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according to the no-hair theorem, static black holes are described by a schwarzschild spacetime provided there are no other sources of the gravitational field. this requirement, however, is in astrophysical realistic scenarios often violated, e.g., if the black hole is part of a binary system or if it is surrounded by an accretion disk. in these cases, the black hole is distorted due to tidal forces. nonetheless, the subsequent formulation of the no-hair theorem holds: the contribution of the distorted black hole to the multipole moments that describe the gravitational field close to infinity and, thus, all sources is that of a schwarzschild black hole. it still has no hair. this implies that there is no multipole moment induced in the black hole and that its second love numbers, which measure some aspects of the distortion, vanish as was already shown in approximations to general relativity. but here we prove this property for astrophysical relevant black holes in full general relativity. | no-hair theorem for black holes in astrophysical environments |
it remains unclear in general how the pole skipping appears as a physical phenomenon, and we study the issue in the context of the anti-de sitter soliton. the pole skipping has been discussed in black hole backgrounds, but the pole skipping occurs even in the anti-de sitter soliton background. the geometry has a compact s1 direction, and we compute the mass spectrum for the bulk scalar field, the bulk maxwell field, and the gravitational perturbations with s1 momentum. we show that the pole skipping leaves its fingerprint in the normal mode spectrum. the spectrum has some puzzling features because the wouldbe states are missing at pole-skipping points. the puzzling features disappear once one takes into account these pole-skipping points that we call "missing states." | pole skipping as missing states |
we construct a multiverse model based on a recent proposal for ds wedge holography, where empty ads$_3$ space is cut off by a pair of accelerated ds$_2$ space universes, one near the ads boundary, denoted the uv brane, and one in the ads interior, the ir brane. we glue together several copies of this configuration along the uv and ir branes in a periodic matter. to provide the model with dynamics of the like near nariai black holes used in other multiverse toy models, we add ds jt gravity as an intrinsic gravity theory on the ir branes. we then study the entanglement entropy with respect to a uv brane observer, who finds a page curve transition due to an entanglement island connecting the uv and ir branes. this process involves the coarse-graining of information outside the causally accessible region to the observer. our model provides an explicit realization of entanglement between ir and uv degrees of freedom encoded in the multiverse. | a multiverse model in ds wedge holography |
in this review, we provide an up-to-date account of quantitative holographic descriptions of the strongly coupled quark-gluon plasma (qgp) produced in heavy-ion collisions, based on the class of gauge-gravity einstein-maxwell-dilaton (emd) models. holography is employed to tentatively map the qcd phase diagram at finite temperature onto a dual theory of charged, asymptotically ads black holes in 5d. with a quantitative focus on the hot qcd phase diagram, the emd models reviewed are adjusted to describe lattice results for the finite-temperature qcd equation of state, with 2+1 flavors and physical quark masses, at zero chemical potential and vanishing electromagnetic fields. the predictive power of emd models is tested by quantitatively comparing their predictions for the hot qcd equation of state at nonzero baryon density and the corresponding state-of-the-art lattice qcd results. the shear and bulk viscosities predicted by these emd models are also compared to the corresponding profiles favored by the latest phenomenological multistage models describing different heavy-ion data. we report preliminary results from a bayesian analysis which provide systematic evidence that lattice results at finite temperature and zero baryon density strongly constrains the free parameters of emd models. remarkably, the set of parameters constrained by lattice results at zero chemical potential produces emd models in quantitative agreement with lattice qcd results also at finite baryon density. we also review results for equilibrium and transport properties from magnetic emd models, describing the qgp at finite temperatures and magnetic fields. finally, we provide a critical assessment of the main limitations and drawbacks of the holographic models reviewed in the present work, and point out some perspectives we believe are of fundamental importance for future developments. | hot qcd phase diagram from holographic einstein-maxwell-dilaton models |
we study the eft of a spinning compact object and show that with appropriate gauge fixing, computations become amenable to worldline quantum field theory techniques. we use the resulting action to compute compton and one-loop scattering amplitudes at fourth order in spin. by matching these amplitdes to solutions of the teukolsky equations, we fix the values of wilson coefficients appearing in the eft such that it reproduces kerr black hole scattering. we keep track of the spin supplementary condition throughout our computations and discuss alternative ways to ensure its preservation. | scattering of spinning compact objects from a worldline eft |
we investigate the effects of quintessence dark energy on the shadows of black hole, surrounded by various profiles of accretions. for the thin-disk accretion, the images of the black hole comprises the dark region and bright region, including direct emission, lensing rings and photon rings. although their details depend on the form of the emission, generically, direct emission plays a major role for the observed brightness of the black hole, while the lensing ring makes a small contribution and the photon ring makes a negligible contribution. the existence of a cosmological horizon also plays an important role in the shadows, since the observer in the domain of outer communications is near the cosmological horizon. for spherically symmetric accretion, static and infalling matters are considered. we find that the positions of photon spheres are the same for both static and infalling accretions. however, the observed specific intensity of the image for infalling accretion is darker than for static accretion, due to the doppler effect of the infalling motion. | influence of quintessence dark energy on the shadow of black hole |
a four-dimensional regularization of lovelock-lanczos gravity up to an arbitrary curvature order is considered. we show that lovelock-lanczos terms can provide a non-trivial contribution to the einstein field equations in four dimensions, for spherically symmetric and friedmann-lemaître-robertson-walker spacetimes, as well as at first order in perturbation theory around (anti) de sitter vacua. we will discuss the cosmological and black hole solutions arising from these theories, focusing on the presence of attractors and their stability. although curvature singularities persist for any finite number of lovelock terms, it is shown that they disappear in the non-perturbative limit of a theory with a unique vacuum. | regularized lovelock gravity |
the gravitational potential of initially poisson distributed primordial black holes (pbh) can induce a stochastic gravitational-wave background (sgwb) at second order in cosmological perturbation theory. this sgwb was previously studied in the context of general relativity (gr) and modified gravity setups by assuming a monochromatic pbh mass function. here we extend the previous analysis in the context of gr by studying the aforementioned sgwb within more physically realistic regimes where pbhs have different masses. in particular, starting from a power-law cosmologically motivated primordial curvature power spectrum with a running spectral index we extract the extended pbh mass function and the associated to it pbh gravitational potential which acts as the source of the scalar induced sgwb. at the end, by taking into account the dynamical evolution of the pbh gravitational potential during the transition from the matter era driven by pbhs to the radiation era we extract the respective gw signal today. interestingly, in order to trigger an early pbh-dominated era and avoid the gw constraints at bbn we find that the running of the spectral index αs of our primordial curvature power spectrum should be within the narrow range αs ⋲ [3.316,3.355] × 10-3 while at the same time the gw signal is found to be potentially detectable by lisa. | gravitational waves induced from primordial black hole fluctuations: the effect of an extended mass function |
we derive formulas for the leading mass, entropy, and long-range self-force corrections to extremal black holes due to higher-derivative operators. these formulas hold for black holes with arbitrary couplings to gauge fields and moduli, provided that the leading-order solutions are static, spherically-symmetric, extremal, and have nonzero horizon area. to use these formulas, both the leading-order black hole solution and the higher-derivative effective action must be known, but there is no need to solve the derivative-corrected equations of motion. we demonstrate that the mass, entropy and self-force corrections involve linearly-independent combinations of the higher-derivative couplings at any given point in the moduli space, and comment on their relations to various swampland conjectures. | derivative corrections to extremal black holes with moduli |
gw190521 is a short-duration, low-frequency gravitational-wave signal in the ligo-virgo catalogue. the signal is consistent with the ringdown and possibly some of the inspiral-merger of an intermediate-mass binary black-hole coalescence. we find that previous models of the quasinormal mode spectrum in the ringdown of gw190521 give remnant mass and spin estimates which are not fully consistent with those of many inspiral-merger-ringdown waveforms. in our own analysis, we find that ringdown models which include both the angular l =2 , m =1 and l =m =2 fundamental quasinormal modes are in full agreement with most inspiral-merger-ringdown waveforms, and in particular with the numerical relativity surrogate nrsur7dq4. we also find some support for including the l =3 , m =2 fundamental quasinormal mode in our fits, building on capano et al.'s findings regarding a higher-frequency subdominant mode. we propose an interpretation of our gw190521 ringdown model that links precession to the excitation of l ≠m quasinormal modes, but we do not rule out eccentricity or other interpretations. | ringdown of gw190521: hints of multiple quasinormal modes with a precessional interpretation |
computing the 4d euclidean path integral to one-loop order we find the large quantum corrections that govern the behavior of a spherically symmetric non-supersymmetric near-extremal black hole at very low temperature. these corrections appear from the near-horizon geometry of the near-extremal black hole. using first-order perturbation theory we find that such corrections arise from the zero modes of the extremal background. in the logarithm of the partition function, these correspond to terms involving logarithm of temperature. part of our result matches with the existing one in literature derived from an effective schwarzian theory. | revisiting leading quantum corrections to near extremal black hole thermodynamics |
we study the open quantum dynamics of the sachdev-ye-kitaev (syk) model described by the lindblad master equation, where the syk model is coupled to markovian reservoirs with jump operators that are either linear or quadratic in the majorana fermion operators. of particular interest for us is the time evolution of the dissipative form factor, which quantifies the average overlap between the initial and time-evolved density matrices as an open quantum generalization of the loschmidt echo. we find that the dissipative form factor exhibits dynamical quantum phase transitions. we analytically demonstrate a discontinuous dynamical phase transition in the limit of a large number of fermion flavors, which is formally akin to the thermal phase transition in the two-coupled syk model between the black-hole and wormhole phases. we also find continuous dynamical phase transitions that do not have counterparts in the two-coupled syk model. while the phase transitions are sharp in the limit of a large number of fermion flavors, their qualitative signatures are present even for a finite number of fermion flavors, as we show numerically. | dynamical quantum phase transitions in sachdev-ye-kitaev lindbladians |
we study the nonlinear dynamics of axion inflation, capturing for the first time the inhomogeneity and full dynamical range during strong backreaction, till the end of inflation. accounting for inhomogeneous effects leads to a number of new relevant results, compared to spatially homogeneous studies: (i) the number of extra efoldings beyond slow-roll inflation increases very rapidly with the coupling, (ii) oscillations of the inflaton velocity are attenuated, (iii) the tachyonic gauge field helicity spectrum is smoothed out (i.e., the spectral oscillatory features disappear), broadened, and shifted to smaller scales, and (iv) the nontachyonic helicity is excited, reducing the chiral asymmetry, now scale dependent. our results are expected to impact strongly on the phenomenology and observability of axion inflation, including gravitational wave generation and primordial black hole production. | strong backreaction regime in axion inflation |
we match scattering amplitudes in point particle effective field theory (eft) and general relativity to extract low frequency dynamical tidal responses of rotating (kerr) black holes to all orders in spin. in the conservative sector, we study local worldline couplings that correspond to the time-derivative expansion of the black hole tidal response function. these are dynamical (frequency-dependent) generalizations of the static love numbers. we identify and extract couplings of three types of subleading local worldline operators: the curvature time derivative terms, the spin - curvature time derivative couplings, and quadrupole - octupole mixing operators that arise due to the violation of spherical symmetry. the first two subleading couplings are non-zero and exhibit a classical renormalization group running; we explicitly present their scheme-independent beta functions. the conservative mixing terms, however, vanish as a consequence of vanishing static love numbers. in the non-conservative sector, we match the dissipation numbers at next-to-leading and next-to-next-to leading orders in frequency. in passing, we identify terms in the general relativity absorption probabilities that originate from tails and short-scale logarithmic corrections to the lowest order dissipation contributions. | dynamical tidal response of kerr black holes from scattering amplitudes |
