Seventeenth Marcel Grossmann Meeting

Session

Black holes in alternative theories of gravity

BH2

8 Jul 2024, 15:00

Aurum, the ‘Gabriele d’Annunzio’ University and ICRANet

Conveners

Black holes in alternative theories of gravity: Monday block 1

• Jutta Kunz (University of Oldenburg)
• Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)

Black holes in alternative theories of gravity: Monday block 2

• Jutta Kunz (University of Oldenburg)
• Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)

Black holes in alternative theories of gravity: Friday block 1

• Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)
• Jutta Kunz (University of Oldenburg)

Black holes in alternative theories of gravity: Friday block 2

• Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)
• Jutta Kunz (University of Oldenburg)

Description

Black holes are excellent probes to study strong gravitational fields and thus to test Einstein's theory of general relativity and its contenders by comparing their predictions with observations. Alternative theories of gravity may lead to distinctive features for black holes, which include their multipoles, quasi-normal modes or shadows.

175. Observing naked singularities by the Event Horizon Telescope

Dr Petya Nedkova (Sofia University)

08/07/2024, 15:00

Black holes in alternative theories of gravity

Talk in a parallel session

Horizonless compact objects may produce phenomenological features which distinguish them observationally from black holes. In particular, the images of the accretion disks around them possess a characteristic morphology including a series of central bright rings instead of a black hole shadow. We demonstrate how the central ring structure arises relating it to the behavior of the deflection...

146. Distinguishing Signature of Kerr-MOG Black Hole and Naked Singularity via Lense-Thirring Effect

PARTHA PRATIM PRADHAN (HIRALAL MAZUMDAR MEMORIAL COLLEGE FOR WOMEN)

08/07/2024, 15:30

Black holes in alternative theories of gravity

Talk in a parallel session

We examine the geometrical difference between non-extremal black hole(NXBH), extremal black hole(XBH) and naked singularity(NS) via Lense-Thirring(LT) effect in spinning modified-gravity(MOG). For NXBH, we find that the LT frequency (${\mathrm{\Omega }}_{LT}$) is proportional to the angular-momentum($J=a\mathcal{M}$) parameter or spin parameter($a$) i.e. ${\mathrm{\Omega }}_{LT}\propto J$ or $\Omega_{LT}\propto a...

29. Black hole thermodynamics and boundary terms

Marek Liška (Institute of Theoretical Physics, Charles University, Prague)

08/07/2024, 15:50

Black holes in alternative theories of gravity

Talk in a parallel session

I discuss sensitivity of black hole thermodynamics to certain boundary terms in the action. While boundary terms cannot affect the classical gravitational dynamics, they apparently influence both the black hole entropy and temperature. Remarkably, this behaviour is confirmed by two standard approaches to black hole thermodynamics; the covariant phase space (Iyer-Wald) and the Euclidean...

51. Some words about gravitational entropy and Penrose's Weyl curvature conjecture

Daniele Gregoris (Jiangsu University of Science and Technology)

08/07/2024, 16:10

Black hole thermodynamics

Talk in a parallel session

Many notions of entropy have been formulated in Physics, from thermodynamics to statistical mechanics and information theory. Bekenstein and Hawking, relying on completely different physical arguments than each other's, pioneered the idea of gravitational entropy claiming that the gravitational field of an empty space
black hole as Schwarzschild comes with an entropy equal to one fourth of...

177. Black holes in a modified gravity: Hawking radiation and cosmological implications

Banibrata Mukhopadhyay (Indian Institute of Science)

08/07/2024, 17:00

Black holes in alternative theories of gravity

Talk in a parallel session

There are observations supporting the plausible modification to Einstein
gravity, while the exact theory of gravity in the strong field regime is
indeed under debate. We obtain a new black hole solution in an f(R)-gravity-based
modified gravity. Such a black hole evaporates faster by Hawking radiation
compared to that in the Einstein gravity, i.e. the Kerr black hole.
One of its...

