors |
we derive the hyperbolic orbit of binary black holes with electric and magnetic charges. in the low-velocity and weak-field regime, by using the newtonian method, we calculate the total emission rate of energy due to gravitational and electromagnetic radiation from binary black holes with electric and magnetic charges in hyperbolic orbits. moreover, we develop a formalism to derive the merger rate of binary black holes with electric and magnetic charges from the two-body dynamical capture. we apply the formalism to investigate the effects of the charges on the merger rate for the near-extremal case and find that the effects cannot be ignored. | gravitational and electromagnetic radiation from binary black holes with electric and magnetic charges: hyperbolic orbits on a cone |
: it was recently shown that strong cosmic censorship might be violated for near-extremally-charged black holes in 4-dimensional de sitter space under scalar perturbations. here, we extend the study of neutral massless scalar perturbations in higher dimensions and discuss the dimensional influence on the validity of strong cosmic censorship hypothesis. by giving an elaborate description of neutral massless scalar perturbations of reissner-nordström-de sitter black holes in d = 4 , 5 and 6 dimensions we conclude that strong cosmic censorship is violated near extremality. | strong cosmic censorship in higher-dimensional reissner-nordström-de sitter spacetime |
recently, a novel four-dimensional einstein-gauss-bonnet (4egb) theory of gravity was proposed by glavan and lin [d. glavan and c. lin, phys. rev. lett. 124, 081301 (2020)], which includes a regularized gauss-bonnet term using the re-scalaring of the gauss-bonnet coupling constant $\alpha \to \alpha/(d-4)$ in the limit $d\to 4$ . this theory has also been reformulated to a specific class of the horndeski theory with an additional scalar degree of freedom and to a spatial covariant version with a lagrangian multiplier, which can eliminate the scalar mode. here, we study the physical properties of the electromagnetic radiation emitted from a thin accretion disk around a static spherically symmetric black hole in 4egb gravity. for this purpose, we assume the disk is in a steady-state and in hydrodynamic and thermodynamic equilibrium, so that the emitted electromagnetic radiation is a black body spectrum. we study in detail the effects of the gauss-bonnet coupling constant $\alpha$ in 4egb gravity on the energy flux, temperature distribution, and electromagnetic spectrum of the disk. with an increase in the parameter $\alpha$ , the energy flux, temperature distribution, and electromagnetic spectrum of the accretion disk all increase. we also show that the accretion efficiency increases with the growth of the parameter $\alpha$ . our results indicate that the thin accretion disk around a static spherically symmetric black hole in 4egb gravity is hotter, more luminous, and more efficient than that around a schwarzschild black hole with the same mass for positive $\alpha$ , while it is cooler, less luminous, and less efficient for negative $\alpha$ . * supported by national natural science foundation of china (11675143), the zhejiang provincial natural science foundation of china (ly20a050002) and the fundamental research funds for the provincial universities of zhejiang in china (rf-a2019015) | thin accretion disk around a four-dimensional einstein-gauss-bonnet black hole |
thanks to the release of the extraordinary eht image of shadow attributed to the m87* supermassive black hole (smbh), we have a novel window to assess the validity of fundamental physics in the strong-field regime. motivated by this, we consider johannsen & psaltis metric parameterized by mass, spin, and an additional dimensionless hair parameter ϵ. this parametric framework in the high rotation regimes provides a well-behaved bed to the strong-gravity test of the no-hair theorem (nht) using the eht data. incorporating the ϵ into the standard kerr spacetime enrich it in the sense that, depending on setting the positive and negative values for that, we deal with alternative compact objects: deformed kerr naked singularity and kerr bh solutions, respectively. shadows associated with these two possible solutions indicate that the deformation parameter ϵ affects the geometry shape of standard shadow such that it becomes more oblate and prolate with ϵ<0 and ϵ>0, respectively. by scanning the window associated with three shadow observables oblateness, deviation from circularity, and shadow diameter, we perform a numerical analysis within the range a*=0.9∓0.1 of the dimensionless rotation parameter, to find the constraints on the hair parameter ϵ in both possible solutions. for both possible signs of ϵ, we extract a variety of upper bounds that are in interplay with a*. although by approaching the rotation parameters to the extreme limit, the allowable range of both hair parameters becomes narrower, the hairy kerr bh solution is a more promising candidate to play the role of the alternative compact object instead of the standard kerr bh. the lack of tension between hairy kerr bh with the current observation of the eht shadow of the m87* smbh carries this message that there is the possibility of nht violation. | no-hair theorem in the wake of event horizon telescope |
the study of higher-dimensional black holes is a subject which has recently attracted vast interest. perhaps one of the most surprising discoveries is a realization that the properties of higher-dimensional black holes with the spherical horizon topology and described by the kerr-nut-(a)ds metrics are very similar to the properties of the well known four-dimensional kerr metric. this remarkable result stems from the existence of a single object called the principal tensor. in our review we discuss explicit and hidden symmetries of higher-dimensional kerr-nut-(a)ds black hole spacetimes. we start with discussion of the killing and killing-yano objects representing explicit and hidden symmetries. we demonstrate that the principal tensor can be used as a "seed object" which generates all these symmetries. it determines the form of the geometry, as well as guarantees its remarkable properties, such as special algebraic type of the spacetime, complete integrability of geodesic motion, and separability of the hamilton-jacobi, klein-gordon, and dirac equations. the review also contains a discussion of different applications of the developed formalism and its possible generalizations. | black holes, hidden symmetries, and complete integrability |
