Ritabrata Biswas

The generalized second law of thermodynamics and the nature of the entropy function

In black-hole physics, the second law of thermodynamics is generally valid whether the black hole is a static or a non-static one. Considering the universe as a thermodynamical system the second law of black-hole dynamics extends to the non-negativity of the sum of the entropy of the matter and the horizon, known as generalized second law of thermodynamics (GSLT). Here, we have assumed the universe to be bounded by the event horizon where Bekenstein entropy-area relation and Hawking-temperature are not applicable. Thus considering entropy to be an arbitrary function of the area of the event horizon, we have tried to find the nature of the entropy function for the validity of the GSLT both in the quintessence era and in the phantom era. Finally, some graphical representation of the entropy function has been presented.

FRW Cosmological Model with Modified Chaplygin Gas and Dynamical System

The Friedmann-Robertson-Walker (FRW) model with dynamical Dark Energy (DE) in the form of modified Chaplygin gas (MCG) has been investigated. The evolution equations are reduced to an autonomous system on the two dimensional phase plane and it can be interpreted as the motion of the particle in an one dimensional potential. Also the dynamical system analysis has been extended to examine the critical points at infinity with will exist provided the equation of state parameter

Thermodynamics of Lema \(\hat{i}\) tre−Tolman−Bondi Model

\omega<-\frac{1}{3}

Presence of dark energy and dark matter: does cosmic acceleration signifies a weak gravitational collapse?

. Finally, theoretical points are asymptotically stable or unstable.

Gravitational collapse in generalized Vaidya space-time for Lovelock gravity theory

Here we consider our universe as inhomogeneous spherically symmetric Lema

Cosmological evolution across phantom crossing and the nature of the horizons

{\hat{i}}

A new proposal for Galactic dark matter: Effect of f(T) gravity

tre−Tolman−Bondi Model and analyze the thermodynamics of this model of the universe. The trapping horizon is calculated and is found to coincide with the apparent horizon. The Einstein field equations are shown to be equivalent with the unified first law of thermodynamics. Finally assuming the first law of thermodynamics validity of the generalized second law of thermodynamics is examined at the apparent horizon for the perfect fluid and at the event horizon for holographic dark energy.

Exact interior solutions in 2+1-dimensional spacetime

In this work the collapsing process of a spherically symmetric star, made of dust cloud, in the background of dark energy is studied for two different gravity theories separately, i.e., DGP Brane gravity and Loop Quantum gravity. Two types of dark energy fluids, namely, Modified Chaplygin gas and Generalised Cosmic Chaplygin gas are considered for each model. Graphs are drawn to characterize the nature and the probable outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different gravity theories. It is found that in case of dark matter, there is a great possibility of collapse and consequent formation of Black hole. In case of dark energy possibility of collapse is far lesser compared to the other cases, due to the large negative pressure of dark energy component. There is an increase in mass of the cloud in case of dark matter collapse due to matter accumulation. The mass decreases considerably in case of dark energy due to dark energy accretion on the cloud. In case of collapse with a combination of dark energy and dark matter, it is found that in the absence of interaction there is a far better possibility of formation of black hole in DGP brane model compared to Loop quantum cosmology model.