500. Hairy black holes in extended Einstein-Maxwell-scalar theories with magnetic charge and kinetic couplings

Mr Kitaro Taniguchi (Tokyo University of Science)

08/07/2024, 17:20

Black holes in alternative theories of gravity

Talk in a parallel session

We study static and spherically symmetric black hole (BH) solutions in extended Einstein- Maxwell-scalar theories which is classified in a subclass of the $U(1)$ gauge-invariant scalar-vector- tensor theories. The scalar field is coupled to the vector field, which has electric and magnetic charges. We investigate modifications to the Reissner-Nordstr ̈om solution focusing on the three types of...

114. Strong interactions and Bekenstein – Hawking black hole entropy

Hristu Culetu

08/07/2024, 17:40

Black holes in alternative theories of gravity

Talk in a parallel session

All particles created through the Hawking process have to be generated in the collapsing object. The black hole internal states should be related to the precollapsed state (a one-to-one correspondence between the internal state and precollapse configuration).
The baryons that formed the initial collapsing star cannot reappear since all their rest energy has been carried away by the thermal...

67. How Relic Black Holes , in the early universe allow Torsion to form a Cosmological constant, and set restrictions on Relic Black holes in terms of a quantum number n as specified

Andrew Beckwith (Chongqing University, physics)

08/07/2024, 18:00

Black holes in alternative theories of gravity

Talk in a parallel session

Our idea is to state that a particular set of values and reformulation of initial conditions for relic black holes, as stated in this manuscript , will enable using the idea of Torsion to formulate a cosmological constant and resultant Dark Energy. Relic Planck sized black holes will allow for a spin density term which presents an opportunity to modify a brilliant argument given as to...

82. The Classical Point Particle Singularity: An Illusion in GR and Elsewhere!

Yousef Sobouti (Institute for Advanced Studies in Basic Sciences - Zanjan)

08/07/2024, 18:20

Black holes in alternative theories of gravity

Talk in a parallel session

Singularities in Newton's gravity, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill conceived assumptions that, a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-like entities can be assigned precise coordinates and momenta. In the case of GR, we...

615. Quasinormal modes of rapidly rotating black holes

Fech Scen Khoo

12/07/2024, 15:00

Black holes in alternative theories of gravity

Invited talk in a parallel session

We present the spectrum of quasinormal modes of rapidly rotating black holes. We apply a spectral decomposition on the perturbations of the metric and other dynamical fields. We compare our results with the modes computed using other methods, study the accuracy of our calculations, and investigate the application of our method to black holes in alternative theories of gravity.

386. Black holes at a crossroads during the late stages of evaporation in quadratic gravity

Samuele Marco Silveravalle (SISSA)

12/07/2024, 15:30

Black hole thermodynamics

Talk in a parallel session

By studying quantum fields on classical curved spacetimes, Gibbons and Hawking managed to derive the thermodynamical properties of black holes, while making at the same time the first robust prediction of a semiclassical theory of gravity. Nevertheless, they quickly realized that black hole evaporation leads to sudden bursts of energy and loss of information. It can be argued that these...

333. The canonical ensemble of a self-gravitating matter thin shell in asymptotically AdS

Tiago Fernandes (IST, CENTRA, GRIT)

12/07/2024, 15:50

Black hole thermodynamics

Talk in a parallel session

We construct the canonical ensemble of a matter thin shell in
asymptotically AdS using the Euclidean path integral approach.
We impose spherical symmetry, the Hamiltonian and momentum constraints,
the hot AdS regularity conditions and the asymptotic behaviour of AdS
on the metrics summed in the path integral and obtain the reduced action,
which can be regarded as a generalized free...

471. Embeding LTB models in mimetic gravity and exact spherically symmetric solutions

Hongguang Liu (FAU Erlangen-Nürnberg)

12/07/2024, 16:10

Black holes in alternative theories of gravity

Talk in a parallel session

In this talk we present the analysis of a large class of extended mimetic gravity Lagrangians, which allow the embedding of the Lemaître-Tolman-Bondi (LTB) models in spherically symmetric spacetimes. Using the LTB embedding, we are able to completely decouple the dynamics along the radial direction and obtain exact solutions of the modified Friedmann equations. Moreover, we introduce a...