we compute the quasi-bound state spectra of ultralight scalar and vector fields around rotating black holes. these spectra are determined by the gravitational fine structure constant α, which is the ratio of the size of the black hole to the compton wavelength of the field. when α is small, the energy eigenvalues and instability rates can be computed analytically. since the solutions vary rapidly near the black hole horizon, ordinary perturbative approximations fail and we must use matched asymptotic expansions to determine the spectra. our analytical treatment relies on the separability of the equations of motion, and is therefore only applicable to the scalar field and the electric modes of the vector field. however, for slowly-rotating black holes, the equations for the magnetic modes can be written in a separable form, which we exploit to derive their energy eigenvalues and conjecture an analytic form for their instability rates. to check our conjecture, and to extend all results to large values of α, we solve for the spectra numerically. we explain how to accurately and efficiently compute these spectra, without relying on separability. this allows us to obtain reliable results for any α gtrsim 0.001 and black holes of arbitrary spin. our results provide an essential input to the phenomenology of boson clouds around black holes, especially when these are part of binary systems. | the spectra of gravitational atoms |
motivated by the desire to understand chaos in the s-matrix of string theory, we study tree level scattering amplitudes involving highly excited strings. while the amplitudes for scattering of light strings have been a hallmark of string theory since its early days, scattering of excited strings has been far less studied. recent results on black hole chaos, combined with the correspondence principle between black holes and strings, suggest that the amplitudes have a rich structure. we review the procedure by which an excited string is formed by repeatedly scattering photons off of an initial tachyon (the ddf formalism). we compute the scattering amplitude of one arbitrary excited string and any number of tachyons in bosonic string theory. at high energies and high mass excited state these amplitudes are determined by a saddle-point in the integration over the positions of the string vertex operators on the sphere (or the upper half plane), thus yielding a generalization of the "scattering equations". we find a compact expression for the amplitude of an excited string decaying into two tachyons, and study its properties for a generic excited string. we find the amplitude is highly erratic as a function of both the precise excited string state and of the tachyon scattering angle relative to its polarization, a sign of chaos. | chaotic scattering of highly excited strings |
the dynamics of precessing binary black holes (bbhs) in the post-newtonian regime has a strong timescale hierarchy: the orbital timescale is very short compared to the spin-precession timescale which, in turn, is much shorter than the radiation-reaction timescale on which the orbit is shrinking due to gravitational-wave emission. we exploit this timescale hierarchy to develop a multiscale analysis of bbh dynamics elaborating on the analysis of kesden et al. [phys. rev. lett. 114, 081103 (2015)]. we solve the spin-precession equations analytically on the precession time and then implement a quasiadiabatic approach to evolve these solutions on the longer radiation-reaction time. this procedure leads to an innovative "precession-averaged" post-newtonian approach to studying precessing bbhs. we use our new solutions to classify bbh spin precession into three distinct morphologies, then investigate phase transitions between these morphologies as bbhs inspiral. these precession-averaged post-newtonian inspirals can be efficiently calculated from arbitrarily large separations, thus making progress towards bridging the gap between astrophysics and numerical relativity. | multi-timescale analysis of phase transitions in precessing black-hole binaries |
we study the large n limit of some supersymmetric partition functions of the u(n)k × u(n)−k abjm theory computed by supersymmetric localization. we conjecture an explicit expression, valid to all orders in the large n limit, for the partition function on the u(1) × u(1) invariant squashed sphere in the presence of real masses in terms of an airy function. several non-trivial tests of this conjecture are presented. in addition, we derive an explicit compact expression for the topologically twisted index of the abjm theory valid at fixed k to all orders in the 1/n expansion. we use these results to derive the topologically twisted index and the sphere partition function in the 't hooft limit which correspond to genus g type iia string theory free energies to all orders in the α' expansion. we discuss the implications of our results for holography and the physics of ads4 black holes. | large n partition functions of the abjm theory |
