Conveners
Black holes in alternative theories of gravity: Monday block 1
- Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)
- Jutta Kunz (University of Oldenburg)
Black holes in alternative theories of gravity: Monday block 2
- Jose Luis Blázquez-Salcedo (Universidad Complutense de Madrid)
- Jutta Kunz (University of Oldenburg)
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.
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...
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 ($\Omega_{LT}$) is proportional to the angular-momentum($J=a\,{\cal M}$) parameter or spin parameter($a$) i.e. $\Omega_{LT}\propto J $ or $\Omega_{LT}\propto a...
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...
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...
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...
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...
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...
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...
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...
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.
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...
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...
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...
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...
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 $\mu=a +i b$. In particular, because of the oscillating behavior of the...
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...
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...
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...
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...
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...