in this paper, we investigate the topological number of de-sitter black hole solutions with different charges (q) and rotational (a) parameters. by using generalized free energy and duan's ϕ -mapping topological current theory, we find that the topological numbers of black holes can still be classified into three types. in addition, we interestingly found the topological classes for de-sitter (ds) spacetime with distinct horizons, i.e., black hole event horizon and cosmological horizon, will be different. moreover, we also investigate topological classifications of ds black hole solutions in higher dimensions with or without the gauss-bonnet term. | topological classes of black holes in de-sitter spacetime |
we show that, whenever the perturbations of some field are excited during inflation by a physical process on sub-horizon scales, they unavoidably generate, even through gravitational interactions alone, a significant resonant ir cascade of power down to scales that are of the order of the horizon at that time (we denote these scales as near ir). we provide general analytic one-loop results for the enhancement of the ir power of the curvature perturbation generated by this effect, highlighting the role played by the resonance. we then study a number of examples in which the excited state is: (i) an isocurvature field, (ii) the curvature perturbation itself, (iii) a mixture of curvature and isocurvature fluctuations driven to an excited state by their coupled dynamics. in the cases shown, the cascade significantly modifies the near ir part of the power spectrum of the curvature perturbation with respect to the linear theory, indicating that this effect can impact the phenomenology associated with a variety of mechanisms considered in the literature, notably concerning primordial black holes and gravitational waves. | one-loop infrared rescattering by enhanced scalar fluctuations during inflation |
this is the first of several short notes in which i will describe phenomena that illustrate gr=qm. in it i explain that the gravitational attraction that a black hole exerts on a nearby test object is a consequence of a fundamental law of quantum mechanics---the tendency for complexity to grow. it will also be shown that the einstein bound on velocities is closely related to the quantum-chaos bound of maldacena, shenker, and stanford. | why do things fall? |
we address a long-standing problem of describing the thermodynamics of an accelerating black hole. we derive a standard first law of black hole thermodynamics, with the usual identification of entropy proportional to the area of the event horizon—even though the event horizon contains a conical singularity. this result not only extends the applicability of black hole thermodynamics to realms previously not anticipated, it also opens a possibility for studying novel properties of an important class of exact radiative solutions of einstein equations describing accelerated objects. we discuss the thermodynamic volume, stability, and phase structure of these black holes. | thermodynamics of accelerating black holes |
the island rule for the entanglement entropy is applied to an eternal reissner-nordström black hole. the key ingredient is that the black hole is assumed to be in thermal equilibrium with a heat bath of an arbitrary temperature and so the generalized entropy is treated as being off-shell. taking the on-shell condition to the off-shell generalized entropy, we find the generalized entropy and then obtain the entanglement entropy following the island rule. for the non-extremal black hole, the entanglement entropy grows linearly in time and can be saturated after the page time as expected. the entanglement entropy also has a well-defined schwarzschild limit. in the extremal black hole, the island prescription provides a logarithmically growing entanglement entropy in time and a constant entanglement entropy after the page time. in the extremal black hole, the boundary of the island hits the curvature singularity where the semi-classical approximations appear invalid. to avoid encountering the curvature singularity, we apply this procedure to the hayward black hole regular at the origin. consequently, the presence of the island in extremal black holes can provide a finite entanglement entropy, which might imply non-trivial vacuum configurations of extremal black holes. | entanglement entropy of asymptotically flat non-extremal and extremal black holes with an island |
certain closed-universe big-bang/big-crunch cosmological spacetimes may be obtained by analytic continuation from asymptotically ads euclidean wormholes, as emphasized by maldacena and maoz. we investigate how these euclidean wormhole spacetimes and their associated cosmological physics might be described within the context of ads/cft. we point out that a holographic model for cosmology proposed recently in arxiv:1810.10601 can be understood as a specific example of this picture. based on this example, we suggest key features that should be present in more general examples of this approach to cosmology. the basic picture is that we start with two non-interacting copies of a euclidean holographic cft associated with the asymptotic regions of the euclidean wormhole and couple these to auxiliary degrees of freedom such that the original theories interact strongly in the ir but softly in the uv. the partition function for the full theory with the auxiliary degrees of freedom can be viewed as a product of partition functions for the original theories averaged over an ensemble of possible sources. the lorentzian cosmological spacetime is encoded in a wavefunction of the universe that lives in the hilbert space of the auxiliary degrees of freedom. | comments on wormholes, ensembles, and cosmology |
this article reviews the progress in our understanding of the reconstruction of the bulk spacetime in the holographic correspondence from the dual field theory including an account of how these developments have led to the reproduction of the page curve of the hawking radiation from black holes. we review quantum error correction and relevant recovery maps with toy examples based on tensor networks, and discuss how it provides the desired framework for bulk reconstruction in which apparent inconsistencies with properties of the operator algebra in the dual field theory are naturally resolved. the importance of understanding the modular flow in the dual field theory has been emphasized. we discuss how the state-dependence of reconstruction of black hole microstates can be formulated in the framework of quantum error correction with inputs from extremal surfaces along with a quantification of the complexity of encoding of bulk operators. finally, we motivate and discuss a class of tractable microstate models of black holes which can illuminate how the black hole complementarity principle can emerge operationally without encountering information paradoxes, and provide new insights into generation of desirable features of encoding into the hawking radiation. | holographic spacetime, black holes and quantum error correcting codes: a review |
the open question of whether a black hole can become tidally deformed by an external gravitational field has profound implications for fundamental physics, astrophysics, and gravitational-wave astronomy. love tensors characterize the tidal deformability of compact objects such as astrophysical (kerr) black holes under an external static tidal field. we prove that all love tensors vanish identically for a kerr black hole in the nonspinning limit or for an axisymmetric tidal perturbation. in contrast to this result, we show that love tensors are generically nonzero for a spinning black hole. specifically, to linear order in the kerr black hole spin and the weak perturbing tidal field, we compute in closed form the love tensors that couple the mass-type and current-type quadrupole moments to the electric-type and magnetic-type quadrupolar tidal fields. for a dimensionless spin ∼0.1 , the nonvanishing quadrupolar love tensors are ∼2 ×10-3, thus showing that black holes are particularly "rigid" compact objects. | spinning black holes fall in love |
in this note we study the $1+1$ dimensional jackiw-teitelboim gravity in lorentzian signature, explicitly constructing the gauge-invariant classical phase space and the quantum hilbert space and hamiltonian. we also semiclassically compute the hartle-hawking wave function in two different bases of this hilbert space. we then use these results to illustrate the gravitational version of the factorization problem of ads/cft: the hilbert space of the two-boundary system tensor-factorizes on the cft side, which appears to be in tension with the existence of gauge constraints in the bulk. in this model the tension is acute: we argue that jt gravity is a sensible quantum theory, based on a well-defined lorentzian bulk path integral, which has no cft dual. in bulk language, it has wormholes but it does not have black hole microstates. it does however give some hint as to what could be added to to rectify these issues, and we give an example of how this works using the syk model. finally we suggest that similar comments should apply to pure einstein gravity in $2+1$ dimensions, which we'd then conclude also cannot have a cft dual, consistent with the results of maloney and witten. | the factorization problem in jackiw-teitelboim gravity |
very recently, it was suggested that combining the swampland program with the smallness of the dark energy and confronting these ideas to experiment lead to the prediction of the existence of a single extra dimension (dubbed the dark dimension) with characteristic length scale in the micron range. we show that the rate of hawking radiation slows down for black holes perceiving the dark dimension and discuss the impact of our findings in assessing the dark matter fraction that could be composed of primordial black holes. we demonstrate that for a species scale of o (1010 gev ), an all-dark-matter interpretation in terms of primordial black holes should be feasible for masses in the range 1014≲mbh/g ≲1021. this range is extended compared to that in the 4d theory by 3 orders of magnitude in the low mass region. we also show that primordial black holes with mbh∼1012 g could potentially explain the well-known galactic 511 kev gamma-ray line if they make up a tiny fraction of the total dark matter density. | dark dimension, the swampland, and the dark matter fraction composed of primordial black holes |
the newman-janis (nj) algorithm has been extensively used in the literature to generate rotating black hole solutions from nonrotating seed spacetimes. in this work, we show, using various constants of motion, that the null geodesic equations in an arbitrary stationary and axially symmetric rotating spacetime obtained through the nj algorithm can be separated completely, provided that the algorithm is applied successfully without any inconsistency. using the separated null geodesic equations, we then obtain an analytic general formula for obtaining the contour of a shadow cast by a compact object whose gravitational field is given by the arbitrary rotating spacetime under consideration. as special cases, we apply our general analytic formula to some known black holes and reproduce the corresponding results for black hole shadow. finally, we consider a new example and study shadow using our analytic general formula. | black hole shadow in a general rotating spacetime obtained through newman-janis algorithm |
in black hole thermodynamics, it has been observed that ads black holes behave as van der waals system if one interprets the cosmological constant as a pressure term. also the critical exponents for the phase transition of ads black holes and the van der waals systems are same. till now this type of analysis is done by two steps. in the first step one shows that a particular metric allows phase transition and in the second step, using this information, one calculates the exponents. here, we present a different approach based on two universal inputs (the general forms of the smarr formula and the first law of thermodynamics) and one assumption regarding the existence of van der waals like critical point for a metric. we find that the same values of the critical exponents can be obtained by this approach. thus we demonstrate that, though the existence of van der waals like phase transition depends on specific metrics, the values of critical exponents are then fixed for that set of metrics. | p-v criticality of ads black holes in a general framework |
we report atacama large millimeter/submillimeter array (alma) observations of co(3-2) emission in a sample of seven seyfert/liner galaxies at the unprecedented spatial resolution of 0.″1 = 4-8 pc. our aim is to explore the close environment of active galactic nuclei (agn), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. the selected galaxies host low-luminosity agn and have a wide range of activity types (seyferts 1 to 2, liners), and barred or ringed morphologies. the observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. we call these structures molecular tori, even though they often appear as disks without holes in the center. they have varying orientations along the line of sight, unaligned with the host galaxy orientation. the radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 107 to 3.9 × 107 m⊙. the most edge-on orientations of the torus correspond to obscured seyferts. in only one case (ngc 1365), the agn is centered on the central gas hole of the torus. on a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale that play the role of a reservoir to fuel the nucleus. in some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. more frequently, the torus and the agn are slightly off-centered with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10 pc amplitude around the center of mass of the galaxy. our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. by fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge. in some cases, agn feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article. based on observations carried out with alma in cycles 3 and 4. | alma observations of molecular tori around massive black holes |
in this paper we prove integrated energy and pointwise decay estimates for solutions of the vacuum linearized einstein equation on the domain of outer communication of the kerr black hole spacetime. the estimates are valid for the full subextreme range of kerr black holes, provided integrated energy estimates for the teukolsky master equation holds. for slowly rotating kerr backgrounds, such estimates are known to hold, due to the work of one of the authors. the results in this paper thus provide the first stability results for linearized gravity on the kerr background, in the slowly rotating case, and reduce the linearized stability problem for the full subextreme range to proving integrated energy estimates for the teukolsky equation. this constitutes an essential step towards a proof of the black hole stability conjecture, i.e. the statement that the kerr family is dynamically stable, one of the central open problems in general relativity. | stability for linearized gravity on the kerr spacetime |