while singularities are inevitable in the classical theory of general relativity, it is commonly believed that they will not be present when quantum gravity effects are taken into account in a consistent framework. in particular, the structure of black holes should be modified in frameworks beyond general relativity that aim at regularizing singularities. being agnostic on the nature of such theory, in this paper we classify the possible alternatives to classical black holes and provide a minimal set of phenomenological parameters that describe their characteristic features. the introduction of these parameters allows us to study, in a largely model-independent manner and taking into account all the relevant physics, the phenomenology associated with these quantum-modified black holes. we perform an extensive analysis of different observational channels and obtain the most accurate characterization of the viable constraints that can be placed using current data. aside from facilitating a critical revision of previous work, this analysis also allows us to highlight how different channels are capable of probing certain features but are oblivious to others, and pinpoint the theoretical aspects that should be addressed in order to strengthen these tests. | phenomenological aspects of black holes beyond general relativity |
as part of our massive spectroscopic survey of 25 galactic globular clusters with muse, we performed multiple epoch observations of ngc 3201 with the aim of constraining the binary fraction. in this cluster, we found one curious star at the main-sequence turn-off with radial velocity variations of the order of 100 km s- 1, indicating the membership to a binary system with an unseen component since no other variations appear in the spectra. using an adapted variant of the generalized lomb-scargle periodogram, we could calculate the orbital parameters and found the companion to be a detached stellar-mass black hole with a minimum mass of 4.36 ± 0.41 m⊙. the result is an important constraint for binary and black hole evolution models in globular clusters as well as in the context of gravitational wave sources. | a detached stellar-mass black hole candidate in the globular cluster ngc 3201 |
we argue that in theories of quantum gravity with discrete gauge symmetries, e.g. zk , the gauge couplings of u(1) gauge symmetries become weak in the limit of large k, as g → k-α with α a positive order 1 coefficient. the conjecture is based on black hole arguments combined with the weak gravity conjecture (or the bps bound in the supersymmetric setup), and the species bound. we provide explicit examples based on type iib on ads5×s5/zk orbifolds, and m-theory on ads4×s7/zk abjm orbifolds (and their type iia reductions). we study ads4 vacua of type iia on cy orientifold compactifications, and show that the parametric scale separation in certain infinite families is controlled by a discrete zk symmetry for domain walls. we accordingly propose a refined version of the strong ads distance conjecture, including a parametric dependence on the order of the discrete symmetry for 3-forms. | discrete symmetries, weak coupling conjecture and scale separation in ads vacua |
the origin of the supermassive black holes that inhabit the centres of massive galaxies remains unclear1,2. direct-collapse black holes—remnants of supermassive stars, with masses around 10,000 times that of the sun—are ideal seed candidates3-6. however, their very existence and their formation environment in the early universe are still under debate, and their supposed rarity makes modelling their formation difficult7,8. models have shown that rapid collapse of pre-galactic gas (with a mass infall rate above some critical value) in metal-free haloes is a requirement for the formation of a protostellar core that will then form a supermassive star9,10. here we report a radiation hydrodynamics simulation of early galaxy formation11,12 that produces metal-free haloes massive enough and with sufficiently high mass infall rates to form supermassive stars. we find that pre-galactic haloes and their associated gas clouds that are exposed to a lyman-werner intensity roughly three times the intensity of the background radiation and that undergo at least one period of rapid mass growth early in their evolution are ideal environments for the formation of supermassive stars. the rapid growth induces substantial dynamical heating13,14, amplifying the lyman-werner suppression that originates from a group of young galaxies 20 kiloparsecs away. our results strongly indicate that the dynamics of structure formation, rather than a critical lyman-werner flux, is the main driver of the formation of massive black holes in the early universe. we find that the seeds of massive black holes may be much more common than previously considered in overdense regions of the early universe, with a co-moving number density up to 10-3 per cubic megaparsec. | formation of massive black holes in rapidly growing pre-galactic gas clouds |
we address some issues in higher-derivative gauged supergravity with chern-simons terms, focusing on the five-dimensional case. we discuss the variational problem with dirichlet boundary conditions as well as holographic renormalization in asymptotically locally ads spacetimes, and derive the corresponding boundary terms. we then employ wald's formalism in order to define conserved charges associated to local symmetries (diffeomorphisms and u(1) gauge transformations), taking into account the effect of generic gauge chern-simons terms. we prove that the first law of black hole mechanics and the quantum statistical relation hold in this setup. chern-simons terms also lead us to distinguish between noether charges and page (or komar) charges which satisfy the gauss law. we make use of the latter to compute corrections to the angular momentum and electric charge of the supersymmetric black hole in ads5 from its corrected near-horizon geometry. this also allows us to derive the microcanonical form of the entropy as a function of the conserved charges relying entirely on the near-horizon geometry. finally, we comment on four-derivative gauged supergravity in four dimensions, showing that field redefinitions permit to simplify the action at linear order in the corrections, so that the equations of motion are those of the two-derivative theory. | boundary terms and conserved charges in higher-derivative gauged supergravity |