83. Dynamics of scalar fields in the nonlinear $\sigma$-models in the Eddington inspired Born-Infeld gravity

Bakhodir Kayumov (School of Humanities and Natural Sciences, New Uzbekistan University)

12/07/2024, 17:00

Black holes in alternative theories of gravity

Talk in a parallel session

In our presentation, we demonstrate the spacetime properties of a monopole within nonlinear $\sigma$-models in Eddington inspired Born-Infeld gravity. Specifically, we investigate characteristic circular orbits of test particles and photons, including circular null geodesics, marginally bound orbits, and stable circular orbits, as influenced by spacetime parameters. Additionally, we discuss...

345. Regular multi-horizon Lee-Wick black holes

Nicolò Burzillà (INFN, Rome 2 Tor Vergata)

12/07/2024, 17:15

Black hole thermodynamics

Talk in a parallel session

We present a detailed analysis of the static spherically symmetric solutions of a sixth-derivative gravity model with complex conjugate poles ( Lee-Wick gravity ) in the effective delta source approximation. The solutions exhibit an interesting structure that depends on the real and imaginary part of the Lee-Wick mass $\mu =a+ib$. In particular, because of the oscillating behavior of the...

563. Holography of new 3d conformal higher spin theories for low spins

Iva Lovrekovic (TU Wien)

12/07/2024, 17:30

Black holes in alternative theories of gravity

Talk in a parallel session

We study asymptotic symmetries for 3d Chern-Simons theory as a gauge theory of so(3,2), sl_4 and sl_5 algebras. For the near horizon boundary conditions we present solutions from several projectors from Chern-Simons to the metric formulation. These solutions are generalized BTZ solutions for our theories. We also study the classification according to so(3,2) one parameter subgroups and...

197. Does no-hair theorem fail in the modified theories of gravity?

Semin Xavier (IIT Bombay)

12/07/2024, 17:45

Black holes in alternative theories of gravity

Talk in a parallel session

The no-hair conjecture asserts that all black holes in general relativity (GR) coupled to any matter must be Kerr–Newman type. The three independent externally observable classical parameters— mass, electric charge, and angular momentum — uniquely determine all the information about the matter that formed into a black hole. However, the conjecture fails in some cases where the matter sources...

274. Scalarized Black Hole Solutions in Modified Theories

Zakaria Belkhadria (Università di Cagliari/ Université de Genève/ INFN/GWSC)

12/07/2024, 18:00

Black holes in alternative theories of gravity

Talk in a parallel session

This presentation delves into the study of 'hairy' black holes within the framework of Einstein scalar Maxwell gravity and Einstein scalar Gauss-Bonnet theories, with a focus on revealing new scalarized black hole solutions. We revisit established scalarization phenomena and venture into new solution territories, particularly highlighting the blend of linear and non-linear scalarization in...

407. Testing alternative spacetimes by fitting both the hot-spot data of Sgr A*, and high-frequency quasi-periodic oscillations observed in AGNs and microquasars

Misbah Shahzadi (COMSATS University Islamabad, Pakistan)

12/07/2024, 18:15

Black holes in alternative theories of gravity

Talk in a parallel session

We explore the class of stationary, axisymmetric, and asymptotically flat spacetimes describing charged black holes in general relativity combined with nonlinear electrodynamics, or reflecting the influence of dark matter, or in so-called parameterized dirty Kerr spacetimes, and test them using the observational data of both hot-spot and the high-frequency quasi-periodic oscillations detected...

10. Banados-Silk-West effect with finite forces near different types of horizons: general classification of scenarios

Oleg Zaslavskii (Kharkov V. N. Karazin National University)

Black holes in alternative theories of gravity

Talk in a parallel session

If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy Ec.m. in the center of mass frame can grow unbounded. This is the Banados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. We study this effect in a more general context, when both geometric...