we investigate the validity of the generalized second law of thermodynamics, applying barrow entropy for the horizon entropy. the former arises from the fact that the black-hole surface may be deformed due to quantum-gravitational effects, quantified by a new exponent δ . we calculate the entropy time-variation in a universe filled with the matter and dark energy fluids, as well as the corresponding quantity for the apparent horizon. we show that although in the case δ =0 , which corresponds to usual entropy, the sum of the entropy enclosed by the apparent horizon plus the entropy of the horizon itself is always a non-decreasing function of time and thus the generalized second law of thermodynamics is valid, in the case of barrow entropy this is not true anymore, and the generalized second law of thermodynamics may be violated, depending on the universe evolution. hence, in order not to have violation, the deformation from standard bekenstein-hawking expression should be small as expected. | the generalized second law of thermodynamics with barrow entropy |
we recently presented a new mechanism for primordial black hole formation during a first-order phase transition in the early universe, which relies on the build-up of particles which are predominantly reflected from the advancing bubble wall. in this companion paper we provide details of the supporting numerical calculations. after describing the general mechanism, we discuss the criteria that need to be satisfied for a black hole to form. we then set out the boltzmann equation that describes the evolution of the relevant phase space distribution function, carefully describing our treatment of the liouville operator and the collision term. finally, we show that black holes will form for a wide range of parameters. | detailed calculation of primordial black hole formation during first-order cosmological phase transitions |
the scalarization of reissner-nordström black holes was recently proposed in the einstein-maxwell-scalar theory. here, we show that the appearance of the scalarized reissner-nordström black hole is closely related to the gregory-laflamme instability of the reissner-nordström black hole without scalar hair. | instability of reissner-nordström black hole in einstein-maxwell-scalar theory |
we study the influence of parameter α on the optical features of schwarzschild-mog black holes with different thin accretions in scalar-tensor-vector gravity. as α increases from 0, the radii of the event horizon, photon sphere, and observed shadow increase in comparison with the schwarzschild black hole. we constrain the parameter α with the experimental data reported by the event horizon telescope collaboration for m87∗ and sagittarius a∗. in the situation of spherical accretions, we unveil that the parameter α has a positive effect on the shadow size but a negative effect on the observed specific intensities. considering that the schwarzschild-mog black hole is surrounded by an optical and geometrically thin accretion disk, we find that the total observed specific intensities are mainly contributed by the direct emissions, while the photon rings and lensed rings provide small contributions. it is also found that with the increase of α , the black hole shadow expands, the photon rings and lensed rings become larger and thicker. besides, we emphasize that the boundary of the observed shadow cast by the aim black hole in the disk accretion scenario is determined by the direct emissions rather than the photon ring emissions. consequently, we unveil that there is a linear relationship involving the critical impact parameter and the starting point of the direct emissions. this finding helps to use the experimental results of the event horizon telescope to infer the critical impact parameter and to test general relativity. | observational signatures of schwarzschild-mog black holes in scalar-tensor-vector gravity: shadows and rings with different accretions |
in this work, we explored the effect of the fuzzy dark matter (fdm) (or wave dark matter) halo on a supermassive black hole (smbh). such a dark matter introduces a soliton core density profile, and we treat it ideally as a spherical distribution that surrounds the smbh located at its center. in this direction, we obtained a new metric due to the union of the black hole and dark matter spacetime geometries. we applied the solution to the two known smbh - sgr. a* and m87* and used the empirical data for the shadow diameter by eht to constrain the soliton core radius given some values of the boson mass . then, we examine the behavior of the shadow radius based on such constraints and relative to a static observer. we found that different shadow sizes are perceived at regions and , and the deviation is greater for values ev. concerning the shadow behavior, we have also analyzed the effect of the soliton profile on the thin-accretion disk. soliton dark matter effects manifest through the varying luminosity near the event horizon. we also analyzed the weak deflection angle and the produced einstein rings due to soliton effects. we found considerable deviation, better than the shadow size deviation, for the light source near the smbh with impact parameters comparable to the soliton core. our results suggest the possible experimental detection of soliton dark matter effects using an smbh at the galactic centers.in this work, the authors explored the effect of the fuzzy dark matter (fdm) (or wave dark matter) halo on a supermassive black hole (smbh). such a dark matter introduces a soliton core density profile, and one treats it ideally as a spherical distribution surrounding the smbh located at its center. in this direction, a new metric was obtained due to the union of the black hole and dark matter spacetime geometries. here the solutions are applied to the two known smbh - sgr. a* and m87* and the empirical data are used for the shadow diameter by eht to constrain the soliton core radius rc given some values of the boson mass mb. then, the behavior of the shadow radius is examined based on such constraints and relative to a static observer. it is found that different shadow sizes are perceived at regions robs < rc and robs > rc, and the deviation is greater for values mb < 10−22 ev. concerning the shadow behavior the effects of the soliton profile on the thin-accretion disk are also analyzed. soliton dark matter effects manifest through the varying luminosity near the event horizon. the investigation of the weak deflection angle and the produced einstein rings due to soliton effects results in considerable deviation, better than the shadow size deviation, for the light source near the smbh with impact parameters comparable to the soliton core. the results suggest the possible experimental detection of soliton dark matter effects using an smbh at the galactic centers. | black hole in quantum wave dark matter |
in this work we present the first calculation of the gravitational self-force on generic bound geodesics in kerr spacetime to first order in the mass ratio. that is, the local correction to equations of motion for a compact object orbiting a larger rotating black hole due to its own impact on the gravitational field. this includes both dissipative and conservative effects. our method builds on and extends earlier methods for calculating the gravitational self-force on equatorial orbits. in particular we reconstruct the local metric perturbation in the outgoing radiation gauge from the weyl scalar ψ4 , which in turn is obtained by solving the teukolsky equation using semianalytical frequency domain methods. the gravitational self-force is subsequently obtained using (spherical) l -mode regularization. we test our implementation by comparing the large l -behavior against the analytically known regularization parameters. in addition we validate our results by comparing the long-term average changes to the energy, angular momentum, and carter constant to changes to these constants of motion inferred from the gravitational wave flux to infinity and down the horizon. | gravitational self-force on generic bound geodesics in kerr spacetime |
the recent direct observation of gravitational waves (gw) from merging black holes opens up the possibility of exploring the theory of gravity in the strong regime at an unprecedented level. it is therefore interesting to explore which extensions to general relativity (gr) could be detected. we construct an effective field theory (eft) satisfying the following requirements. it is testable with gw observations; it is consistent with other experiments, including short distance tests of gr; it agrees with widely accepted principles of physics, such as locality, causality and unitarity; and it does not involve new light degrees of freedom. the most general theory satisfying these requirements corresponds to adding to the gr lagrangian operators constructed out of powers of the riemann tensor, suppressed by a scale comparable to the curvature of the observed merging binaries. the presence of these operators modifies the gravitational potential between the compact objects, as well as their effective mass and current quadrupoles, ultimately correcting the waveform of the emitted gw. | an effective formalism for testing extensions to general relativity with gravitational waves |
higher-dimensional theories admit astrophysical objects like supermassive black holes, which are rather different from standard ones, and their gravitational lensing features deviate from general relativity. it is well known that a black hole shadow is a dark region due to the falling geodesics of photons into the black hole and, if detected, a black hole shadow could be used to determine which theory of gravity is consistent with observations. measurements of the shadow sizes around the black holes can help to evaluate various parameters of the black hole metric. we study the shapes of the shadow cast by the rotating five-dimensional charged einstein-maxwell-chern-simons (emcs) black holes, which is characterized by four parameters, i.e., mass, two spins, and charge, in which the spin parameters are set equal. we integrate the null geodesic equations and derive an analytical formula for the shadow of the five-dimensional emcs black hole, in turn, to show that size of black hole shadow is affected due to charge as well as spin. the shadow is a dark zone covered by a deformed circle, and the size of the shadow decreases with an increase in the charge q when compared with the five-dimensional myers-perry black hole. interestingly, the distortion increases with charge q. the effect of these parameters on the shape and size of the naked singularity shadow of the five-dimensional emcs black hole is also discussed. | shadows of rotating five-dimensional charged emcs black holes |
non-linear interaction between the electromagnetic fields (emf) occurs when vacuum polarization in quantum electrodynamics (qed) happens. the field of non-linear electrodynamics, which may result from this interaction, could have important effects on black hole physics. this paper considers the asymptotically flat black hole solution in einstein-nonlinear electrodynamics (nle) fields. we study the effect of the nle parameters on the black hole deflection angle using the gauss-bonnet theorem in weak field limits, shadow cast using the null geodesics method, and thin accretion disk using the novikov-thorne model. in particular, we studied the time-averaged energy flux, the disk temperature, the differential luminosity, the different emission profiles, and infalling spherical accretion. then we show how the physical quantities depend on β and c parameters of nle and provide some constraints on the nle parameters using the observations of m87* and sgr a* from eht. | probing a non-linear electrodynamics black hole with thin accretion disk, shadow, and deflection angle with m87* and sgr a* from eht |
in the recent paper [phys. rev. lett. 129, 191101 (2022)], the black holes were viewed as topological thermodynamic defects by using the generalized off-shell free energy. their work indicates that all black hole solutions in the pure einstein-maxwell gravity theory could be classified into three different topological classes for four and higher spacetime dimensions. in this paper, we investigate the topological number of btz black holes with different charges $(q)$ and rotational $(j)$ parameters. by using generalized free energy and duan's $\phi$-mapping topological current theory, we interestingly found only two topological classes for btz spacetime. particularly, for $q=j=0$ btz black hole, there has only one zero point and therefore the total topological number is 1. while for rotating or charged cases, there are always two zero points and the global topological number is zero. | topological classes of btz black holes |
quasi-periodic eruptions (qpes) are very-high-amplitude bursts of x-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. it is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. here we report observations of qpes in two further galaxies, obtained with a blind and systematic search of half of the x-ray sky. the optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. indeed, the periods, amplitudes and profiles of the qpes reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5-9. instead, qpes might be driven by an orbiting compact object. furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future x-ray observations may constrain possible changes in their period owing to orbital evolution. this model could make qpes a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11-13, with considerable implications for multi-messenger astrophysics and cosmology14,15. | x-ray quasi-periodic eruptions from two previously quiescent galaxies |
following a new microlensing constraint on primordial black holes (pbhs) with ∼1 020- 1 028 g [h. niikura et al., arxiv:1701.02151.], we revisit the idea of pbh as all dark matter (dm). we have shown that the updated observational constraints suggest the viable mass function for pbhs as all dm to have a peak at ≃1 020 g with a small width σ ≲0.1 , by imposing observational constraints on an extended mass function in a proper way. we have also provided an inflation model that successfully generates pbhs as all dm fulfilling this requirement. | inflationary primordial black holes as all dark matter |