kerr-adsd+1 black holes for d ≥ 3 suffer from classical superradiant instabilities over a range of masses above extremality. we conjecture that these instabilities settle down into grey galaxies (ggs) — a new class of coarse-grained solutions to einstein's equations which we construct in d = 3. grey galaxies are made up of a black hole with critical angular velocity ω = 1 in the `centre' of ads, surrounded by a large flat disk of thermal bulk gas that revolves around the centre of ads at the speed of light. the gas carries a finite fraction of the total energy, as its parametrically low energy density and large radius are inversely related. ggs exist at masses that extend all the way down to the unitarity bound. their thermodynamics is that of a weakly interacting mix of kerr-ads black holes and the bulk gas. their boundary stress tensor is the sum of a smooth `black hole' contribution and a peaked gas contribution that is delta function localized around the equator of the boundary sphere in the large n limit. we also construct another class of solutions with the same charges; `revolving black holes (rbhs)'. rbhs are macroscopically charged so(d, 2) descendants of ads-kerr solutions, and consist of ω = 1 black holes revolving around the centre of ads at a fixed radial location but in a quantum wave function in the angular directions. rbh solutions are marginally entropically subdominant to gg solutions and do not constitute the endpoint of the superradiant instability. nonetheless, we argue that supersymmetric versions of these solutions have interesting implications for the spectrum of supersymmetric states in, e.g. n = 4 yang-mills theory. | grey galaxies' as an endpoint of the kerr-ads superradiant instability |
we present a detailed study of the methodology for correlating `dark sirens' (compact binaries coalescences without electromagnetic counterpart) with galaxy catalogs. we propose several improvements on the current state of the art, and we apply them to the gwtc-2 catalog of ligo/virgo gravitational wave (gw) detections, and the glade galaxy catalog, performing a detailed study of several sources of systematic errors that, with the expected increase in statistics, will eventually become the dominant limitation. we provide a measurement of h0 from dark sirens alone, finding as the best result h0 = 67.3+27.6-17.9 km s-1 mpc-1 (68% c.l.) which is, currently, the most stringent constraint obtained using only dark sirens. combining dark sirens with the counterpart for gw170817 we find h0 = 72.2+13.9-7.5 km s-1 mpc-1. we also study modified gw propagation, which is a smoking gun of dark energy and modifications of gravity at cosmological scales, and we show that current observations of dark sirens already start to provide interesting limits. from dark sirens alone, our best result for the parameter ξ0 that measures deviations from gr (with ξ0 = 1 in gr) is ξ0 = 2.1+3.2-1.2. we finally discuss limits on modified gw propagation under the tentative identification of the flare ztf19abanrhr as the electromagnetic counterpart of the binary black hole coalescence gw190521, in which case our most stringent result is ξ0 = 1.8+0.9-0.6. we release the publicly available code darksirensstat, which is available under open source license at https://github.com/cosmostatgw/darksirensstat. | cosmology with ligo/virgo dark sirens: hubble parameter and modified gravitational wave propagation |
primordial black holes (pbhs) from the early universe have been connected with the nature of dark matter and can significantly affect cosmological history. we show that coincidence dark radiation and density fluctuation gravitational wave signatures associated with evaporation of ≲109 g pbhs can be used to explore and obtain important hints about the formation mechanisms of spinning and non-spinning pbhs spanning orders of magnitude in mass-range, which is challenging to do otherwise. | exploring evaporating primordial black holes with gravitational waves |
dynamical chern-simons (dcs) gravity has been attracting plenty of attentions due to the fact that it is a parity-violating modified theory of gravity that corresponds to a well-posed effective field theory in weak coupling approximation. in particular, a rotating black hole in dcs gravity is in contrast to the general relativistic counterparts. in this paper, we revisit the shadow of analytical rotating black hole spacetime in dcs modified gravity, based on which we study the shadow observables, discuss the constraint on the model parameters from the event horizon telescope (eht) observations, and analyze the real part of quasi-normal modes (qnms) in the eikonal limit. in addition, we explore the deflection angle in weak gravitational field limit with the use of gauss-bonnet theorem. we find that the shadow related physics and the weak gravitational lensing effect are significantly influenced by the cs coupling, which could provide theoretical predictions for a future test of the dcs theory with eht observations. | shadow revisiting and weak gravitational lensing with chern-simons modification |
the first observations of the james webb space telescope (jwst) have identified six massive galaxy candidates with the stellar masses $m_\ast\gtrsim 10^{10}\,m_\odot$ at high redshifts $7.4\lesssim z\lesssim 9.1$, with two most massive high-$z$ objects having the cumulative comoving number densities $n_{\rm g}$ up to $1.6\times 10^{-5}\, {\rm mpc}^{-3}$. the presence of such massive sources in the early universe challenges the standard $\lambda$cdm model since the needed star formation efficiency is unrealistically high. this tension can be alleviated via the accretion of massive primordial black holes (pbhs). in this work, with the updated data from the first jwst observations, we find that the pbhs with mass $10^8\,m_\odot\lesssim m_{\rm pbh}\lesssim 10^{11}\,m_\odot$ can act as the seeds of extremely massive galaxies even with a low abundance $10^{-7}\lesssim f_{\rm pbh}\lesssim 10^{-3}$. we construct an ultraslow-roll inflation model and investigate its possibility of producing the required pbhs. we explore the model in two cases, depending on whether there is a perfect plateau on the inflaton potential. if the plateau is allowed to incline slightly, our model can produce the pbhs that cover the required pbh mass and abundance range to explain the jwst data. | an inflation model for massive primordial black holes to interpret the jwst observations |
