Article
Astronomy & Astrophysics
Kunal Pal, Kuntal Pal, Rajibul Shaikh, Tapobrata Sarkar
Summary: By observing the shadows of M87* and Sgr A*, we studied a rotating version of a modified Janis-Newman-Winicour metric and constrained the size of the wormhole using parameter values. The results show that the case of a naked singularity is inconsistent with the observations, while the shadow formed by the wormhole branch is consistent with the observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Particles & Fields
Divyesh N. Solanki, Parth Bambhaniya, Dipanjan Dey, Pankaj S. Joshi, Kamlesh N. Pathak
Summary: In this paper, a rotating Janis-Newman-Winicour (JNW) naked singularity spacetime is constructed using the Newman-Janis Algorithm (NJA). The shadows cast by the rotating JNW naked singularity are studied and compared with the shadows cast by the Kerr black hole. It is found that the shadow of the rotating naked singularity can be distinguished from the shadow of the Kerr black hole. Additionally, the precession of timelike bound orbits in rotating JNW spacetime is analyzed and a negative precession is observed, which is not present in the Kerr black hole case. These novel signatures of the shadow and orbital precession in rotating JNW naked singularity spacetime could be important in the context of recent astronomical observations.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Aydin Tavlayan, Bayram Tekin
Summary: The existence of light rings is closely related to black hole horizons and observables. We extend the arguments for unstable light rings in four-dimensional black holes to five-dimensional black holes, and show that there is a light ring for each rotation sense in a stationary black hole. Additionally, we find that when the black hole horizon disappears and the singularity becomes naked, only one of the light rings survives.
Article
Astronomy & Astrophysics
Kimet Jusufi
Summary: In this letter, a new class of black hole solutions with different topology, namely, a torus-like black hole and a black string in the presence of the cosmological constant, are extended based on the recent black hole solution with spherical symmetry. Regularized expressions for the gravitational and electromagnetic potentials are used, and the corrections to the energy density are derived. The obtained black hole solutions are regular in the limit r-+0, and it is found that the total mass of the black hole is corrected due to the regularized self-energy of the electrostatic field. Well-known solutions in the literature are recovered in the special limit.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Naoki Tsukamoto
Summary: This paper investigates retrolensing by two photon spheres in a novel black-bounce spacetime proposed by Lobo et al., which can correspond to different types of black holes and wormholes. In the case of a wormhole, there are two photon spheres inside and outside the wormhole, and the light rays reflected by these photon spheres can have an impact on the retrolensing light curves.
Article
Physics, Particles & Fields
Raul Carballo-Rubio, Francesco Di Filippo, Stefano Liberati, Costantino Pacilio, Matt Visser
Summary: This paper investigates the effect of inner horizon surface gravity on the stability of black holes and finds that regular black holes typically exhibit exponential instability. However, by constructing specific geometries, it is possible to avoid this instability and provide an interesting alternative solution.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Astronomy & Astrophysics
R. A. Konoplya, A. Zhidenko
Summary: This article proposes a simple metric which parameterizes spherically symmetric and asymptotically flat black holes, taking into account the post-Newtonian constraints and basic astrophysical characteristics. By varying the values of three parameters, two distinctive features can be obtained: the temperature and Hawking radiation of the black hole, as well as the outburst of overtones that are highly sensitive to small changes in the parameters.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Particles & Fields
Raul Carballo-Rubio, Francesco Di Filippo, Stefano Liberati, Matt Visser
Summary: This paper presents a systematic study of the geometric structure of non-singular spacetimes describing black holes in Lorentz-violating gravity. The concept of trapping horizons and marginally trapped surfaces is reviewed and their significance in frameworks with modified dispersion relations is studied. The notion of universally marginally trapped surfaces is introduced as a generalization for frameworks with infinite signal velocities, leading to the definition of universal trapping horizons. The interplay between the kinematical part of Penrose's singularity theorem and the existence of multiple different metrics is explored, resulting in a complete classification of all possible geometries without incomplete physical trajectories or curvature singularities. The taxonomy of geodesically complete black holes in Horava-like frameworks includes scenarios such as evaporating regular black holes, regular black holes bouncing into regular white holes, and hidden wormholes.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Archil Kobakhidze, Zachary S. C. Picker
Summary: By analysing the nature of the horizon, we demonstrate the validity of the Thakurta metric in describing cosmological black holes, contrary to some claims in the literature.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
Moslem Shafiee, Yousef Bahrampour
Summary: We study how quantum fields affect the collapse of a thin shell of dust through vacuum polarization and conformal anomaly. The fate of the collapse depends on the physical properties of the shell, and quantum effects can result in the modification of black hole geometry and structure. While most collapses result in a singularity, under certain conditions, a non-singular black hole can be formed, where the collapse stops at a radius larger than the Planck length.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Physics, Particles & Fields
Xiaobo Guo, Yuhang Lu, Benrong Mu, Peng Wang
Summary: We propose a conjecture about the relationship between Lyapunov exponents and black hole phase transitions. By calculating the Lyapunov exponents of particles and ring strings in Reissner-Nordstrom-AdS black holes, we find that the Lyapunov exponents become multivalued during phase transitions and coincide with black hole phases. Furthermore, the discontinuous change in the Lyapunov exponents can be treated as an order parameter and has a critical exponent of 1/2 near the critical point.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Chiranjeeb Singha, Sumanta Chakraborty, Naresh Dadhich
Summary: The strong cosmic censorship conjecture has been validated for charged BTZ black holes and in certain gravitational theories. The study demonstrates that the key parameter associated with violation of the conjecture is always below the critical value in these cases, in contrast to higher dimensional black holes.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Astronomy & Astrophysics
Roberto Casadio
Summary: Classical general relativity predicts the occurrence of spacetime singularities under very general conditions. However, from the perspective of the complete quantum theory of matter and gravity, it is argued that this scenario cannot be physically realized since no proper quantum state may contain the infinite momentum modes required to resolve the singularity.
