Nijo Varghese

Quasinormal modes of Reissner–Nördstrom black hole surrounded by quintessence

We evaluate the complex frequencies of the normal modes for the charged scalar field perturbations around a Reissner–Nördstrom black hole surrounded by a static and spherically symmetric quintessence using third order WKB approximation approach. Quintessence decreases the oscillation frequency and increases the damping time of quasinormal frequencies. We studied the variation of quasinormal frequencies with charge of the black bole, mass and charge of perturbing scalar field and the quintessential parameters.

The thermodynamics and thermodynamic geometry of the Park black hole

We study the thermodynamics and thermodynamic geometry of the Park black hole in Hořava gravity. By incorporating the ideas of differential geometry, we investigate the thermodynamics by using the Weinhold and the Ruppeiner geometry. We have also analyzed it in the context of the newly developed geometrothermodynamics (GTD). The divergence of the specific heat is associated with a second-order phase transition. Here in the context of the Park black hole, both Weinhold’s metric and Ruppeiner’s metric well explain this phase transition. But these explanations depend on the choice of the potential. Hence the Legendre invariant GTD is used, and with the true singularities in the curvature scalar, they well explain the second-order phase transition. All these methods together give an exact idea of all the behaviors of the Park black hole thermodynamics.

Phase transition, quasinormal modes and Hawking radiation of Schwarzschild black hole in quintessence field

Black hole thermodynamic stability can be determined by studying the nature of heat capacity of the system. For Schwarzschild black hole the heat capacity is negative, but in the quintessence field, this system shows a second-order phase transition, implying the existence of a stable phase. We further discuss the equation of state of the present system. While analyzing the quasinormal modes (QNM), we find that the massive scalar QNM frequencies in the complex ω plane shows a dramatic change when we plot it as a progressive function of quintessence state parameter. We also find the Hawking temperature of the system via the method of tunneling.

Evolution of electromagnetic and Dirac perturbations around a black hole in Horava gravity

The evolution of electromagnetic and massless Dirac perturbations in the spacetime geometry of Kehagias–Sfetsos (KS) black hole in the deformed Hořava–Lifshitz (HL) gravity is investigated and the associated quasinormal modes (QNMs) are evaluated from time domain integration data. We find a considerable deviation in the nature of field evolution in HL theory from that in the Schwarzschild spacetime and QNM region extends over a longer time in HL theory before the power-law tail decay begins. The dependence of the field evolution on the HL parameter α is also studied. In the time domain picture we find that the length of QNM region increases with α. But the late-time decay of field follows the same power-law tail behavior as in the case of Schwarzschild black hole.

Thermodynamic geometry of Reissener-Nordström-de Sitter black hole and its extremal case

We study the thermodynamics and the different thermodynamic geometric methods of Reissener-Nordström-de Sitter black hole and its extremal case, which is similar to the de Sitter black hole coupled to a scalar field, rather called an MTZ black hole. While studying the thermodynamics of the systems, we could find some abnormalities. In both cases, the thermodynamic geometric methods could give the correct explanation for all abnormal thermodynamic behaviors in the system.

Evolution of massive fields around a black hole in Hořava gravity

We study the evolution of massive scalar field in the spacetime geometry of Kehagias-Sfetsos black hole in deformed Hořava-Lifshitz (HL) gravity by numerical analysis. We find that the signature of HL theory is encoded in the quasinormal mode (QNM) phase of the evolution of field. The QNM phase in the evolution process lasts for a longer time in HL theory. QNMs involved in the evolution of massive field are calculated and find that they have a higher oscillation frequency and a lower damping rate than the Schwarzschild spacetime case. We also study the relaxation of field in the intermediate and asymptotic range and verified that behaviors of field in these phases are independent of the HL parameter and is identical to the Schwarzschild case.

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

EFFECT OF COSMIC STRING IN SPHERICALLY SYMMETRIC BLACK HOLE ON THE DIRAC PERTURBATION

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