the electromagnetic (em) perturbations of the black hole solutions in general relativity coupled to nonlinear electrodynamics (ned) are studied for both electrically and magnetically charged black holes, assuming that the em perturbations do not alter the spacetime geometry. it is shown that the effective potentials of the electrically and magnetically charged black holes related to test perturbative ned em fields are related to the effective metric governing the photon motion, contrary to the effective potential of the linear electrodynamic (maxwell) field that is related to the spacetime metric. consequently, corresponding quasinormal (qn) frequencies differ as well. as a special case, we study new family of the ned black hole solutions which tend in the weak field limit to the maxwell field, giving the reissner-nordström (rn) black hole solution. we compare the ned maxwellian black hole qn spectra with the rn black hole qn spectra. | electromagnetic perturbations of black holes in general relativity coupled to nonlinear electrodynamics |
we present an improved search for binary compact-object mergers using a network of ground-based gravitational-wave detectors. we model a volumetric, isotropic source population and incorporate the resulting distribution over signal amplitude, time delay, and coalescence phase into the ranking of candidate events. we describe an improved modeling of the background distribution, and demonstrate incorporating a prior model of the binary mass distribution in the ranking of candidate events. we find an ∼ 10 % and ∼ 20 % increase in detection volume for simulated binary neutron star and neutron star black hole systems, respectively, corresponding to a reduction of the false alarm rates assigned to signals by between one and two orders of magnitude. | detecting binary compact-object mergers with gravitational waves: understanding and improving the sensitivity of the pycbc search |
superstrata are smooth horizonless microstate geometries for the supersymmetric d1-d5-p black hole in type iib supergravity. in the cft, "superstratum states" are defined to be the component of the supergraviton gas that is obtained by breaking the cft into "|00>-strands" and acting on each strand with the "small," anomaly-free superconformal generators. we show that the recently-constructed supercharged superstrata represent a final and crucial component for the construction of the supergravity dual of a generic superstratum state and how the supergravity solution faithfully represents all the coherent superstratum states of the cft. for the supergravity alone, this shows that generic superstrata do indeed fluctuate as functions of three independent variables. smoothness of the complete supergravity solution also involves "coiffuring constraints" at second-order in the fluctuations and we describe how these lead to new predictions for three-point functions in the dual cft. we use a hybrid of the original and supercharged superstrata to construct families of single-mode superstrata that still have free moduli after one has fixed the asymptotic charges of the system. we also study scalar wave perturbations in a particular family of such solutions and show that the mass gap depends on the free moduli. this can have interesting implications for superstrata at non-zero temperature. | superstratum symbiosis |
a present challenge in testing general relativity (gr) with binary black hole gravitational wave detections is the inability to perform model-dependent tests due to the lack of merger waveforms in beyond-gr theories. in this study, we produce the first numerical relativity binary black hole gravitational waveform in einstein-dilaton-gauss-bonnet (edgb) gravity, a higher-curvature theory of gravity with motivations in string theory. we evolve a binary black hole system in order-reduced edgb gravity, with parameters consistent with gw150914. we focus on the merger portion of the waveform, due to the presence of secular growth in the inspiral phase. we compute mismatches with the corresponding general relativity merger waveform, finding that from a post-inspiral-only analysis, we can constrain the edgb lengthscale to be √{αgb}≲11 km . | numerical relativity simulation of gw150914 in einstein-dilaton-gauss-bonnet gravity |
the agn black hole mass database is a compilation of all published spectroscopic reverberation-mapping studies of active galaxies. we have created a public web interface, where users may get the most up-to-date black hole masses from reverberation mapping for any particular active galactic nucleus (agn), as well as obtain the individual measurements upon which the masses are based and the appropriate references. while the database currently focuses on the measurements necessary for black hole mass determinations, we also plan to expand it in the future to include additional useful information, such as host-galaxy characteristics. new reverberation mapping results will also be incorporated into the database as they are published in peer-refereed journals. | the agn black hole mass database |