Article
Physics, Particles & Fields
Raul Carballo-Rubio, Francesco Di Filippo, Stefano Liberati, Costantino Pacilio, Matt Visser
Summary: The study explores regular black holes with nonsingular cores and their stability, introducing a generalization of the geometric framework to show that regular black holes have an exponentially growing Misner-Sharp mass at the inner horizon. This suggests that stable nonsingular black hole spacetimes may not be the final outcome of a quantum gravity regularization mechanism.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Physics, Particles & Fields
Athanasios Bakopoulos, Theodoros Nakas
Summary: This paper investigates a simple gravitational theory with a scalar field and studies analytic black-hole solutions with non-trivial scalar hair. The research finds stable ultra-compact black hole solutions under certain conditions.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Roberto Emparan, Marija Tomasevic
JOURNAL OF HIGH ENERGY PHYSICS
(2020)
Article
Physics, Particles & Fields
Roberto Emparan, Brianna Grado-White, Donald Marolf, Marija Tomasevic
Summary: This article discusses the construction of traversable wormholes with multiple mouths in four spacetime dimensions and the associated quantum entanglement. The solutions allow for traversal between any pair of mouths, with specific fundamental groups in the case of multiple mouths. By inserting black holes and extending possible magnetic fluxes or cosmic strings to infinity, the construction of these wormholes is achieved. Multiparty entanglement may also play a significant role in the traversability of these wormholes when AdS asymptotics are added to the construction.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Physics, Particles & Fields
Roberto Emparan, David Licht, Ryotaku Suzuki, Marija Tomasevic, Benson Way
Summary: We study the evolution of the Gregory-Laflamme instability for black strings in global AdS spacetime, and investigate the CFT dual of the formation of a bulk naked singularity. Using an effective theory in the large D limit, we uncover a rich variety of dynamical behaviour, depending on the thickness of the string and on initial perturbations. These include large inflows of horizon generators from the asymptotic boundary (a 'black tsunami'), a pinch-off of the horizon that likely reveals a naked singularity, and competition between these two behaviours, such as a nakedly singular pinch-off that subsequently gets covered by a black tsunami.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Roberto Emparan, Antonia Micol Frassino, Martin Sasieta, Marija Tomasevic
Summary: This study analyzes different holographic complexity proposals for black holes, considering corrections from bulk quantum fields. By focusing on the quantum BTZ black hole, the analysis accounts for the effects of conformal fields with large central charge and backreaction corrections to the BTZ metric. The results indicate that Volume Complexity exhibits a consistent quantum expansion and accurately reproduces known limits, while the Generalized Action Complexity fails to reproduce the expected classical limit due to large contributions from the singularity modified by quantum backreaction. Moreover, the doubly-holographic setup enables the computation of complexity purely from quantum fields, a concept that has been challenging in conventional holographic setups. In holographic induced-gravity scenarios, the complexity of quantum fields in a black hole background vanishes to leading order in the gravitational strength of CFT effects.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Roberto Emparan, Marija Tomasevic
Summary: This study explores the features of strongly interacting quantum fields in spacetimes with chronology horizons. It generalizes the holographic mechanism for chronology protection and computes the gravitational backreaction of the quantum fields, resulting in the transformation of the chronology horizon into a spacelike curvature singularity.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
David Licht, Raimon Luna, Ryotaku Suzuki
Summary: We investigate the phase space of non-uniform black branes on oblique lattices with numerous dimensions. We discover the phase diagrams for various periodicities and angles, and identify the thermodynamically favored phases for each lattice configuration. In a specific range of angles, we observe the metastability of certain phases.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Roberto Emparan, Marija Tomasevic
Summary: In this study, we use holography to investigate the reaction of interacting quantum fields to the presence of closed timelike curves in a dynamically changing background. We find that strongly coupled conformal theories in the corresponding two-dimensional spacetimes can be holographically described by three-dimensional AdS bulk geometries. We also discover that entangling the conformal field theories (CFTs) in two separate time machines connects them through a traversable bulk wormhole.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Marco Astorino, Roberto Emparan, Adriano Vigano
