Showing papers by "Mubasher Jamil published in 2017"

Strong gravitational lensing by a charged Kiselev black hole

Abstract: We study the gravitational lensing scenario where the lens is a spherically symmetric charged black hole (BH) surrounded by quintessence matter. The null geodesic equations in the curved background of the black hole are derived. The resulting trajectory equation is solved analytically via perturbation and series methods for a special choice of parameters, and the distance of the closest approach to black hole is calculated. We also derive the lens equation giving the bending angle of light in the curved background. In the strong field approximation, the solution of the lens equation is also obtained for all values of the quintessence parameter $$w_q$$ . For all $$w_q$$ , we show that there are no stable closed null orbits and that corrections to the deflection angle for the Reissner–Nordstrom black hole when the observer and the source are at large, but finite, distances from the lens do not depend on the charge up to the inverse of the distances squared. A part of the present work, analyzed, however, with a different approach, is the extension of Younas et al. (Phys Rev D 92:084042, 2015) where the uncharged case has been treated.

Generalized second law of thermodynamic in modified teleparallel theory

Abstract: This study is conducted to examine the validity of the generalized second law of thermodynamics (GSLT) in flat FRW for modified teleparallel gravity involving coupling between a scalar field with the torsion scalar T and the boundary term $$B=2 abla _{\mu }T^{\mu }$$ . This theory is very useful, since it can reproduce other important well-known scalar field theories in suitable limits. The validity of the first and second law of thermodynamics at the apparent horizon is discussed for any coupling. As examples, we have also explored the validity of those thermodynamics laws in some new cosmological solutions under the theory. Additionally, we have also considered the logarithmic entropy corrected relation and discuss the GSLT at the apparent horizon.

Dynamics and center of mass energy of colliding particles around black hole in f(R) gravity

Abstract: We have investigated the dynamics of particles in the vicinity of a static spherically symmetric black hole in f(R) gravity. Using the Euler Lagrange method, the dynamical equations of a neutral particle are obtained. Assuming that the particle is initially moving in the innermost stable circular orbit (IMSCO), we have calculated its escape velocity, after a collision with some other particle. The conditions for the escape of colliding particles are discussed. The effective potential and the trajectories of the escaping particles are studied graphically.

Alternative approach to thermodynamic phase transitions.

Abstract: One of the major open problems in theoretical physics is a consistent quantum gravity theory.Recent developments in thermodynamic phase transitions ofblack holes and their van der Waals-like behavior may provide an interesting quantum interpretation of classical gravity. Studyingdifferent methods of investigating phase transitions can extend our insight into the nature of quantumgravity. In this paper, we present an alternative theoretical approach for finding thermodynamicphase transitions in the extended phase space. Unlike the standard methods based on the usualequation of state involving temperature, our approach usesa new quasi-equation constructed fromthe slope of temperature versus entropy. This approach addresses some of the shortcomings ofthe other methods, and provides a simple and powerful way of studying the critical behavior of athermodynamical system. Among the applications of this approach, we emphasize the analyticaldemonstration of possible phase transition points, and theidentification of the non-physical rangeof horizon radii for black holes.

Dynamics and center of mass energy of colliding particles around black hole in f(R) gravity

Abstract: We have investigated the dynamics of particles in the vicinity of a static spherically symmetric black hole in f(R) gravity. Using the Euler-Lagrange method the dynamical equations of a neutral particle are obtained. Assuming that the particle is initially moving in the innermost stable circular orbit, we have calculated its escape velocity, after a collision with some other particle. The conditions for the escape of colliding particles are discussed. The effective potential and the trajectories of the escaping particles are studied graphically.

A new prescription towards thermodynamic phase transition

Abstract: One of the serious open problems of theoretical physics is to find a consistent quantum gravity theory. Recent developments in thermodynamic phase transition of black holes and their van der Waals like behavior may provide an interesting quantum interpretation of classical gravity. Studying different methods for investigating phase transition can deepen our insight into the nature of quantum gravity. In this paper, we present a new theoretical prescription for finding out thermodynamic phase transition in the extended phase space. Unlike standard method of the usual equation of state which is according to temperature, our new prescription is based on a new typical equation of state which is originating from the slope of temperature versus entropy. This new prescription addresses some of the shortcomings of other usual methods and provides a simple powerful way for studying critical behavior of a thermodynamical system in more details. Among the achievements of the new prescription, we emphasize to addressing the problem of ensemble dependency, analytical demonstration of possible phase transition points and denoting the nonphysical range of horizon radius for the black holes.

Products of thermodynamic parameters of the generalized charged rotating black hole and the Reissner–Nordström black hole with a global monopole

Abstract: We investigate the thermodynamics of the Kerr–Newman–Kasuya black hole and the Reissner–Nordstrom black hole with a global monopole on inner and outer horizons. Products of surface gravities, surface temperatures, Komar energies, electromagnetic potentials, angular velocities, areas, entropies, horizon radii and irreducible masses at the Cauchy and event horizons are calculated. It is observed that the product of surface gravities, the surface temperature product and the product of Komar energies, electromagnetic potentials and angular velocities at horizons are not universal quantities for these black holes. Products of areas and entropies at the horizons are independent of black hole masses. The heat capacity is calculated for the generalized charged rotating black hole, and a phase transition is observed under certain conditions on r.

Rotating Black Hole in Asymptotically Safe Gravity Theory: Implications to Penrose Process and the Geodetic Precession

Abstract: A spherically symmetric rotating black hole solution in infra red (IR) limit of asymptotically safe gravity, containing higher derivative terms, is analyzed in this work. The involvement of a new parameter $\tilde{\xi}$ in this solution makes it different from Schwarzschild black hole. Its rotational counter part is constructed by employing the technique of Newman-Janis algorithm, along with the modification suggested by M. Azreg-Ain\"{o}u. The Killing horizon, event horizon and singularity of the computed metric is then discussed. It is noticed that the ergosphere is increased as $\tilde{\xi}$ increases. Considering the black hole solution in equatorial plane, the geodesics of particles, both null and time like cases, are explored. The effective potential is computed and graphically analyzed for different values of parameter $\tilde{\xi}$. The energy extraction from black hole is investigated via Penrose process. For the same values of spin parameter, the numerical results suggest that the efficiency of Penrose process is greater in asymptotically safe gravity than in Kerr Black Hole. At the end, a brief discussion on Lense-Thirring frequency is also done.