MG15 - Talk detail

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In this talk I will explore the consequences of the gravity-thermodynamics connection for an arbitrary null surface and highlight the thermodynamic significance of various geometrical quantities. In particular, I will demonstrate that: (a) A conserved current, associated with the time development vector in a natural fashion, has direct thermodynamic interpretation when evaluate on null surfaces. (b) Three different projections of a suitably defined gravitational momentum related to an arbitrary null surface in the spacetime lead to three different equations, all of which have thermodynamic interpretation. The first one reduces to a Navier-Stokes equation for the transverse drift velocity. The second can be written as a thermodynamic identity TdS = dE + P dV. The third describes the time evolution of the null surface in terms of suitably defined surface and bulk degrees of freedom. The implications will be discussed.

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Strong field gravitational lensing in the context of both higher spacetime dimensions and in presence of Kalb-Ramond field have been studied. After developing proper analytical tools to analyze the problem we consider gravitational lensing in three distinct black hole spacetimes --- (a) four dimensional black hole in presence of Kalb-Ramond field, (b) brane world black holes with Kalb-Ramond field and finally (c) black hole solution in f(T) gravity. In all the three situations we have depicted the behavior of three observables: the asymptotic position approached by the relativistic images, the angular separation and magnitude difference between the outermost images with others packed inner ones, both numerically and analytically. Difference between these scenarios have also been discussed along with possible observational signatures.

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Continuum spectrum from black hole accretion disc holds enormous information regarding the strong gravity regime around the black hole and hence about the nature of gravitational interaction in extreme situations. To explore them I will discuss effects of these alternative theories on the black hole continuum spectrum in an explicit manner. In the scenarios under consideration we have shown that there can be signatures sculptured on the black hole continuum spectrum, distinct from the standard general relativistic scenario. Interestingly, all these models exhibit black hole solutions with tidal charge parameter which can become negative, in sharp contrast with the situation in general relativity. Using the observational data of optical luminosity for eighty Palomer Green quasars we have illustrated that the difference between the theoretical estimates and the observational results gets minimized for negative values of the tidal charge parameter, signaling the possibility of higher dimensions or, scalar hair at play in those high gravity regimes.

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Yes

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In this talk I will discuss the evolution equation for gravitational perturbation in four dimensional spacetime in presence of a spatial extra dimension. The evolution equation is derived by perturbing the effective gravitational field equations on the four dimensional spacetime, which inherits non-trivial higher dimensional effects. The four dimensional gravitational perturbation now admits massive propagating degrees of freedom, courtesy to the existence of higher dimensions. Surprisingly, it turns out that the massive modes experience much smaller damping compared to the massless modes in general relativity and may even dominate over and above the general relativity contribution if one observes the ring down phase of a black hole merger event at sufficiently late times. Furthermore, the whole analytical framework has been supplemented by the fully numerical Cauchy evolution problem as well, which matches very well with the quasi-normal mode computation. The implications will also be discussed.

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Session

Accepted

Yes

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Time

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Abstract

I will analyze the emission pattern of a (fundamentally quantum) black hole in Kerr-Newman family in a model insensitive fashion. We demonstrate that, irrespective of the fundamental quantum theory, a macroscopic black hole always has non-continuously separated mass states, therefore they descend down in discrete manner. The evaluation of the step size reveals a universal relation between the dynamic and kinematic length scales for all black holes belonging to the Kerr-Newman family. This relation is basically made out of low energy parameters associated with a macroscopic black hole, but also reveals the parameters involved in the ultraviolet theory of it. I will also argue the independence of these features from the spacetime dimensions.

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