we study for the first time the stability against scalar perturbations, and we compute the spectrum of quasinormal modes of three-dimensional charged black holes in einstein-power-maxwell nonlinear electrodynamics assuming running couplings. adopting the sixth order wentzel-kramers-brillouin (wkb) approximation we investigate how the running of the couplings change the spectrum of the classical theory. our results show that all modes corresponding to nonvanishing angular momentum are unstable both in the classical theory and with the running of the couplings, while the fundamental mode can be stable or unstable depending on the running parameter and the electric charge. | quasinormal modes of scale dependent black holes in (1 +2 )-dimensional einstein-power-maxwell theory |
we consider the computation of volumes contained in a spatial slice of ads3 in terms of observables in a dual cft. our main tool is kinematic space, defined either from the bulk perspective as the space of oriented bulk geodesics, or from the cft perspective as the space of entangling intervals. we give an explicit formula for the volume of a general region in a spatial slice of ads3 as an integral over kinematic space. for the region lying below a geodesic, we show how to write this volume purely in terms of entangling entropies in the dual cft. this expression is perhaps most interesting in light of the complexity = volume proposal, which posits that complexity of holographic quantum states is computed by bulk volumes. an extension of this idea proposes that the holographic subregion complexity of an interval, defined as the volume under its ryu-takayanagi surface, is a measure of the complexity of the corresponding reduced density matrix. if this is true, our results give an explicit relationship between entanglement and subregion complexity in cft, at least in the vacuum. we further extend many of our results to conical defect and btz black hole geometries. | holographic subregion complexity from kinematic space |
we study the formation of primordial black holes when they are generated by the collapse of large overdensities in the early universe. since the density contrast is related to the comoving curvature perturbation by a nonlinear relation, the overdensity statistics is unavoidably non-gaussian. we show that the abundance of primordial black holes at formation may not be captured by a perturbative approach which retains the first few cumulants of the non-gaussian probability distribution. we provide two techniques to calculate the non-gaussian abundance of primordial black holes at formation, one based on peak theory and the other on threshold statistics. our results show that the unavoidable non-gaussian nature of the inhomogeneities in the energy density makes it harder to generate pbhs. we provide simple (semi-)analytical expressions to calculate the non-gaussian abundances of the primordial black holes and show that for both narrow and broad power spectra the gaussian case from threshold statistics is reproduced by increasing the amplitude of the power spectrum by a factor script o(2÷ 3). | the ineludible non-gaussianity of the primordial black hole abundance |
we analyze the motion of a massless and chargeless particle very near to the event horizon. it reveals that the radial motion has exponential growing nature which indicates that there is a possibility of inducing chaos in the particle motion of an integrable system when it comes under the influence of the horizon. this is being confirmed by investigating the poincaré section of the trajectories with the introduction of a harmonic trap to confine the particle's motion. two situations are investigated: (a) any static, spherically symmetric black hole and, (b) spacetime represents a stationary, axisymmetric black hole (e.g., kerr metric). in both cases, the largest lyapunov exponent has upper bound which is the surface gravity of the horizon. we find that the inclusion of rotation in the spacetime introduces more chaotic fluctuations in the system. the possible implications are finally discussed. | presence of horizon makes particle motion chaotic |
some ads3 × m7 type iib vacua have been recently proposed to arise from d3-branes wrapped on a spindle, a sphere with conical singularities at the poles. we explicitly construct a generalization of these solutions corresponding to a class of electrically charged and rotating supersymmetric black strings in ads5 × s5 with general magnetic fluxes on the spindle. we then perform a counting of their microstates using the charged cardy formula. to this purpose, we derive the general form of the anomaly polynomial of the dual n = (0, 2) cft in two dimensions and we show that it can be obtained via a simple gluing procedure. | rotating multi-charge spindles and their microstates |
we study the evolution of holographic subregion complexity under a thermal quench in this paper. from the subregion cv proposal in the ads/cft correspondence, the subregion complexity in the cft is holographically captured by the volume of the codimension-one surface enclosed by the codimension-two extremal entanglement surface and the boundary subregion. under a thermal quench, the dual gravitational configuration is described by a vaidya-ads spacetime. in this case we find that the holographic subregion complexity always increases at early time, and after reaching a maximum it decreases and gets to saturation. moreover we notice that when the size of the strip is large enough and the quench is fast enough, in adsd+1( d ≥ 3) spacetime the evolution of the complexity is discontinuous and there is a sudden drop due to the transition of the extremal entanglement surface. we discuss the effects of the quench speed, the strip size, the black hole mass and the spacetime dimension on the evolution of the subregion complexity in detail numerically. | holographic subregion complexity under a thermal quench |
large-amplitude density perturbations may have collapsed during the radiation dominated epoch of the universe to form primordial black holes (pbhs). there are several constraints to the abundance of pbhs that stem from evaporation or gravitational effects. due to the connection between primordial perturbations and the formation of pbhs, constraints on the present-day abundance of pbhs can be translated into limits on the primordial curvature power spectrum. we introduce several new observational and forecasted constraints to the amplitude of the primordial power spectrum and incorporate in our analysis uncertainties in the critical overdensity for collapse and considerations of ellipsoidal collapse. our results provide the most stringent limits from pbhs on the primordial curvature power spectrum on small scales. | constraints on the primordial curvature power spectrum from primordial black holes |
in this paper, we prove precise late-time asymptotics for solutions to the wave equation supported on angular frequencies greater or equal to $\ell$ on the domain of outer communications of subextremal reissner-nordström spacetimes up to and including the event horizon. our asymptotics yield, in particular, sharp upper and lower decay rates which are consistent with price's law on such backgrounds. we present a theory for inverting the time operator and derive an explicit representation of the leading-order asymptotic coefficient in terms of the newman-penrose charges at null infinity associated with the time integrals. our method is based on purely physical space techniques. for each angular frequency $\ell$ we establish a sharp hierarchy of $r$-weighted radially commuted estimates with length $2\ell+5$. we complement this hierarchy with a novel hierarchy of weighted elliptic estimates of length $\ell+1$. | price's law and precise late-time asymptotics for subextremal reissner-nordström black holes |
we consider rotating, electrically charged, supersymmetric ads black holes in four, five, six and seven dimensions, and provide a derivation of the respective extremization principles stating that the bekenstein-hawking entropy is the legendre transform of a homogeneous function of chemical potentials, subject to a complex constraint. extending a recently proposed bps limit, we start from finite temperature and reach extremality following a supersymmetric trajectory in the space of complexified solutions. we show that the entropy function is the supergravity on-shell action in this limit. chemical potentials satisfying the extremization equations also emerge from the complexified solution. | the bps limit of rotating ads black hole thermodynamics |
we argue that the proper time from the event horizon to the black hole singularity can be extracted from the thermal expectation values of certain operators outside the horizon. this works for fields which couple to higher-curvature terms, so that they can decay into two gravitons. to extract this proper time, it is necessary to vary the mass of the field. | proper time to the black hole singularity from thermal one-point functions |
we investigate how the next generation gravitational-wave (gw) detectors, such as einstein telescope (et) and cosmic explorer (ce), can be used to distinguish primordial black holes (pbhs) from astrophysical black holes (abhs). since a direct detection of sub-solar mass black holes can be taken as the smoking gun for pbhs, we estimate the detectable limits of the abundance of sub-solar mass pbhs in cold dark matter by the targeted search for sub-solar mass pbh binaries and binaries containing a sub-solar mass pbh and a super-solar mass pbh, respectively. on the other hand, according to the different redshift evolutions of the merger rate for pbh binaries and abh binaries, we forecast the detectable event rate distributions for the pbh binaries and abh binaries by et and ce respectively, which can serve as a method to distinguish super-solar mass pbhs from abhs. | distinguishing primordial black holes from astrophysical black holes by einstein telescope and cosmic explorer |
inflationary models predicting a scale-dependent large amplification of the density perturbations have recently attracted a lot of attention because the amplified perturbations can seed a sizable amount of primordial black holes (pbhs) and stochastic background of gravitational waves (gws). while the power spectra in these models are computed based on the linear equation of motion, it is not obvious whether loop corrections are negligible when such a large amplification occurs during inflation. in this paper, as a first step to discuss the loop corrections in such models, we use the in-in formalism and calculate the one-loop scalar power spectrum numerically and analytically in an illustrative model where the density perturbations are resonantly amplified due to oscillatory features in the inflaton potential. our calculation is technically new in that the amplified perturbations are numerically taken into account in the in-in formalism for the first time. in arriving at our analytical estimates, we highlight the role that the wronskian condition of perturbations, automatically satisfied in our model, plays in obtaining the correct estimates. in addition, the analytical estimates show that the contribution originating from the quantum nature of the perturbations in the loop can be dominant. we also discuss the necessary conditions for subdominant loop corrections in this model. we find that, for the typical parameter space leading to the 𝒪(107) amplification of the power spectrum required for a sufficient pbh production, the one-loop power spectrum dominates over the tree-level one, indicating the breakdown of the perturbation theory. | questions on calculation of primordial power spectrum with large spikes: the resonance model case |
in this letter, employing the generalized off-shell free energy, we treat black hole solutions as defects in the thermodynamic parameter space. the results show that the positive and negative winding numbers corresponding to the defects indicate the local thermodynamical stable and unstable black hole solutions, respectively. the topological number defined as the sum of the winding numbers for all the black hole branches at an arbitrary given temperature is found to be a universal number independent of the black hole parameters. moreover, this topological number only depends on the thermodynamic asymptotic behaviors of the black hole temperature at small and large black hole limits. different black hole systems are characterized by three classes via this topological number. this number could help us in better understanding the black hole thermodynamics and, further, shed new light on the fundamental nature of quantum gravity. | black hole solutions as topological thermodynamic defects |
by exploiting the kerr-schild gauge, we study the scattering of a massive (charged) scalar off a kerr-newman black hole. in this gauge, the interactions between the probe and the target involve only tri-linear vertices. we manage to write down the tree-level scattering amplitudes in analytic form, from which we can construct an expression for the eikonal phase which is exact in the spin of the black hole at arbitrary order in the post-minkowskian expansion. we compute the classical contribution to the cross-section and deflection angle at leading order for a kerr black hole for arbitrary orientation of the spin. finally, we test our method by reproducing the classical amplitude for a schwarzschild black hole at second post-minkowskian order and outline how to extend the analysis to the kerr-newman case. | a rutherford-like formula for scattering off kerr-newman bhs and subleading corrections |
in this work, we present a convenient method to perform the topological analysis of black hole thermodynamics. utilizing the spinodal curve, thermodynamic critical points of a black hole are endowed with a topological quantity, brouwer degree, which reflects intrinsic properties of the system under smooth deformations. particularly, in our setup it can be easily calculated without an exact solution of critical points. this enables us to conveniently investigate the topological transition between different thermodynamic systems, and give a topological classification for them. in this framework, topology of lovelock ads black holes with spherical horizon geometry is explored. results show that charged black holes in arbitrary dimensions can be classified into the same topology class, whereas the d =7 and d ≥8 uncharged black holes are in different topology classes. moreover, we revisit the relation between different phase structures of these black holes from the viewpoint of topology. some general topological properties of critical points are also discussed. | topology of black hole thermodynamics in lovelock gravity |