the measurement of multiple ringdown modes in gravitational waves from binary black hole mergers will allow for testing the fundamental properties of black holes in general relativity and to constrain modified theories of gravity. to enhance the ability of advanced ligo/virgo to perform such tasks, we propose a coherent mode stacking method to search for a chosen target mode within a collection of multiple merger events. we first rescale each signal so that the target mode in each of them has the same frequency and then sum the waveforms constructively. a crucial element to realize this coherent superposition is to make use of a priori information extracted from the inspiral-merger phase of each event. to illustrate the method, we perform a study with simulated events targeting the ℓ=m =3 ringdown mode of the remnant black holes. we show that this method can significantly boost the signal-to-noise ratio of the collective target mode compared to that of the single loudest event. using current estimates of merger rates, we show that it is likely that advanced-era detectors can measure this collective ringdown mode with one year of coincident data gathered at design sensitivity. | black hole spectroscopy with coherent mode stacking |
the poincaré invariant vacuum is not unique in quantum gravity. the bms supertranslation symmetry originally defined at null infinity is spontaneously broken and results in inequivalent poincaré vacua. in this paper we construct the unique vacua which interpolate between past and future null infinity in bms gauge and which are entirely characterized by an arbitrary goldstone boson defined on the sphere which breaks bms invariance. we show that these vacua contain a defect which carries no poincaré charges but which generically carries superrotation charges. we argue that there is a huge degeneracy of vacua with multiple defects. we also present the single defect vacua with its canonically conjugated source which can be constructed from a liouville boson on the stereographic plane. we show that positivity of the energy forces the stress-tensor of the boson to vanish as a boundary condition. finite superrotations, which turn on the sources, are therefore physically ruled out as canonical transformations around the vacua. yet, infinitesimal superrotations are external symplectic symmetries which are associated with conserved charges which characterize the goldstone boson. | vacua of the gravitational field |
we consider a massive gravity black hole in four-dimensional anti-de sitter space and study the effect of thermal fluctuations on the thermodynamics of the black hole. we consider thermal fluctuations as logarithmic correction terms in the entropy. we analyze the effect of logarithmic correction on thermodynamics potentials like helmholtz and gibbs which are found decreasing functions. we study critical points and stability and find that the presence of logarithmic correction is necessary to have stable phase and critical point. | p -v criticality of first-order entropy corrected ads black holes in massive gravity |
we present a measurement of the hubble constant h0 using the gravitational wave (gw) event gw190814, which resulted from the coalescence of a 23 m⊙ black hole with a 2.6 m⊙ compact object, as a standard siren. no compelling electromagnetic counterpart has been identified for this event; thus our analysis accounts for thousands of potential host galaxies within a statistical framework. the redshift information is obtained from the photometric redshift (photo-z) catalog from the dark energy survey. the luminosity distance is provided by the ligo/virgo gravitational wave sky map. since this gw event has the second-smallest localization volume after gw170817, gw190814 is likely to provide the best constraint on cosmology from a single standard siren without identifying an electromagnetic counterpart. our analysis uses photo-z probability distribution functions and corrects for photo-z biases. we also reanalyze the binary black hole gw170814 within this updated framework. we explore how our findings impact the h0 constraints from gw170817, the only gw merger associated with a unique host galaxy. from a combination of gw190814, gw170814, and gw170817, our analysis yields ${h}_{0}={72.0}_{-8.2}^{+12}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ (68% highest-density interval, hdi) for a prior in h0 uniform between $[20\mathrm{and}140]\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ . the addition of gw190814 and gw170814 to gw170817 improves the 68% hdi from gw170817 alone by ∼18%, showing how well-localized mergers without counterparts can provide a significant contribution to standard siren measurements, provided that a complete galaxy catalog is available at the location of the event. | a statistical standard siren measurement of the hubble constant from the ligo/virgo gravitational wave compact object merger gw190814 and dark energy survey galaxies |
very-long-baseline interferometry (vlbi) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10-100 gravitational radii (rg ≡ gm/c2) scales in nearby sources1. centaurus a is the closest radio-loud source to earth2. it bridges the gap in mass and accretion rate between the supermassive black holes (smbhs) in messier 87 and our galactic centre. a large southern declination of −43° has, however, prevented vlbi imaging of centaurus a below a wavelength of 1 cm thus far. here we show the millimetre vlbi image of the source, which we obtained with the event horizon telescope at 228 ghz. compared with previous observations3, we image the jet of centaurus a at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. we reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. we find that the source structure of centaurus a resembles the jet in messier 87 on ~500 rg scales remarkably well. furthermore, we identify the location of centaurus a's smbh with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source's event horizon shadow4 should be visible at terahertz frequencies. this location further supports the universal scale invariance of black holes over a wide range of masses5,6. | event horizon telescope observations of the jet launching and collimation in centaurus a |
we study the dynamics of a pair of extremal (half-bps) black holes in n = 8 supergravity, as a potentially solvable model of gravitational dynamics. as a diagnosis of hidden symmetries, we ask whether the perihelion of the orbits precesses over time. we consider black hole charge vectors with arbitrary misalignment. first, we use scattering amplitude methods to compute the leading post-newtonian correction for general mass ratios. this computation is greatly simplified by introducing a suitable on-shell superspace. second, we study the probe limit to all orders in velocity and newton's constant through a ten-dimensional brane setup. in all cases we find no precession. we relate this to the absence of scalar triangle integrals. | integrability of black hole orbits in maximal supergravity |
