arXiv subjects

Antonia M. Frassino

Publications and source records attributed to Antonia M. Frassino.

At least 19 recordsLinked to original sources

arXiv2026

Extreme mass ratio head-on collisions of black holes in Einstein-scalar-Gauss-Bonnet theory

The evolution of the event horizon when two black holes merge can be determined by resorting to ray-tracing techniques on a single black hole spacetime, under the assumption that the binary's mass ratio is infinite and the underlying gravity theory respects the equivalence principle. We extend this analysis to the head-on collision of non-spinning hairy black holes in Einstein-scalar-Gauss-Bonnet gravity. In such theories the scalar field is coupled to a higher curvature operator, leading to possible modifications of the background geometry and consequently of photon propagation. We study three families of coupling functions: linear, quadratic, and a particular exponential form. The first choice enjoys a shift symmetry and forces the presence of scalar hair in the spectrum of black hole solutions. The latter two couplings break the shift symmetry and allow for spontaneously scalarized hairy black holes, which coexist with the Schwarzschild black hole. For all three classes of theories studied, we find a merger duration that is longer than the corresponding time in general relativity, when keeping the size of the small black hole fixed, and for viably small values of the coupling constant. However, the case of the exponential coupling yields a non-monotonic merger duration, which can become shorter than the general relativity value for a sufficiently large coupling constant. We observe that the merger duration and the area increment generically track the behavior of the small black hole's photon ring. Finally, we also compare our results with recent numerical simulations by other groups, despite the dissimilar mass ratios considered.

gr-qc↗

arXiv2025

Weak Cosmic Censorship with spinning particles in Kerr-(A)dS spacetimes

We investigate the weak cosmic censorship conjecture by analyzing the dynamics of spinning timelike particles dropped along the rotational axis of an extremal Kerr (anti)de Sitter black hole. This idea was first considered in a seminal paper by Wald and later by Needham but both analyses were restricted to asymptotically flat spacetimes. We generalize these studies, involving spinning particles, to rotating spacetimes with non vanishing cosmological constant. We examine whether the absorption of such particles can overspin the black hole beyond extremality, potentially leading to the formation of a naked singularity. In asymptotically de Sitter spacetime, we find that particles that are captured cannot overspin the black hole. Similar conclusions hold also with anti-de Sitter asymptotics, but the analysis is more subtle, requiring careful consideration of the point particle approximation.

gr-qc↗

arXiv2025

Quantum censors: backreaction builds horizons

Cosmic censorship posits spacetime singularities remain concealed behind event horizons, preserving the determinism of General Relativity. While quantum gravity is expected to resolve singularities, we argue that cosmic censorship remains necessary whenever spacetime has a reliable semi-classical description. Using holography to construct exact solutions to semi-classical gravity, we show backreaction of quantum matter generates horizons -- quantum censors -- to thwart potential violations of censorship. Along with a quantum Penrose inequality, this provides compelling evidence cosmic censorship is robust, even nonperturbatively, in semi-classical gravity.

hep-th↗

arXiv2024

Tidal Love numbers of static black holes in anti-de Sitter

Tidal Love numbers of anti-de Sitter black holes are understood as linear response coefficients governing how the holographically dual plasma polarizes when the geometry of the space, in which the plasma lives, is deformed. So far, this picture has been applied only to black branes with plane wave perturbations. We fill the gap in the literature by performing the computation of tidal Love numbers for the four-dimensional Schwarzschild solution in global anti-de Sitter, which is dual to a conformal plasma on $S^2$. We conclude about the effect of the bulk gravitational perturbations on the boundary metric and stress tensor, responsible for the geometric polarization. The computation of the tidal Love numbers is performed in both Regge-Wheeler gauge and the Kodama-Ishibashi gauge-invariant approach. We spell out how to convert the tidal Love numbers determined in these two formalisms and find perfect agreement. We also relate the Kodama- Ishibashi formalism with the Kovtun-Starinets approach, which is particularly well suited for the holographic analysis of black branes. This allows us to compare with the tidal Love number results for black branes in anti-de Sitter, also finding agreement in the relevant regime.

hep-th↗

arXiv2024

The impact of higher derivative corrections to General Relativity on black hole mergers

The merging of two black holes is a notoriously difficult process to describe exactly. Nevertheless, the hindrances posed by gravity's nonlinearity can be circumvented by focusing on the strict extreme mass ratio limit, in which one of the black holes is infinitely larger than the other. Such an approach has been developed by Emparan and Martínez and applied within General Relativity to investigate the time evolution of event horizons melding, using nothing but elementary concepts in gravitational physics and simple integrations of geodesics. We apply this strategy to study black hole mergers in higher derivative gravity, in order to assess how the defining characteristics of the fusion process change as the gravitational theory is modified. We adopt the case of Einsteinian cubic gravity for concreteness, and determine how the mergers' duration and the relative area increment change as the theory's single coupling parameter is varied.