recently glavan and lin (2020) formulated a novel einstein-gauss-bonnet gravity in which the gauss-bonnet coupling has been rescaled as α /(d - 4) and the 4 d theory is defined as the limit d → 4 , which preserves the number degrees of freedom thereby free from the ostrogradsky instability. we present exact spherically symmetric nonstatic null dust solutions in the novel 4d einstein-gauss-bonnet gravity that bypasses the lovelock theorem. our solution represents radiating black holes and regains, in the limit α → 0 , the famous vaidya black hole of general relativity (gr). we discuss the horizon structure of black hole solutions to find that the three horizon-like loci that characterizes its structure, viz. ah , eh and tls have the relationship reh <rah =rtls. the charged radiating black holes in the theory, generalizing bonnor-vaidya black holes, are also considered. in particular our results, in the limit α → 0 , reduced exactly to vis-à-vis 4 d black holes of gr. | radiating black holes in the novel 4d einstein-gauss-bonnet gravity |
the focusing optics of nustar have enabled high signal-to-noise ratio spectra to be obtained from many x-ray bright active galactic nuclei (agn) and galactic black hole binaries (bhb). spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness-temperature (θ - ℓ) diagram which is forbidden due to runaway pair production. the coincidence suggests that pair production and annihilation are essential ingredients in the coronae of agn and bhb and that they control the shape of the observed spectra. | properties of agn coronae in the nustar era |
quantum complexity is conjectured to probe inside of black hole horizons (or wormholes) via gauge gravity correspondence. in order to have a better understanding of this correspondence, we study time evolutions of complexities for abelian pure gauge theories. for this purpose, we discretize the u (1 ) gauge group as zn and also the continuum spacetime as lattice spacetime, and this enables us to define a universal gate set for these gauge theories and to evaluate time evolutions of the complexities explicitly. we find that to achieve a large complexity ∼exp (entropy), which is one of the conjectured criteria necessary to have a dual black hole, the abelian gauge theory needs to be maximally nonlocal. | time evolution of complexity in abelian gauge theories |
we study the influence of the cosmic expansion on the size of the shadow of a spinning black hole observed by a comoving observer. we first consider that the expansion is driven by a cosmological constant only and build the connection between the kerr-de sitter metric and the friedmann--lemaître--robertson--walker metric. we clarify that the notion of a comoving observer is well defined in the spacetime of a spinning black hole only in the sense of being asymptotic. the angular size of the shadow for a comoving observer is calculated. significantly we find that the angular size approaches a nonzero finite value for a distant comoving observer, while it vanishes for a distant static observer. furthermore, by adopting the approximate method proposed in [g. s. bisnovatyi-kogan and o. y. tsupko, phys. rev. d 98, 084020 (2018)., 10.1103/physrevd.98.084020] we extend the study to the general multicomponent universe case. the results show that the difference between the horizontal and vertical angular size changes a lot, while their ratio, i.e., the oblateness, keeps unchanged when the supermassive spinning black hole is at a high redshift, due to the common amplification factor exerted by the cosmic expansion. in addition, when a =0 , our results agree with the previous studies in [v. perlick, o. y. tsupko, and g. s. bisnovatyi-kogan, phys. rev. d 97, 104062 (2018)., 10.1103/physrevd.97.104062, g. s. bisnovatyi-kogan and o. y. tsupko, phys. rev. d 98, 084020 (2018)., 10.1103/physrevd.98.084020]. | shadow of a spinning black hole in an expanding universe |
einstein-gauss-bonnet (egb) gravity is an outcome of quadratic curvature corrections to the einstein-hilbert gravity action in the form of a gauss-bonnet (gb) term in d > 4 dimensions and egb gravity is topologically invariant in 4 d . recently several ways have been proposed for regularizing, a d → 4 limit of egb, for nontrivial gravitational dynamics in 4 d . motivated by the importance of anti-de sitter gravity/conformal field theory correspondence (ads/cft), we analyse black holes with ads asymptotic of regularized 4 d egb gravity coupled to the nonlinear electrodynamics (ned) field. for a static spherically symmetric ansatz the field equations are solved exactly, using two different approaches, for a ned lagrangian to obtain an identical solution -namely ned charged ads black holes in 4 d egb gravity which retains several known solutions. owing to the ned charge corrected egb black holes, the thermodynamic quantities are also modified, and the entropy does not obey the usual area law. we calculate the heat capacity and helmholtz free energy, in terms of horizon radii, to investigate both local and global thermodynamic stability of black holes. we observe a secondary hawking-page transition between the smaller thermally favoured black hole and thermal ads space. our results show that the behaviour of hawking's evaporation abruptly halts at shorter radii regime such that the black holes do have a thermodynamically stable remnant with vanishing temperature. | phase transition of ads black holes in 4d egb gravity coupled to nonlinear electrodynamics |
we calculate the gravitational waves (gws) induced by the density fluctuations due to the inhomogeneous distribution of primordial black holes (pbhs) in the case where pbhs eventually dominate and reheat the universe by hawking evaporation. the initial pbh density fluctuations are isocurvature in nature. we find that most of the induced gws are generated right after evaporation, when the universe transits from the pbh dominated era to the radiation dominated era and the curvature perturbation starts to oscillate wildly. the strongest constraint on the amount of the produced gws comes from the big bang nucleosynthesis (bbn). we improve previous constraints on the pbh fraction and find that it cannot exceed 10-4. furthermore, this maximum fraction decreases as the mass increases and reaches 10-12 for mpbh∼ 5×108 g, which is the largest mass allowed by the bbn constraint on the reheating temperature. considering that pbh may cluster above a given clustering scale, we also derive a lower bound on the scale of clustering. interestingly, the gw spectrum for mpbh∼ 104 -108 g enters the observational window of ligo and decigo and could be tested in the future. although we focus on the pbh dominated early universe in this paper, our methodology is applicable to any model with early isocurvature perturbation. | gravitational wave constraints on the primordial black hole dominated early universe |
we analytically investigate the shadows cast by rotating black holes in the asymptotically safe gravity (asg) by deriving complete null geodesics and observables using the hamilton-jacobi equation and carter separable method. it turns out that the apparent shape and size of the shadow depend on the asg parameters (ζ , γ) in addition to other black hole parameters (m , a). the size of black hole shadows monotonically decrease and shadows get more distorted with increasing values of asg parameters, when compared with the kerr black hole shadows. in turn, we use shadow observables to estimate black hole spin and asg parameters. noteworthy, we find that the deflection angle of the light has been modified by asg parameters to generalize the kerr deflection angle, and the corrections in deflection angle are of o (μas). in the vanishing limits of asg parameters our results smoothly reduced to the kerr black holes. the inferred circularity deviation δc ≤ 0 . 10 for the m87* black hole shadow merely constrains the asg parameter ζ, however, shadow angular diameter θd = 42 ± 3 μ as, within the 1 σ region, places bounds ζ ≤ 0 . 1324 for γ = 0 . 10 . | shadow and deflection angle of rotating black hole in asymptotically safe gravity |
in symmetric teleparallel gravities, where the independent connection is characterized by nonmetricity while curvature and torsion are zero, it is possible to find a coordinate system whereby the connection vanishes globally and covariant derivatives reduce to partial derivatives - the coincident gauge. in this paper we derive general transformation rules into the coincident gauge for spacetime configurations where the both the metric and connection are static and spherically symmetric, and write out the respective form of the coincident gauge metrics. taking different options in fixing the freedom in the connection allowed by the symmetry and the field equations, the schwarzschild metric in the coincident gauge can take for instance the cartesian, kerr-schild, and diagonal (isotropic-like) forms, while the bbmb black hole metric in symmetric teleparallel scalar-tensor theory a certain diagonal form fits the coincident gauge requirements but the cartesian and kerr-schild forms do not. different connections imply different value for the boundary term which could in principle be physically relevant, but simple arguments about the coincident gauge do not seem to be sufficient to fix the connection uniquely. as a byproduct of the investigation we also point out that only a particular subset of static spherically symmetric connections has vanishing nonmetricity in the minkowski limit. | coincident gauge for static spherical field configurations in symmetric teleparallel gravity |
gravitational waves (gws) emitted by generic black-hole binaries show a rich structure that directly reflects the complex dynamics introduced by the precession of the orbital plane, which poses a real challenge to the development of generic waveform models. recent progress in modelling these signals relies on an approximate decoupling between the nonprecessing secular inspiral and a precession-induced rotation. however, the latter depends in general on all physical parameters of the binary which makes modelling efforts as well as understanding parameter-estimation prospects prohibitively complex. here we show that the dominant precession effects can be captured by a reduced set of spin parameters. specifically, we introduce a single effective precession spin parameter, χp, which is defined from the spin components that lie in the orbital plane at some (arbitrary) instant during the inspiral. we test the efficacy of this parameter by considering binary inspiral configurations specified by the physical parameters of a corresponding nonprecessing-binary configuration (total mass, mass ratio, and spin components (anti)parallel to the orbital angular momentum), plus the effective precession spin applied to the larger black hole. we show that for an overwhelming majority of random precessing configurations, the precession dynamics during the inspiral are well approximated by our equivalent configurations. our results suggest that in the comparable-mass regime waveform models with only three spin parameters faithfully represent generic waveforms, which has practical implications for the prospects of gw searches, parameter estimation and the numerical exploration of the precessing-binary parameter space. | towards models of gravitational waveforms from generic binaries: ii. modelling precession effects with a single effective precession parameter |
spontaneous scalarisation of electrically charged, asymptotically flat reissner-nordström black holes (bhs) has been recently demonstrated to occur in einstein-maxwell-scalar (ems) models. this phenomenon is allowed by a non-minimal coupling between the scalar and the maxwell fields, and does not require non-minimal couplings of the scalar field to curvature invariants. ems bh scalarisation presents a technical simplification over the bh scalarisation that has been conjectured to occur in extended scalar-tensor gauss-bonnet (estgb) models. it is then natural to ask: (1) how universal are the conclusions extracted from the ems model? and (2) how much do these conclusions depend on the choice of the non-minimal coupling function? here we address these questions by performing a comparative analysis of several different forms for the coupling function including: exponential, hyperbolic, power-law and a rational function (fraction) couplings. in all of them we obtain and study the domain of existence of fundamental, spherically symmetric, scalarised bhs and compute, in particular, their entropy. the latter shows that scalarised ems bhs are always entropically preferred over the rn bhs with the same total charge to mass ratio q. this contrasts with the case of estgb, where for the same power-law coupling the spherical, fundamental scalarised bhs are not entropically preferred over the schwarzschild solution. also, while the scalarised solutions in the ems model for the exponential, hyperbolic and power-law coupling are very similar, the rational function coupling leads to a transition in the domain of existence, by virtue of a pole in the coupling function, into a region of ‘exotic’ solutions that violate the weak energy condition. furthermore, fully non-linear dynamical evolutions of unstable rn bhs with different values of q are presented. these show: (1) for sufficiently small q, scalarised solutions with (approximately) the same q form dynamically; (2) for large q, spontaneous scalarisation visibly decreases q; thus evolutions are non-conservative; (3) despite the existence of non-spherical, static scalarised solutions, the evolution of unstable rn bhs under non-spherical perturbations leads to a spherical scalarised bh. | spontaneous scalarisation of charged black holes: coupling dependence and dynamical features |
primordial black hole (pbh) formation is a more generic phenomenon than was once thought. the dynamics of a scalar field in inflationary universe can produce pbhs under mild assumptions regarding the scalar potential. in the early universe, light scalar fields develop large expectation values during inflation and subsequently relax to the minimum of the effective potential at a later time. during the relaxation process, an initially homogeneous scalar condensate can fragment into lumps via an instability similar to the gravitational (jeans) instability, where the scalar self-interactions, rather than gravity, play the leading role. the fragmentation of the scalar field into lumps (e.g. q-balls or oscillons) creates matter composed of relatively few heavy "particles", whose distribution is subject to significant fluctuations unconstrained by comic microwave background (cmb) observations and unrelated to the large-scale structure. if this matter component comes to temporarily dominate the energy density before the scalar lumps decay, pbhs can be efficiently produced during the temporary matter-dominated era. we develop a general analytic framework for description of pbh formation in this class of models. we highlight the differences between the scalar fragmentation scenario and other commonly considered pbh formation models. given the existence of the higgs field and the preponderance of scalar fields within supersymmetric and other models of new physics, pbhs constitute an appealing and plausible candidate for dark matter. | analytic description of primordial black hole formation from scalar field fragmentation |