we consider the modified einstein equations obtained in the framework of effective spherically symmetric polymer models inspired by loop quantum gravity. when one takes into account the anomaly free pointwise holonomy quantum corrections, the modification of einstein equations is parametrized by a function f(x) of one phase space variable. we solve explicitly these equations for a static interior black-hole geometry and find the effective metric describing the trapped region, inside the black hole, for any f(x). this general resolution allows to take into account a standard ambiguity inherent to the polymer regularization: namely the choice of the spin j labelling the su(2)-representation of the holonomy corrections. when j=1/2 , the function f(x) is the usual sine function used in the polymer litterature. for this simple case, the effective exterior metric remains the classical schwarzschild's one but acquires modifications inside the hole. the interior metric describes a regular trapped region and presents strong similarities with the reissner-nordström metric, with a new inner horizon generated by quantum effects. we discuss the gluing of our interior solution to the exterior schwarzschild metric and the challenge to extend the solution outside the trapped region due to covariance requirement. by starting from the anomaly free polymer regularization for inhomogeneous spherically symmetric geometry, and then reducing to the homogeneous interior problem, we provide an alternative treatment to existing polymer interior black-hole models which focus directly on the interior geometry, ignoring the covariance issue when introducing the polymer regularization. | polymer schwarzschild black hole: an effective metric |
we consider the gauss-bonnet corrected bardeen black hole solution in 4-d ads space-time. the solution is obtained by the limiting procedure adopted by glavan and lin in 4-d einstein-gauss-bonnet gravity. the general form of first law of black hole thermodynamics is utilized to calculate various thermodynamics variables. the solution exhibit p-v criticality and belong to the universality class of van-der waals fluid. the effect of gauss-bonnet coupling is investigated on critical parameters and inversion temperature. | thermodynamics and p-v criticality of bardeen-ads black hole in 4-d einstein-gauss-bonnet gravity |
we present hα maps at 1 kpc spatial resolution for star-forming galaxies at z ∼ 1, made possible by the wide field camera 3 grism on hubble space telescope (hst). employing this capability over all five 3d-hst/candels fields provides a sample of 3200 galaxies enabling a division into subsamples based on stellar mass and star formation rate (sfr). by creating deep stacked hα images, we reach surface brightness limits of 1 × 10-18 erg s-1 cm-2 arcsec-2, allowing us to map the distribution of ionized gas to ∼10 kpc for typical l* galaxies at this epoch. we find that the spatial extent of the hα distribution increases with stellar mass as {r}{{h}α }=1.5{({m}* /{10}10{m}⊙ )}0.23 kpc. the hα emission is more extended than the stellar continuum emission, consistent with inside-out assembly of galactic disks. this effect grows stronger with mass as {r}{{h}α }/{r}* =1.1 {({m}* /{10}10{m}⊙ )}0.054. we map the hα distribution as a function of sfr(ir+uv) and find evidence for “coherent star formation” across the sfr-m * plane: above the main sequence (ms), hα is enhanced at all radii; below the ms, hα is depressed at all radii. this suggests that at all masses the physical processes driving the enhancement or suppression of star formation act throughout the disks of galaxies. at high masses ({10}10.5\lt {m}* /{m}⊙ \lt {10}11), above the ms, hα is particularly enhanced in the center, potentially building bulges and/or supermassive black holes. below the ms, a strong central dip in the ew(hα), as well as the inferred specific sfr, appears. importantly, though, across the entirety of the sfr-m * plane, the absolute sfr as traced by hα is always centrally peaked, even in galaxies below the ms. | where stars form: inside-out growth and coherent star formation from hst hα maps of 3200 galaxies across the main sequence at 0.7 < z < 1.5 |
i review some recent progresses in counting the number of microstates of ads supersymmetric black holes in dimension equal or greater than four using holography. the counting is obtained by applying localization and matrix model techniques to the dual field theory. i cover in details the case of dyonic ads4 black holes, corresponding to a twisted compactification of the dual field theory, and i discuss the state of the art for rotating ads5 black holes. | ads black holes, holography and localization |
we study the shadow behaviors of five dimensional (5d) black holes embedded in type iib superstring/supergravity inspired spacetimes by considering solutions with and without rotations. geometrical properties as shapes and sizes are analyzed in terms of the d3-brane number and the rotation parameter. concretely, we find that the shapes are indeed significantly distorted by such physical parameters and the size of the shadows decreases with the brane or "color" number and the rotation. then, we investigate geometrical observables and energy emission rate aspects. | shadows of 5d black holes from string theory |