gr-qc↗

arXiv2024

Quantum inequalities for quantum black holes

We formulate spacetime inequalities applicable to quantum-corrected black holes to all orders of backreaction in semiclassical gravity. Namely, we propose refined versions of the quantum Penrose and reverse isoperimetric inequalities, valid for all known three-dimensional asymptotically anti-de Sitter quantum black holes. Previous proposals of the quantum Penrose inequality apply in higher dimensions but fail when applied in three dimensions beyond the perturbative regime. Our quantum Penrose inequality, valid in three dimensions, holds at all orders of backreaction. This suggests cosmic censorship must exist in non-perturbative semiclassical gravity. Our quantum reverse isoperimetric inequality implies a maximum entropy state for quantum black holes at fixed volume.

hep-th↗

arXiv2024

Reentrant phase transitions of quantum black holes

We show backreaction of quantum fields on black hole geometries can trigger new thermal phase transitions. Specifically, we study the phase behavior of the three-dimensional quantum-corrected static BTZ black hole, an exact solution to specific semi-classical gravitational equations due to quantum conformal matter, discovered through braneworld holography. Focusing on the canonical ensemble, for large backreaction, we find novel reentrant phase transitions as the temperature monotonically increases, namely, from thermal anti-de Sitter space to the black hole and back to thermal anti-de Sitter. The former phase transition is first-order, a quantum analog of the classical Hawking-Page phase transition, while the latter is zeroth-order and has no classical counterpart.

hep-th↗

arXiv2024

Weak cosmic censorship and the rotating quantum BTZ black hole

Tests of the weak cosmic censorship conjecture examine the possibility of the breakdown of predictivity of the gravitational theory considered, by checking if curvature singularities typically present in black hole spacetimes are concealed within an event horizon at all times. A possible method to perform such tests was proposed by Wald and consists in trying to overspin an extremal rotating black hole by throwing at it a test particle with large angular momentum. In this paper, we analyze the effects of dropping a test particle into an extremal quantum rotating BTZ black hole, whose three-dimensional metric captures the exact backreaction from strongly coupled quantum conformal fields. Our analysis reveals that, despite the inclusion of quantum effects, and akin to the classical scenario, these attempts to destroy the black hole are doomed to be unsuccessful. Particles carrying the maximum angular momentum and still falling into an extremal quantum BTZ black hole can, at most, leave it extremal. Nevertheless, we found numerical evidence that large backreaction of the quantum fields tends to disfavor violations of cosmic censorship.

hep-th↗

arXiv2023

Entropy Bounds for Rotating AdS Black Holes

We propose novel thermodynamic inequalities that apply to stationary asymptotically Anti-de Sitter (AdS) black holes. These inequalities incorporate the thermodynamic volume and refine the reverse isoperimetric inequality. To assess the validity of our conjectures, we apply them to a wide range of analytical black hole solutions, observing compelling evidence in their favour. Intriguingly, our findings indicate that these inequalities may also apply for black holes of non-spherical horizon topology, as we show their validity as well for thin black rings in AdS.

gr-qc↗

arXiv2023

Black hole-wormhole collisions and the emergence of islands

We use ray-tracing techniques to determine the evolution of the event horizon of a large black hole that ``gobbles'' a tiny, traversable wormhole. This calculation has physical meaning in the extreme mass ratio limit. Two setups are considered: a single-mouth wormhole connecting two otherwise independent universes, and a double-mouth zero-length wormhole within the same universe. In the first setting it turns out that, at early times, there exist two disconnected horizons, one in each universe, which then merge as the wormhole falls into the large black hole. In the second setup, we observe the appearance of an `island', a region of spacetime that is spatially disconnected from the exterior of the black hole, but in causal contact with future null infinity. The island shrinks as time evolves and eventually disappears after sufficient time has elapsed, as compared to the distance between the two mouths. This provides a communication channel with the interior of the large black hole for a certain time interval. We compute numerically the lifetime of the island and verify that it depends linearly on the inter-mouth distance. Extending the analysis to wormholes with finite length, we show that the achronal averaged null energy condition prevents the appearance of islands.

gr-qc↗

arXiv2023

Higher-dimensional origin of extended black hole thermodynamics

Holographic braneworlds are used to present a higher-dimensional origin of extended black hole thermodynamics. In this framework, classical, asymptotically anti-de Sitter black holes map to quantum black holes in one dimension less, with a conformal matter sector that backreacts on the brane geometry. Varying the brane tension alone leads to a dynamical cosmological constant on the brane, and, correspondingly, a variable pressure attributed to the brane black hole. Thus, standard thermodynamics in the bulk, including a work term coming from the brane, induces extended thermodynamics on the brane, exactly, to all orders in the backreaction. A microsopic interpretation of the extended thermodynamics of specific quantum black holes is given via double holography.

