Generalized second law and entropy bound for a Reissner- Nordstr\"om black hole

It has been conjectured that black hole interacting with its surroundings will obey the Generalized Second Law ($GSL$) of thermodynamics. Conservation of $GSL$ is due to the fully thermal nature of Hawking radiation and an upper bound on entropy. We study these aspects for a Reissner-Nordstr$\ddot{\textbf{o}}$m ($RN$)black hole and conjecture that $GSL$ may be conserved if the equation of state of radiation near the horizon is modified. An upper bound on $S/E$, similar to the Bekenstein form evolves in the calculation.Comment: 11 page

Thermodynamics and Spectroscopy of charged Dilaton black holes

The Bohr-Sommerfeld quantization rule is useful to study the area spectrum of black holes by employing adiabatic invariants. This method is extended to charged dilaton black holes in 2+1 dimensions. We put the background space-time into the Kruskal-like coordinate to find the period with respect to Euclidian time. Also assuming that the adiabatic invariant obeys Bohr-Sommerfeld quantization rule, detailed study of area and entropy spectrum has been done. It is dependent on the charge and is equally spaced as well. We also investigate the thermodynamics of the charged dilaton black hole.Comment: 10 pages and 3 figures; accepted in "General Relativity and Gravitation"(GRG). arXiv admin note: text overlap with arXiv:1204.1786, arXiv:1203.5947 by other author

Dirac Quasinormal modes of MSW black holes

In this paper we study the Dirac quasinormal modes of an uncharged 2 + 1 black hole proposed by Mandal et. al and referred to as MSW black hole in this work. The quasi- normal mode is studied using WKB approximation method. The study shows that the imaginary part of quasinormal frequencies increases indicating that the oscillations are damping and hence the black hole is stable against Dirac perturbations.Comment: 8 page, 3 figure, Appear in MPL

Absorption cross section of RN black hole

The behavior of a charged scalar field in the RN black hole space time is studied using WKB approximation. In the present work it is assumed that matter waves can get reflected from the event horizon. Using this effect, the Hawking temperature and the absorption cross section for RN black hole placed in a charged scalar field are calculated. The absorption cross section $\sigma _{abs}$ is found to be inversely proportional to square of the Hawking temperature of the black hole.Comment: 6 pages, 2 figure

First Order Phase Transitions in a Bianchi type-I universe

Considering the theory of induced gravity coupled to matter fields, taking the $\phi ^6$ interaction potential model we evaluate the one-loop effective potential in a (3+1)dimensional Bianchi type-I spacetime. It is proved that the $\phi ^6$ theory can be regularised in (3+1)dimensional curved spacetime. We evaluate the finite temperature effective potential and study the temperature dependence of phase transitions. The nature of phase transitions in the early universe is clarified to be of first order. The effects of spacetime curvature and arbitrary field coupling on the phase transitions in the early universe are also discussed.Comment: 20 pages, 7 figures, To appear in Physical Rev.

Area spectrum and thermodynamics of KS black holes in Ho\v{r}ava gravity

We investigate the area spectrum of Kehagias-Sfetsos black hole in Ho\v{r}ava-Lifshitz gravity via modified adiabatic invariant $I=\oint p_i d q_i$ and Bohr-Sommerfeld quantization rule. We find that the area spectrum is equally spaced with a spacing of $\Delta A=4 \pi l_p ^2$. We have also studied the thermodynamic behavior of KS black hole by deriving different thermodynamic quantities.Comment: 9 pages, 3 figures. Gen Relativ Gravit 201

Late-time evolution of Dirac field around Schwarzschild-quintessence black hole

The late-time evolution of Dirac field around spherically symmetric black hole surrounded by quintessece is studied numerically. Our results show, for lower values of the quintessence state parameter \epsilon, Dirac field decays as power-law tail but with a slower decay rate than the corresponding Schwarzschild case. But for \epsilon<-1/3, all the \ell-poles of the Dirac field give up the power-law decay form and relax to a constant residual field at asymptotically late times. The value of this residual field for which the field settles down varies on different surfaces. It has the lowest value on the black hole event horizon, increases as the radial distance increases and maximizes on the cosmological horizon.Comment: 10 pages, 5 figures. To appear in MPLA. arXiv admin note: text overlap with arXiv:1210.047

Data Analysis of Massive Gravitational Waves from Gamma Ray Bursts

We investigate the detectability of massive mode of polarization of Gravitational Waves (GWs) in f(R) theory of gravity associated with Gamma Ray Bursts (GRBs) sources. We obtain the beam pattern function of Laser Interferometric Gravitational wave Observatory (LIGO) corresponding to the massive polarization of GWs and perform Bayesian analysis to study this polarization. It is found that the massive polarization component with a mass of 10^-22eV/c2 is too weak to be detected at LIGO with its current configuration.Comment: 17 pages, 4 figures, 2 tables, 51 references Accepted for publication in International Journal of Modern Physics

A Mond Programme from Einstein Hilbert Action

In the usual derivation of Einstein's equation from action, the surface terms are neglected. Hawking \cite{hw} gave a derivation of the gravitational Hamiltonian keeping all surface terms. Using such surface terms Easson et.al.\cite{ea} showed that Friedmann equation could get modified and using the modified Friedmann equation they could explain the cosmic acceleration. We study the effect of surface terms on a galactic scale and find that the classical limit of the modified Friedmann equation will lead to a MOND like acceleration term.Comment: 5 page

Late time tails of fields around Schwarzschild black hole surrounded by quintessence

The evolution of scalar, electromagnetic and gravitational fields around spherically symmetric black hole surrounded by quintessence are studied with special interest on the late-time behavior. In the ring down stage of evolution, we find in the evolution picture that the fields decay more slowly due to the presence of quintessence. As the quintessence parameter \epsilon decreases, the decay of l=0 mode of scalar field gives up the power-law form of decay and relaxes to a constant residual field at asymptotically late times. The l>0 modes of scalar, electromagnetic and gravitational fields show a power-law decay for large values of \epsilon, but for smaller values of \epsilon they give way to an exponential decay.Comment: 15 pages, 13 figures. Accepted for publication in Gen. Relativ. Gra