we report on a numerical investigation of black hole evolution in an einstein dilaton gauss-bonnet (edgb) gravity theory where the gauss-bonnet coupling and scalar (dilaton) field potential are symmetric under a global change in sign of the scalar field (a ' ${\mathbb{z}}_{2}$?--> ' symmetry). we find that for sufficiently small gauss-bonnet couplings schwarzschild black holes are stable to radial scalar field perturbations, and are unstable to such perturbations for sufficiently large couplings. for the latter case, we provide numerical evidence that there is a band of coupling parameters and black hole masses where the end states are stable scalarized black hole solutions, in general agreement with the results of macedo et al (2019 phys. rev. d 99 104041). for gauss-bonnet couplings larger than those in the stable band, we find that an 'elliptic region' forms outside of the black hole horizon, indicating the theory does not possess a well-posed initial value formulation in that regime. | dynamics of a {\\mathbb{z}}_{2}?-> symmetric edgb gravity in spherical symmetry |
the cobordism conjecture states that any quantum gravity configuration admits, at topological level, a boundary ending spacetime. we study the dynamical realization of cobordism, as spacetime dependent solutions of einstein gravity coupled to scalars containing such end-of-the-world `branes'. the latter appear in effective theory as a singularity at finite spacetime distance at which scalars go off to infinite field space distance. we provide a local description near the end-of-the-world branes, in which the solutions simplify dramatically and are characterized in terms of a critical exponent, which controls the asymptotic profiles of fields and the universal scaling relations among the spacetime distance to the singularity, the field space distance, and the spacetime curvature. the analysis does not rely on supersymmetry. we study many explicit examples of such local dynamical cobordisms in string theory, including 10d massive iia, the 10d non-supersymmetric usp(32) theory, bubbles of nothing, 4d 𝒩 = 1 cosmic string solutions, the klebanov-strassler throat, dp-brane solutions, brane configurations related to the d1/d5 systems, and small black holes. our framework encompasses diverse recent setups in which scalars diverge at the core of defects, by regarding them as suitable end-of-the-world branes. we explore the interplay of local dynamical cobordisms with the distance conjecture and other swampland constraints. | at the end of the world: local dynamical cobordism |
for a static and spherically symmetric black hole, a photon sphere is composed of circular null geodesics of fixed radius, and plays an important role in observing the black hole. recently, in an einstein-maxwell-scalar model with a non-minimal coupling between the scalar and electromagnetic fields, a class of hairy black holes has been found to possess two unstable and one stable circular null geodesics on the equatorial plane, corresponding to three photon spheres outside the event horizon. in this paper, we study quasinormal modes of the scalar field, which are associated with these circular null geodesics, in the hairy black hole spacetime. in the eikonal regime with l ≫ 1, the real part of the quasinormal modes is determined by the angular velocity of the corresponding circular geodesics. the imaginary part of the quasinormal modes associated with the unstable circular null geodesics encodes the information about the lyapunov exponent of the corresponding circular geodesics. interestingly, we find long-lived and sub-long-lived modes, which are associated with the stable and one of the unstable circular null geodesics, respectively. due to tunneling through potential barriers, the damping times of the long-lived and sub-long-lived modes can be exponentially and logarithmically large in terms of l, respectively. | quasinormal modes of black holes with multiple photon spheres |
we study quantum corrections in the gravitational path integral around nearly $1/16$-bps black holes in asymptotically $ads_5 \times s^5$ space, dual to heavy states in 4d $\mathcal{n}=4$ super yang-mills. the analysis provides a gravitational explanation of why $1/16$-bps black holes exhibit an exact degeneracy at large $n$ and why all such states have the same charges, confirming the belief that the superconformal index precisely counts the entropy of extremal black holes. we show the presence of a gap of order $n^{-2}$ between the $1/16$-bps black holes and the lightest near-bps black holes within the same charge sector. this is the first example of such a gap for black holes states within the context of $ads_5$ holography. we also derive the spectrum of near-bps states that lie above this gap. our computation relies on finding the correct version of the $\mathcal{n}=2$ super-schwarzian theory which captures the breaking of the $su(1, 1|1)$ symmetry when the black hole has finite temperature and non-zero chemical potential. finally, we comment on possible stringy and non-perturbative corrections that can affect the black hole spectrum. | bps and near-bps black holes in $ads_5$ and their spectrum in $\\mathcal{n}=4$ sym |
interpreting horizon-scale observations of astrophysical black holes demands a general understanding of null geodesics in the kerr spacetime. these may be divided into two classes: "direct" rays that primarily determine the observational appearance of a given source, and highly bent rays that produce a nested sequence of exponentially demagnified images of the main emission: the so-called "photon ring." we develop heuristics that characterize the direct rays and study the highly bent geodesics analytically. we define three critical parameters γ , δ , and τ that respectively control the demagnification, rotation, and time delay of successive images of the source, thereby providing an analytic theory of the photon ring. these observable parameters encode universal effects of general relativity, independent of the details of the emitting matter. | lensing by kerr black holes |
we present an investigation of spinning black holes in einstein-gauss-bonnet-dilaton (egbd) theory. the solutions are found within a nonperturbative approach, by directly solving the field equations. these stationary axially symmetric black holes are asymptotically flat. they possess a nontrivial scalar field outside their regular event horizon. we present an overview of the parameter space of the solutions together with a study of their basic properties. we point out that the egbd black holes can exhibit some physical differences when compared to the kerr solution. for example, their mass is always bounded from below, while their angular momentum can exceed the kerr bound. also, in contrast to the kerr case, the extremal solutions are singular, with the scalar field diverging on the horizon. | spinning black holes in einstein-gauss-bonnet-dilaton theory: nonperturbative solutions |
we perform an extensive analysis of the statistics of axion masses and interactions in compactifications of type iib string theory, and we show that black hole superradiance excludes some regions of calabi-yau moduli space. regardless of the cosmological model, a theory with an axion whose mass falls in a superradiant band can be probed by the measured properties of astrophysical black holes, unless the axion self-interaction is large enough to disrupt formation of a condensate. we study a large ensemble of compactifications on calabi-yau hypersurfaces, with 1 ≤ h1,1 ≤ 491 closed string axions, and determine whether the superradiance conditions on the masses and self-interactions are fulfilled. the axion mass spectrum is largely determined by the kähler parameters, for mild assumptions about the contributing instantons, and takes a nearly-universal form when h1,1 ≫ 1. when the kähler moduli are taken at the tip of the stretched kähler cone, the fraction of geometries excluded initially grows with h1,1, to a maximum of ≈ 0.5 at h1,1 ≈ 160, and then falls for larger h1,1. further inside the kähler cone, the superradiance constraints are far weaker, but for h1,1 ≫ 100 the decay constants are so small that these geometries may be in tension with astrophysical bounds, depending on the realization of the standard model. | superradiance in string theory |
scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. a bump-like feature behaves like a local speed-breaker and lowers the speed of the scalar field, thereby locally enhancing the scalar power spectrum. a bump-like feature emerges naturally if the base inflaton potential vb(phi) contains a local correction term such as vb(phi)[1+ɛ(phi)] at phi=phi0. the presence of such a localised correction term at phi0 leads to a large peak in the curvature power spectrum and to an enhanced probability of black hole formation. remarkably this does not significantly affect the scalar spectral index ns and tensor to scalar ratio r on cmb scales. consequently such models can produce higher mass primordial black holes (mpbh>= 1 msolar) in contrast to models with `near inflection-point potentials' in which generating higher mass black holes severely affects ns and r. with a suitable choice of the base potential—such as the string theory based (kklt) inflation or the α-attractor models—the amplification of primordial scalar power spectrum can be as large as 107 which leads to a significant contribution of primordial black holes (pbhs) to the dark matter density today, fpbh = ω0, pbh/ω0,dm ~ o(1). interestingly, our results remain valid if the bump is replaced by a dip. in this case the base inflaton potential vb(phi) contains a negative local correction term such as vb(phi)[1-ɛ(phi)] at phi=phi0 which leads to an enhanced probability of pbh formation. we conclude that primordial black holes in the mass range 10-17 msolar <= mpbh <= 100 msolar can easily form in single field inflation in the presence of small bump-like and dip-like features in the inflaton potential. | primordial black holes from a tiny bump/dip in the inflaton potential |
the event horizon telescope (eht) observed the compact radio source, sagittarius a* (sgr a*), in the galactic center on 2017 april 5-11 in the 1.3 mm wavelength band. at the same time, interferometric array data from the atacama large millimeter/submillimeter array and the submillimeter array were collected, providing sgr a* light curves simultaneous with the eht observations. these data sets, complementing the eht very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for sgr a* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. while most of the light curves correspond to a low variability state of sgr a*, the april 11 observations follow an x-ray flare and exhibit strongly enhanced variability. all of the light curves are consistent with a red-noise process, with a power spectral density (psd) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. our results indicate a steepening of the psd slope for timescales shorter than 0.3 hr. the spectral energy distribution is flat at 220 ghz, and there are no time lags between the 213 and 229 ghz frequency bands, suggesting low optical depth for the event horizon scale source. we characterize sgr a*'s variability, highlighting the different behavior observed just after the x-ray flare, and use gaussian process modeling to extract a decorrelation timescale and a psd slope. we also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines. | millimeter light curves of sagittarius a* observed during the 2017 event horizon telescope campaign |
using non-extensive statistical mechanics, the bekenstein-hawking area law is obtained from microstates of black holes in loop quantum gravity, for arbitrary real positive values of the barbero-immirzi parameter (γ). the arbitrariness of γ is encoded in the strength of the "bias" created in the horizon microstates through the coupling with the quantum geometric fields exterior to the horizon. an experimental determination of γ will fix this coupling, leaving out the macroscopic area of the black hole to be the only free quantity of the theory. | non-extensive statistical mechanics and black hole entropy from quantum geometry |
spinning supermassive black holes (bhs) in active galactic nuclei (agn) magnetically launch relativistic collimated outflows, or jets. without angular momentum supply, such jets are thought to perish within $3$ orders of magnitude in distance from the bh, well before reaching kpc-scales. we study the survival of such jets at the largest scale separation to date, via 3d general relativistic magnetohydrodynamic simulations of rapidly spinning bhs immersed into uniform zero-angular-momentum gas threaded by weak vertical magnetic field. we place the gas outside the bh sphere of influence, or the bondi radius, chosen much larger than the bh gravitational radius, $r_\text{b}=10^3r_\text{g}$. the bh develops dynamically-important large-scale magnetic fields, forms a magnetically-arrested disk (mad), and launches relativistic jets that propagate well outside $r_\text{b}$ and suppress bh accretion to $1.5\%$ of the bondi rate, $\dot{m}_\text{b}$. thus, low-angular-momentum accretion in the mad state can form large-scale jets in fanaroff-riley (fr) type i and ii galaxies. subsequently, the disk shrinks and exits the mad state: barely a disk (bad), it rapidly precesses, whips the jets around, globally destroys them, and lets $5-10\%$ of $\dot{m}_\text{b}$ reach the bh. thereafter, the disk starts rocking back and forth by angles $90-180^\circ$: the rocking accretion disk (rad) launches weak intermittent jets that spread their energy over a large area and suppress bh accretion to $\lesssim 2 \% ~ \dot{m}_\text{b}$. because bad and rad states tangle up the jets and destroy them well inside $r_\text{b}$, they are promising candidates for the more abundant, but less luminous, class of fr0 galaxies. | jets with a twist: emergence of fr0 jets in 3d grmhd simulation of zero angular momentum black hole accretion |
we show that perturbations of a scalar field in the background of the black hole obtained with the starobinsky-bel-robinson gravity is unstable unless the dimensionless coupling $\beta$ describing the compactification of m-theory is small enough. in the sector of stability quasinormal spectrum show peculiar behavior both in the frequency and time domains: the ringing consists of two stages where two different modes dominate. the wkb method does not reproduce part of the spectrum including the fundamental mode, which is responsible for the first stage of the ringing. as a result, the correspondence between the high frequency quasinormal modes and characteristics of the null geodesics reproduces only one branch of the eikonal spectrum. the frequencies are obtained with the help of three methods (frobenius, wkb and time-domain integration) with excellent agreement among them. | black holes in starobinsky-bel-robinson gravity and the breakdown of quasinormal modes/null geodesics correspondence |