Summary: This paper argues that expanding bubbles of nothing are a common feature in systems of black holes with multiple or non-spherical horizons. The authors provide explicit constructions in four and five dimensions to demonstrate this idea, showing that the geometries of expanding bubbles arise as a limit of static black hole binaries and black rings. They also discuss the possibility of similar constructions in higher dimensions, although numerical methods are often required. The paper concludes by suggesting that the Nariai solution can be understood as containing an expanding circular bubble of nothing.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Roberto Emparan, Juan F. Pedraza, Andrew Svesko, Marija Tomasevic, Manus R. Visser
Summary: This study investigates the generation and thermodynamic properties of quantum black holes in three-dimensional de Sitter space, using both braneworld holography and non-holographic perturbative analysis. The results reveal similarities to classical four-dimensional black holes and provide insights into the holographic dual description of de Sitter spacetimes.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
Raimon Luna, Mikel Sanchez-Garitaonandia
Summary: In this study, collisions of Gaussian mass-density blobs in a holographic plasma are investigated using a large D effective theory as a model for holographic shockwave collisions. The first 4+1 collisions in Einstein-Maxwell theory, which correspond to collisions of matter with non-zero baryonic number, are successfully simulated using the simplicity of the effective theory. Several collision scenarios with different blob shapes, impact parameters, and charge values are explored, revealing that collisions with impact parameter below the transverse width of the blobs are equivalent under rescaling. The weak effect of charge on other quantities is also observed. The generation of entropy during collisions is studied, considering both charge diffusion and viscous dissipation, and multiple stages of linear entropy growth are identified, with rates dependent on the initial conditions.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Physics, Particles & Fields
Roberto Emparan, Raimon Luna, Ryotaku Suzuki, Marija Tomasevic, Benson Way
Summary: We describe the dynamical evaporation of a black hole as its classical evolution in an Anti-de Sitter braneworld. The intersection of the horizon of a bulk black hole with the brane gives the classical bulk dual of a black hole coupled to quantum conformal fields. The evaporation occurs when the bulk horizon slides off the brane and the horizon on the brane shrinks.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Astronomy & Astrophysics
Raimon Luna, Juan Calderon Bustillo, Juan Jose Seoane Martinez, Alejandro Torres-Forne, Jose A. Font
Summary: We use physics-informed neural networks (PINNs) to compute the first quasinormal modes of the Kerr geometry via the Teukolsky equation, providing accurate oscillation frequencies and damping times for black holes. The PINN-computed quasinormal modes are indistinguishable from existing methods at high signal-to-noise ratios (SNRs), making them reliable for gravitational-wave data analysis in the mid term. This technique may continue to be useful until the arrival of third-generation detectors with higher SNRs.
Article
Astronomy & Astrophysics
Raimon Luna, Gabriele Bozzola, Vitor Cardoso, Vasileios Paschalidis, Miguel Zilhao
Summary: In this study, we investigate the contributions of gravitational and electromagnetic radiation to the emission of linear momentum in quasicircular charged black hole binaries using fully general-relativistic numerical evolutions. We find that gravitational waves can emit momentum in the presence of electromagnetic fields, contrary to the vacuum case. Additionally, unequal mass binaries exhibit significant deviations of electromagnetic kicks from Keplerian predictions due to strong gravitational kicks. Moreover, the magnitudes of electromagnetic kicks are always smaller than gravitational ones for the charge-to-mass ratios considered in this work.
Article
Astronomy & Astrophysics
Pablo Bueno, Roberto Emparan, Quim Llorens
Summary: This study focuses on the structure of higher-curvature gravitational densities induced from holographic renormalization in AdS(d+1) and their definition of a higher-curvature gravitational theory on the brane in a braneworld construction. It is found that these densities satisfy a holographic c-theorem in general dimensions and the terms affecting the monotonicity of the holographic c-function are algebraic in curvature and do not involve covariant derivatives of the Riemann tensor.
Article
Astronomy & Astrophysics
Raimon Luna, Miguel Zilhao, Vitor Cardoso, Joao L. Costa, Jose Natario
Summary: The analysis of extending strong cosmic censorship to perturbations of highly charged Reissner-Nordstrom de Sitter spacetimes reveals the linear stability of the Cauchy horizon can be determined from the spectral gap of quasinormal modes, but becomes more complex with nonlinear backreaction. Confusion in literature arises from the subtleties involved in deriving conclusions about SCC violations from available numerical simulations, especially concerning near extremal RNdS black hole spacetimes where existing codes may be insufficient.