in abbott et al. [phys. rev. x 6, 041014 (2016), 10.1103/physrevx.6.041014], the properties of the first gravitational wave detected by ligo, gw150914, were measured by employing an effective-one-body (eob) model of precessing binary black holes whose underlying dynamics and waveforms were calibrated to numerical-relativity (nr) simulations. here, we perform the first extensive comparison of such an eobnr model to 70 precessing nr waveforms that span mass ratios from 1 to 5, dimensionless spin magnitudes up to 0.5, generic spin orientations, and length of about 20 orbits. we work in the observer's inertial frame and include all ℓ=2 modes in the gravitational-wave polarizations. we introduce new prescriptions for the eob ringdown signal concerning its spectrum and time of onset. for total masses between 10 m⊙ and 200 m⊙ , we find that precessing eobnr waveforms have unfaithfulness within about 3% to nr waveforms when considering the advanced-ligo design noise curve. this result is obtained without recalibration of the inspiral-plunge signal of the underlying nonprecessing eobnr model. the unfaithfulness is computed with maximization over time and phase of arrival, sky location, and polarization of the eobnr waveform, and it is averaged over sky location and polarization of the nr signal. we also present comparisons between nr and eobnr waveforms in a frame that tracks the orbital precession. | validating the effective-one-body model of spinning, precessing binary black holes against numerical relativity |
for primordial perturbations, deviations from gaussian statistics on the tail of the probability distribution can be associated with non-perturbative effects of inflation. in this paper, we present some particular examples in which the tail of the distribution becomes highly non-gaussian although the statistics remains almost gaussian in the perturbative regime. we begin with an extension of the ultra-slow-roll inflation that incorporates a transition process, where the inflaton climbs up a tiny potential step at the end of the non-attractor stage before it converges to the slow-roll attractor. through this example, we identify the key role of the off-attractor behaviour for the upward-step transition, and then extend the analysis to another type of the transition with two slow-roll stages connected by a tiny step. we perform both the perturbative and non-perturbative analyses of primordial fluctuations generated around the step in detail, and show that the tiny but nontrivial transition may affect large perturbations in the tail of the distribution, while the perturbative non-gaussianity remains small. our result indicates that the non-gaussian tails can have rich phenomenology which has been overlooked in conventional analyses. we also study the implications of this non-gaussian tail for the formation of primordial black holes, and find that their mass fraction can be parametrically amplified by several orders of magnitudes in comparison with the case of the gaussian distribution. additionally, we also discuss a mechanism of primordial black holes formation for this upward step inflation model by trapping the inflaton in the bottom of the step. | highly non-gaussian tails and primordial black holes from single-field inflation |
despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. none of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. design principles for fullerene-free acceptors remain unclear in the field. here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. we achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. this study describes a new motif for designing highly efficient acceptors for organic solar cells. | molecular helices as electron acceptors in high-performance bulk heterojunction solar cells |
we use the classical double copy to identify a necessary condition for maxwell theory sources to constitute single copies of kerr-schild solutions to einstein's equations. in the case of four-dimensional kerr-schild spacetimes on minkowski backgrounds, we extend this condition to a parameterization of the corresponding single copies. these are given by líenard-wiechert fields of charges on complex worldlines. this unifies the known instances of the kerr-schild double copy black holes on flat four-dimensional backgrounds into a single framework. furthermore, we use the more generic condition identified to show why the black ring in five dimensions does not admit kerr-schild coordinates. | kerr-schild double copy and complex worldlines |
we present a d-dimensional bardeen like anti-de sitter (ads) black hole solution in einstein-gauss-bonnet (egb) gravity, viz., bardeen-egb-ads black holes. the bardeen-egb-ads black hole has an additional parameter due to magnetic charge ( e), apart from mass ( m) and gauss-bonnet parameter (α ). interestingly, for each value of α , there exist a critical e = e_e which corresponds to an extremal regular black hole with degenerate horizons, while for e< e_e, it describes non-extremal black hole with two horizons. despite the complicated solution, the thermodynamical quantities, like temperature ( t), specific heat( c) and entropy ( s) associated with the black hole are obtained exactly. it turns out that the heat capacity diverges at critical horizon radius r_+ = r_c, where the temperature attains maximum value and the hawking-page transition is achievable. thus, we have an exact d-dimensional regular black holes, when evaporates lead to a thermodynamical stable remnant. | d-dimensional bardeen-ads black holes in einstein-gauss-bonnet theory |
we search for signatures of gravitational lensing in the binary black hole events detected by advanced ligo and virgo during their first two observational runs. in particular, we look for three effects: (1) evidence of lensing magnification in the individual signals due to galaxy lenses, (2) evidence of multiple images due to strong lensing by galaxies, and (3) evidence of wave optics effects due to point-mass lens. we find no compelling evidence of any of these signatures in the observed gravitational wave signals. however, as the sensitivities of gravitational wave detectors improve in the future, detecting lensed events may become quite likely. | search for gravitational lensing signatures in ligo-virgo binary black hole events |
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