in this paper, we analyze deflection angle of photon from magnetized black hole within non-linear electrodynamics with parameter β . in doing so, we find the corresponding optical spacetime metric and then we calculate the gaussian optical curvature. using the gauss-bonnet theorem, we obtain the deflection angle of photon from magnetized black hole in weak field limits and show the effect of non-linear electrodynamics on weak gravitational lensing. we also analyzed that our results reduces into maxwell's electrodynamics and reissner-nordström (rn) solution with the reduction of parameters. moreover, we also investigate the graphical behavior of deflection angle w.r.t correction parameter, black hole charge and impact parameter. | deflection angle of photon from magnetized black hole and effect of nonlinear electrodynamics |
merger events can trigger gas accretion onto supermassive black holes (smbhs) sitting at the centre of galaxies, and form close pairs of active galactic nuclei (agn). the fraction of agn in pairs gives key information to constrain the environmental properties and evolution of smbhs and their host galaxies. however, the identification of dual agn is difficult, and only very few have been found in the distant universe so far. we report the serendipitous discovery of a triple agn and four dual agn (one considered as a candidate), with projected separations in the range 3-28 kpc. their agn classification is mostly based on classical optical emission line flux ratios, as observed with the near-infrared spectrograph (nirspec) on the james webb space telescope (jwst), and is complemented with additional multi-wavelength diagnostics. the identification of these multiple agn out of the 17 agn systems in our ga-nifs survey (i.e. ~ 20-30%), suggests that they might be more common than expected from the most recent cosmological simulations, which predict a fraction of dual agn at least one order of magnitude smaller. this work highlights the exceptional capabilities of nirspec for detecting distant dual agn, and prompts new investigations to better constrain their fraction across the cosmic time, and to inform upcoming cosmological simulations. | a surprisingly high number of dual active galactic nuclei in the early universe |
recent work has shown how on-shell three-point amplitudes in gauge theory and gravity, representing the coupling to massive particles, correspond in the classical limit to the curvature spinors of linearised solutions. this connection, made explicit via the kmoc formalism in split metric signature, turns the double copy of scattering amplitudes into the double copy of classical solutions. here, we extend this framework to the universal massless sector of supergravity, which is the complete double copy of pure gauge theory. our extension relies on a riemann-cartan curvature incorporating the dilaton and the b-field. in this setting, we can determine the most general double copy arising from the product of distinct gauge theory solutions, say a dyon and √{kerr}. this gives a double-copy interpretation to gravity solutions of the type kerr-taub-nut-dilaton-axion. we also discuss the extension to heterotic gravity. finally, we describe how this formalism for the classical double copy relates to others in the literature, namely (i) why it is an on-shell momentum space analogue of the convolutional prescription, and (ii) why a straightforward prescription in position space is possible for certain vacuum solutions. | ns-ns spacetimes from amplitudes |
the dynamics of black hole horizons has recently been linked to that of carrollian fluids. this results in a dictionary between geometrical quantities and those of a fluid with unusual properties due its underlying carrollian symmetries. in this work we explore this relation in dynamical settings with the interest of shedding light on either side by relevant observations. in particular: we discuss how the null surface where the carrollian fluid evolves is affected by its behavior; that the fluid's equilibration properties are tied to teleological considerations; the connection of higher derivative contributions as both source of energy and dissipation for the fluid and the non-linear behavior of black holes. this latter point, connects with discussions of non-linear modes in the relaxation to equilibrium of perturbed black holes. | non-linear black hole dynamics and carrollian fluids |
gravitational wave astronomy has set in motion a scientific revolution. to further enhance the science reach of this emergent field of research, there is a pressing need to increase the depth and speed of the algorithms used to enable these ground-breaking discoveries. we introduce deep filtering—a new scalable machine learning method for end-to-end time-series signal processing. deep filtering is based on deep learning with two deep convolutional neural networks, which are designed for classification and regression, to detect gravitational wave signals in highly noisy time-series data streams and also estimate the parameters of their sources in real time. acknowledging that some of the most sensitive algorithms for the detection of gravitational waves are based on implementations of matched filtering, and that a matched filter is the optimal linear filter in gaussian noise, the application of deep filtering using whitened signals in gaussian noise is investigated in this foundational article. the results indicate that deep filtering outperforms conventional machine learning techniques, achieves similar performance compared to matched filtering, while being several orders of magnitude faster, allowing real-time signal processing with minimal resources. furthermore, we demonstrate that deep filtering can detect and characterize waveform signals emitted from new classes of eccentric or spin-precessing binary black holes, even when trained with data sets of only quasicircular binary black hole waveforms. the results presented in this article, and the recent use of deep neural networks for the identification of optical transients in telescope data, suggests that deep learning can facilitate real-time searches of gravitational wave sources and their electromagnetic and astroparticle counterparts. in the subsequent article, the framework introduced herein is directly applied to identify and characterize gravitational wave events in real ligo data. | deep neural networks to enable real-time multimessenger astrophysics |
while static love number vanish identically for kerr black holes, we show that the corresponding dynamical tidal coefficients are generically non-zero and exhibit logarithmic behavior. the computational method employs a related but simpler scheme consistent with cft descriptions, low-frequency regimes and post-newtonian results. these coefficients are illustrated with a numerical examples. | dynamical love numbers for kerr black holes |
we develop a framework to compute the tidal response of a kerr-like compact object in terms of its reflectivity, compactness, and spin, both in the static and the frequency-dependent case. here we focus on the low-frequency regime, which can be solved fully analytically. we highlight some remarkable novel features, in particular: i) even in the zero-frequency limit, the tidal love numbers (tlns) depend on the linear-in-frequency dependence of the object's reflectivity in a nontrivial way. ii) intriguingly, the static limit of the frequency-dependent tlns is discontinuous, therefore the static tlns differ from the static limit of the (phenomenologically more interesting) frequency-dependent tlns. this shows that earlier findings regarding the static tlns of ultracompact objects correspond to a measure-zero region in the parameter space, though the logarithmic behavior of the tlns in the black hole limit is retained. iii) in the non-rotating case, the tlns generically vanish in the zero-frequency limit (just like for a black hole), except when the reflectivity is ${\cal r}=1+{\cal o}(m\omega)$, in which case they vanish with a model-dependent scaling, which is generically logarithmic, in the black-hole limit. the tlns initially grow with frequency, for any nonzero reflectivity, and then display oscillations and resonances tied up with the quasi-normal modes of the object. iv) for rotating compact objects, the tlns decrease when the reflectivity decreases or the rotation parameter increases. our results lay the theoretical groundwork to develop model-independent tests of the nature of compact objects using tidal effects in gravitational-wave signals. | dynamical tidal love numbers of kerr-like compact objects |
we interpret appropriate families of euclidean wormhole solutions of ads$_3$ gravity in individual 2d cfts as replica wormholes described by branching around the time-symmetric apparent horizons of black holes sourced by the backreaction of heavy point particles. these wormholes help describe a rich formalism to coarse grain pure states in 2d cfts dual to the black hole geometries because the wormhole amplitudes match with the renyi entropies of cft states obtained by decohering the pure states in a specific way. this formalism can be generalised to coarse grain pure states in several copies of the dual cft dual to multi-boundary black holes using wormhole solutions with higher genus boundaries using which we illustrate that coarse graining away the interior of multi-boundary black holes sets the mutual information between any two copies of the dual cft to zero. furthermore, this formalism of coarse graining pure states can be extended to decohere transition matrices between pure states which helps interpret more general families of wormhole solutions including those with non replica-symmetric boundary conditions in individual cfts. the pseudo entropy of the decohered transition matrices has interesting holographic interpretation in terms of the area of minimal surfaces on appropriate black hole or wormhole geometries. the wormhole solutions which show up in the coarse graining formalism also compute the renyi entropies of hawking radiation after the page time in a setup which generalizes the west coast model to 3d gravity. using this setup, we discuss the evaporation of one-sided black holes sourced by massive point particles and multi-boundary black holes in 3d gravity. | euclidean wormholes for individual 2d cfts |
the images of supermassive black holes surrounded by optically thin, radiatively inefficient accretion flows, like those observed with the event horizon telescope, are characterized by a bright ring of emission surrounding the black hole shadow. in the kerr spacetime, this bright ring, when narrow, closely traces the boundary of the shadow and can, with appropriate calibration, serve as its proxy. the present paper expands the validity of this statement by considering two particular spacetime geometries: a solution to the field equations of a modified gravity theory and another that parametrically deviates from kerr but recovers the kerr spacetime when its deviation parameters vanish. a covariant, axisymmetric analytic model of the accretion flow based on conservation laws and spanning a broad range of plasma conditions is utilized to calculate synthetic non-kerr black hole images, which are then analyzed and characterized. we find that in all spacetimes: (i) it is the gravitationally lensed unstable photon orbit that plays the critical role in establishing the diameter of the rings observed in black hole images, not the event horizon or the innermost stable circular orbit, (ii) bright rings in these images scale in size with, and encompass, the boundaries of the black hole shadows, even when deviating significantly from kerr, and (iii) uncertainties in the physical properties of the accreting plasma introduce subdominant corrections to the relation between the diameter of the image and the diameter of the black hole shadow. these results provide important new theoretical justification for using black hole images to probe and test the spacetimes of supermassive black holes. | black hole images as tests of general relativity: effects of spacetime geometry |
we discuss the horizon properties, shadow cast, and the weak gravitational lensing of charged rotating regular black holes, which in addition to mass (m ) and rotation parameter (a ) have an electric charge (q ) and magnetic charge (g ). the considered regular black holes are the generalization of the kerr (q =g =0 ) and kerr-newman (g =0 ) black holes. interestingly, for a given parameter set, the apparent size of the shadow monotonically decreases and the shadow gets more distorted with increasing charge parameter q . we put constraints on the black hole parameters with the aid of recent m87* shadow observation. the conserved quantities associated with the rotating regular black holes are calculated and also a brief description of the weak gravitational lensing using the gauss-bonnet theorem is presented. interestingly, the deflection angle decreases with the charge of the black hole. our results vis-à-vis go over to the kerr and kerr-newman black holes in the appropriate limits. | shadow cast and deflection of light by charged rotating regular black holes |
in this paper, we consider linearly charged dilatonic black holes and study their thermodynamical behavior in the context of phase transitions and thermodynamic geometry. we show that, depending on the values of the parameters, these black holes can undergo two types of phase transition. we also find that there are three critical behaviors near the critical points for these black holes: nonphysical unstable to physical stable, large to small, and small to large black-hole phase transitions. next, we employ a thermodynamical metric to study the thermodynamical geometry of these black holes. we show that the characteristic behavior of the ricci scalar of this metric enables one to recognize the type of phase transition and critical behavior of the black holes near phase-transition points. finally, we will extend thermodynamical space by considering the dilaton parameter as an extensive parameter. with this consideration, we will show that the weinhold, ruppeiner, and quevedo metrics provide extra divergencies that are not related to any phase-transition point, whereas our new method provides an effective mechanism to study phase transitions. | phase transition and thermodynamic geometry of einstein-maxwell-dilaton black holes |