hep-th↗

arXiv2017

Unruh thermal hadronization and the cosmological constant

We use black holes with a negative cosmological constant to investigate aspects of the freeze-out temperature for hadron production in high energy heavy-ion collisions. The two black hole solutions present in the anti-de Sitter geometry have different mass and are compared to the data showing that the small black hole solution is in good agreement. This is a new feature in the literature since the small black hole in general relativity has different thermodynamic behavior from that of the large black hole solution. We find that the inclusion of the cosmological constant (which can be interpreted as the plasma pressure) leads to a lowering of the temperature of the freeze-out curve as a function of the baryochemical potential, improving the description previously suggested by Castorina, Kharzeev, and Satz.

hep-th↗

arXiv2017

Thermodynamics of Quantum Phase Transitions of a Dirac oscillator in a homogenous magnetic field

The Dirac oscillator in a homogenous magnetic field exhibits a chirality phase transition at a particular (critical) value of the magnetic field. Recently, this system has also been shown to be exactly solvable in the context of noncommutative quantum mechanics featuring the interesting phenomenon of re-entrant phase transitions. In this work we provide a detailed study of the thermodynamics of such quantum phase transitions (both in the standard and in the noncommutative case) within the Maxwell-Boltzmann statistics pointing out that the magnetization has discontinuities at critical values of the magnetic field even at finite temperatures.

cond-mat.stat-mech↗

arXiv2017

Unparticle Casimir effect

In this paper we present the un-Casimir effect, namely the study of the Casimir energy in the presence of an unparticle component in addition to the electromagnetic field contribution. The distinctive feature of the un-Casimir effect is a fractalization of metallic plates. This result emerges through a new dependence of the Casimir energy on the plate separation that scales with a continuous power controlled by the unparticle dimension. As long as the perfect conductor approximation is valid, we find bounds on the unparticle scale that are independent of the effective coupling constant between the scale invariant sector and ordinary matter. We find regions of the parameter space such that for plate distances around $5μ$m and larger the un-Casimir bound wins over the other bounds.

hep-ph↗

arXiv2016

Critical points in Lovelock Black Holes

We review some of the results obtained by introducing a thermodynamic pressure via the cosmological constant in a class of higher curvature theories known as Lovelock gravity. In particular, we focus on a specific relation between the higher-order Lovelock couplings that introduces a peculiar isolated critical point for hyperbolic black holes characterized by non-standard critical exponents.

hep-th↗

arXiv2016

Geometric model of black hole quantum $N$-portrait, extradimensions and thermodynamics

Recently a short scale modified black hole metric, known as holographic metric, has been proposed in order to capture the self-complete character of gravity. In this paper we show that such a metric can reproduce some geometric features expected from the quantum $N$-portrait beyond the semi-classical limit. We show that for a generic $N$ this corresponds to having an effective energy momentum tensor in Einstein equations or, equivalently, non-local terms in the gravity action. We also consider the higher dimensional extension of the metric and the case of an AdS cosmological term. We provide a detailed thermodynamic analysis of both cases, with particular reference to the repercussions on the Hawking-Page phase transition.

gr-qc↗

arXiv2016

On the universality of thermodynamics and $η/s$ ratio for the charged Lovelock black branes

We investigate general features of charged Lovelock black branes by giving a detailed description of geometrical, thermodynamic and holographic properties of charged Gauss-Bonnet (GB) black branes in five dimensions. We show that when expressed in terms of effective physical parameters, the thermodynamic behaviour of charged GB black branes is completely indistinguishable from that of charged Einstein black branes. Moreover, the extremal, near-horizon limit of the two classes of branes is exactly the same as they allow for the same AdS$_2\times R_3$, near-horizon, exact solution. This implies that, although in the UV the associated dual QFTs are different, they flow in the IR to the same fixed point. The calculation of the shear viscosity to entropy ratio $η/s$ confirms these results. Despite the GB dual plasma has in general a non-universal temperature-dependent $η/s$, it flows monotonically to the universal value $1/4π$ in the IR. For negative (positive) GB coupling constant, $η/s$ is an increasing (decreasing) function of the temperature and the flow respects (violates) the KSS bound.

hep-th↗

arXiv2016

Lower-Dimensional Black Hole Chemistry

The connection between black hole thermodynamics and chemistry is extended to the lower-dimensional regime by considering the rotating and charged BTZ metric in the $(2+1)$-D and a $(1+1)$-D limits of Einstein gravity. The Smarr relation is naturally upheld in both BTZ cases, where those with $Q \ne 0$ violate the Reverse Isoperimetric Inequality and are thus superentropic. The inequality can be maintained, however, with the addition of a new thermodynamic work term associated with the mass renormalization scale. The $D\rightarrow 0$ limit of a generic $D+2$-dimensional Einstein gravity theory is also considered to derive the Smarr and Komar relations, although the opposite sign definitions of the cosmological constant and thermodynamic pressure from the $D>2$ cases must be adopted in order to satisfy the relation. The requirement of positive entropy implies a lower bound on the mass of a $(1+1)$-D black hole. Promoting an associated constant of integration to a thermodynamic variable allows one to define a "rotation" in one spatial dimension. Neither the $D=3$ nor the $D \rightarrow 2$ black holes exhibit any interesting phase behaviour.

gr-qc↗