self-contained and comprehensive, this definitive new edition of gravity and strings is a unique resource for graduate students and researchers in theoretical physics. from basic differential geometry through to the construction and study of black-hole and black-brane solutions in quantum gravity - via all the intermediate stages - this book provides a complete overview of the intersection of gravity, supergravity, and superstrings. now fully revised, this second edition covers an extensive array of topics, including new material on non-linear electric-magnetic duality, the electric-tensor formalism, matter-coupled supergravity, supersymmetric solutions, the geometries of scalar manifolds appearing in 4- and 5-dimensional supergravities, and much more. covering reviews of important solutions and numerous solution-generating techniques, and accompanied by an exhaustive index and bibliography, this is an exceptional reference work. | gravity and strings |
in the next few years, advanced ligo (aligo) may see gravitational waves (gws) from thousands of black hole (bh) mergers. this marks the beginning of a new precision tool for physics. here we show how to search for new physics beyond the standard model using this tool, in particular the qcd axion in the mass range μa∼10-14 to 10-10 ev . axions (or any bosons) in this mass range cause rapidly rotating bhs to shed their spin into a large cloud of axions in atomic bohr orbits around the bh, through the effect of superradiance (sr). this results in a gap in the mass vs spin distribution of bhs when the bh size is comparable to the axion's compton wavelength. by measuring the spin and mass of the merging objects observed at ligo, we could verify the presence and shape of the gap in the bh distribution produced by the axion. the axion cloud can also be discovered through the gws it radiates via axion annihilations or level transitions. a blind monochromatic gw search may reveal up to 1 05 bhs radiating through axion annihilations, at distinct frequencies within ∼3 % of 2 μa . axion transitions probe heavier axions and may be observable in future gw observatories. the merger events are perfect candidates for a targeted gw search. if the final bh has high spin, a sr cloud may grow and emit monochromatic gws from axion annihilations. we may observe the sr evolution in real time. | black hole mergers and the qcd axion at advanced ligo |
the palatini formalism, which assumes the metric and the affine connection as independent variables, is developed for gravitational theories in flat geometries. we focus on two particularly interesting scenarios. first, we fix the connection to be metric compatible, as done in the usual teleparallel theories, but we follow a completely covariant approach by imposing the constraints with suitable lagrange multipliers. for a general quadratic theory we show how torsion naturally propagates and we reproduce the teleparallel equivalent of general relativity as a particular quadratic action that features an additional lorentz symmetry. we then study the much less explored theories formulated in a geometry with neither curvature nor torsion, so that all the geometrical information is encoded in the non-metricity. we discuss how this geometrical framework leads to a purely inertial connection that can thus be completely removed by a coordinate gauge choice, the coincident gauge. from the quadratic theory we recover a simpler formulation of general relativity in the form of the einstein action, which enjoys an enhanced symmetry that reduces to a second linearised diffeomorphism at linear order. more general theories in both geometries can be formulated consistently by taking into account the inertial connection and the associated additional degrees of freedom. as immediate applications, the new cosmological equations and their newtonian limit are considered, where the role of the lapse in the consistency of the equations is clarified, and the schwarzschild black hole entropy is computed by evaluating the corresponding euclidean action. we discuss how the boundary terms in the usual formulation of general relativity are related to different choices of coordinates in its coincident version and show that in isotropic coordinates the euclidean action is finite without the need to introduce boundary or normalisation terms. finally, we discuss the double-copy structure of the gravity amplitudes and the bootstrapping of gravity within the framework of coincident general relativity. | teleparallel palatini theories |
motivated by recent developments of btz black holes and interesting results of massive gravity, we investigate massive btz black holes in the presence of maxwell and born-infeld (bi) electrodynamics. we study geometrical properties such as type of singularity and asymptotical behavior as well as thermodynamic structure of the solutions through canonical ensemble. we show that despite the existence of massive term, obtained solutions are asymptotically (a)ds and have a curvature singularity at the origin. then, we regard varying cosmological constant and examine the van der waals like behavior of the solutions in extended phase space. in addition, we employ geometrical thermodynamic approaches and show that using weinhold, ruppeiner and quevedo metrics leads to existence of ensemble dependency while hpem metric yields consistent picture. for neutral solutions, it will be shown that generalization to massive gravity leads to the presence of non-zero temperature and heat capacity for vanishing horizon radius. such behavior is not observed for linearly charged solutions while generalization to nonlinearly one recovers this property. | massive charged btz black holes in asymptotically (a)ds spacetimes |
we study how the matter dispersed when a supermassive black hole tidally disrupts a star joins an accretion flow. combining a relativistic hydrodynamic simulation of the stellar disruption with a relativistic hydrodynamics simulation of the subsequent debris motion, we track the evolution of such a system until ≃ 80% of the stellar mass bound to the black hole has settled into an accretion flow. shocks near the stellar pericenter and also near the apocenter of the most tightly bound debris dissipate orbital energy, but only enough to make its characteristic radius comparable to the semimajor axis of the most bound material, not the tidal radius as previously envisioned. the outer shocks are caused by post-newtonian relativistic effects, both on the stellar orbit during its disruption and on the tidal forces. accumulation of mass into the accretion flow is both non-monotonic and slow, requiring several to 10 times the orbital period of the most tightly bound tidal streams, while the inflow time for most of the mass may be comparable to or longer than the mass accumulation time. deflection by shocks does, however, cause some mass to lose both angular momentum and energy, permitting it to move inward even before most of the mass is accumulated into the accretion flow. although the accretion rate still rises sharply and then decays roughly as a power law, its maximum is ≃ 0.1× the previous expectation, and the timescale of the peak is ≃ 5× longer than previously predicted. the geometric mean of the black hole mass and stellar mass inferred from a measured event timescale is therefore ≃ 0.2× the value given by classical theory. | general relativistic hydrodynamic simulation of accretion flow from a stellar tidal disruption |
bekenstein proved that in einstein's gravity minimally coupled to one (or many) real, abelian, proca field, stationary black holes (bhs) cannot have proca hair. dropping bekenstein's assumption that matter inherits spacetime symmetries, we show this model admits asymptotically flat, stationary, axi-symmetric, regular on and outside an event horizon bhs with proca hair, for an even number of real (or an arbitrary number of complex) proca fields. to establish it, we start by showing that a test, complex proca field can form bound states, with real frequency, around kerr bhs: stationary proca clouds. these states exist at the threshold of superradiance. it was conjectured in [1, 2], that the existence of such clouds at the linear level implies the existence of a new family of bh solutions at the nonlinear level. we confirm this expectation and explicitly construct examples of such kerr bhs with proca hair (kbhsph). for a single complex proca field, these bhs form a countable number of families with three continuous parameters (adm mass, adm angular momentum and noether charge). they branch off from the kerr solutions that can support stationary proca clouds and reduce to proca stars [3] when the horizon size vanishes. we present the domain of existence of one family of kbhsph, as well as its phase space in terms of adm quantities. some physical properties of the solutions are discussed; in particular, and in contrast with kerr bhs with scalar hair, some spacetime regions can be counter-rotating with respect to the horizon. we further establish a no-proca-hair theorem for static, spherically symmetric bhs but allowing the complex proca field to have a harmonic time dependence, which shows bhs with proca hair in this model require rotation and have no static limit. kbhsph are also disconnected from kerr-newman bhs with a real, massless vector field. | kerr black holes with proca hair |
in this paper, we study light rays in a kazakov-solodukhin black hole. to this end, we use the optical geometry of the kazakov-solodukhin black hole within the gauss-bonnet theorem. we first show the effect of the deformation parameter a on the gaussian optical curvature, and then, we use the modern method popularized by gibbons and werner to calculate the weak deflection angle of light. our calculations of deflection angle show how gravitational lensing is affected by the deformation parameter a. moreover, we demonstrate the effect of a plasma medium on weak gravitational lensing by the kazakov-solodukhin black hole. we discuss that the increasing the deformation parameter a will increase the weak deflection angle of the black hole. our analysis also uncloak how one may find a observational evidence for a deformation parameter on the deflection angle. in addition, we studied the rigorous bounds of the kazakov-solodukhin black hole for the grey body factor and also studied the graphical behaviour of the bounds by fixing l =0 and m =1 and observed that increasing the deformation parameter a will decrease the rigorous bound tb of the black hole. | weak deflection angle of kazakov-solodukhin black hole in plasma medium using gauss-bonnet theorem and its greybody bonding |
inspired by the hayden-preskill protocol for black hole evaporation, we consider the dynamics of a quantum many-body qudit system coupled to an external environment, where the time evolution is driven by the continuous limit of certain 2-local random unitary circuits. we study both cases where the unitaries are chosen with and without a conserved u(1) charge and focus on two aspects of the dynamics. first, we study analytically and numerically the growth of the entanglement entropy of the system, showing that two different time scales appear: one is intrinsic to the internal dynamics (the scrambling time), while the other depends on the system-environment coupling. in the presence of a u(1) conserved charge, we show that the entanglement follows a page-like behavior in time: it begins to decrease in the middle stage of the "evaporation", and decreases monotonically afterwards. second, we study the time needed to retrieve information initially injected in the system from measurements on the environment qudits. based on explicit numerical computations, we characterize such time both when the retriever has control over the initial configuration or not, showing that different scales appear in the two cases. | a random unitary circuit model for black hole evaporation |
we consider scattering in quantum gravity and derive long-range classical and quantum contributions to the scattering of light-like bosons and fermions (spin-0, spin- 1/2 , spin-1) from an external massive scalar field, such as the sun or a black hole. this is achieved by treating general relativity as an effective field theory and identifying the non-analytic pieces of the one-loop gravitational scattering amplitude. it is emphasized throughout the paper how modern amplitude techniques, involving spinor-helicity variables, unitarity, and squaring relations in gravity enable much simplified computations. we directly verify, as predicted by general relativity, that all classical effects in our computation are universal (in the context of matter type and statistics). using an eikonal procedure we confirm the post-newtonian general relativity correction for light-like bending around large stellar objects. we also comment on treating effects from quantum ℏ dependent terms using the same eikonal method. | light-like scattering in quantum gravity |
gravitational waves from neutron star binary inspirals contain information on strongly interacting matter in unexplored, extreme regimes. extracting this requires robust theoretical models of the signatures of matter in the gravitational-wave signals due to spin and tidal effects. in fact, spins can have a significant impact on the tidal excitation of the quasinormal modes of a neutron star, which is not included in current state-of-the-art waveform models. we develop a simple approximate description that accounts for the coriolis effect of spin on the tidal excitation of the neutron star's quadrupolar and octupolar fundamental quasinormal modes and incorporate it in the seobnrv4t waveform model. we show that the coriolis effect introduces only one new interaction term in an effective action in the corotating frame of the star, and fix the coefficient by considering the spin-induced shift in the resonance frequencies that has been computed numerically for the mode frequencies of rotating neutron stars in the literature. we investigate the impact of relativistic corrections due to the gravitational redshift and frame-dragging effects, and identify important directions where more detailed theoretical developments are needed in the future. comparisons of our model to numerical-relativity simulations of double neutron star and neutron star black-hole binaries show improved consistency in the agreement compared to current models used in data analysis. | spin effects on neutron star fundamental-mode dynamical tides: phenomenology and comparison to numerical simulations |
using conformal field theory and localization tecniques we study the propagation of scalar waves in gravity backgrounds described by schrödinger like equations with fuchsian singularities. exact formulae for the connection matrices relating the asymptotic behaviour of the wave functions near the singularities are obtained in terms of braiding and fusion rules of the cft. the results are applied to the study of quasi normal modes, absorption cross sections, amplification factors, echoes and tidal responses of black holes (bh) and exotic compact objects (eco) in four and five dimensions. in particular, we propose a definition of dynamical love numbers in gravity. | cft description of bh's and eco's: qnms, superradiance, echoes and tidal responses |
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