Showing papers by "Mubasher Jamil published in 2014"
TL;DR: Zahrani et al. as discussed by the authors investigated the conditions under which a charged particle can escape from the gravitational field of the Schwarzschild black hole after colliding with another particle, and the effective potential and escape velocity of the charged particle with angular momentum in the presence of the magnetic field was analyzed.
Abstract: The dynamics of a charged particle moving around a slowly rotating Kerr black hole in the presence of an external magnetic field is investigated. We are interested in exploring the conditions under which the charged particle can escape from the gravitational field of the black hole after colliding with another particle. The escape velocity of the charged particle in the innermost stable circular orbit is calculated. The effective potential and escape velocity of the charged particle with angular momentum in the presence of the magnetic field is analyzed. This work serves as an extension of a preceding paper dealing with the Schwarzschild black hole (Zahrani et al., Phys Rev D 87:084043, 2013).
71 citations
TL;DR: In this article, a non-commutative solution for static wormholes in f(R) gravity with a noncommutativity-geometry background is discussed. But the exact solution is not discussed.
Abstract: This paper discusses several new exact solutions for static wormholes in f(R) gravity with a noncommutative-geometry background. In the first part of the paper, we assume the power-law form f(R) = aRn and discuss several solutions corresponding to different values of the exponent. The second part of the paper assumes a particular form of the shape function that also yields a viable solution. This investigation generalizes some of our previous work in f(R) gravity, as well as in noncommutative geometry.
65 citations
TL;DR: In this paper, the authors derived exact solutions of static wormholes in f(R) gravity supported by the matter possesses Lorentzian density distribution of a particle-like gravitational source.
Abstract: In this paper, we derive some new exact solutions of static wormholes in f(R) gravity supported by the matter possesses Lorentzian density distribution of a particle-like gravitational source. We derive the wormhole’s solutions in two possible schemes for a given Lorentzian distribution: assuming an astrophysically viable F(R) function such as a power-law form and discuss several solutions corresponding to different values of the exponent (here $F =\frac{df}{dR}$
). In the second scheme, we consider particular form of two shape functions and have reconstructed f(R) in both cases. We have discussed all the solutions with graphical point of view.
61 citations
TL;DR: In this paper, the evolution of primordial black holes within the context of loop quantum cosmology is studied. But it is not shown that accretion of radiation does not affect the evolution.
Abstract: In this work, we study the evolution of primordial black holes within the context of loop quantum cosmology. First we calculate the scale factor and energy density of the Universe for different cosmic era and then taking these as inputs, we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum cosmology. We also conclude that due to slow variation of scale factor, the upper bound on initial mass fraction of presently evaporating PBHs are much greater in loop quantum cosmology than the standard case.
10 citations
TL;DR: In this article, the innermost stable circular orbit (ISCO) of a neutral and a charged particle around a static and spherically symmetric black hole in the presence of quintessence matter and external magnetic field was investigated.
Abstract: We investigate the dynamics of a neutral and a charged particle around a static and spherically symmetric black hole in the presence of quintessence matter and external magnetic field. We explore the conditions under which the particle moving around the black hole could escape to infinity after colliding with another particle. The innermost stable circular orbit (ISCO) for the particles are studied in detail. Mainly the dependence of ISCO on dark energy and on the presence of external magnetic field in the vicinity of black hole is discussed. By using the Lyapunov exponent, we compare the stabilities of the orbits of the particles in the presence and absence of dark energy and magnetic field. The expressions for the center of mass energies of the colliding particles near the horizon of the black hole are derived. The effective force on the particles due to dark energy and magnetic field in the vicinity of black hole is also discussed.
9 citations
TL;DR: In this paper, a collision of particles in the inner stable circular orbit is considered and the conditions for the escape of colliding particles from the vicinity of black hole are given. And the trajectories of the escaping particle are discussed.
Abstract: Considering the geometry of Reissner-Nordstrom (RN) black hole immersed in magnetic field we have studied the dynamics of neutral and charged particles. A collision of particles in the inner stable circular orbit is considered and the conditions for the escape of colliding particles from the vicinity of black hole are given. The trajectories of the escaping particle are discussed. Also the velocity required for this escape is calculated. It is observed that there are more than one stable regions if magnetic field is present in the accretion disk of black hole so the stability of ISCO increases in the presence of magnetic field. Effect of magnetic field on the angular motion of neutral and charged particles is observed graphically.
8 citations
TL;DR: In this article, a generalized version of the holographic dark energy model is considered, with a varying parameter, n, which evolves slowly with time, and the authors obtain the differential equation describing evolution of the dark energy density parameter, $\Omega_d$, for the flat and non-flat FRW universes.
Abstract: We consider a holographic dark energy model, with a varying parameter, n, which evolves slowly with time. We obtain the differential equation describing evolution of the dark energy density parameter, $\Omega_d$, for the flat and non-flat FRW universes. The equation of state parameter in this generalized version of holographic dark energy depends on n.
7 citations
TL;DR: In this article, the authors investigated the non-static Lorentzian wormhole model in the presence of anisotropic pressure and presented exact solutions of the Einstein field equations for the case of a dynamical wormhole.
Abstract: We have investigated the non-static Lorentzian Wormhole model in presence of anisotropic pressure. We have presented some exact solutions of Einstein equations for anisotropic pressure case. Introducing two EoS parameters we have shown that these solutions give very rich dynamics of the universe yielding to the different expansion history of it in the r - direction and in the T - direction. The corresponding explicit forms of the shape function b(r) is presented.We have shown that the Einstein’s field equations and unified first law are equivalent for the dynamical wormhole model. The first law of thermodynamics has been derived by using the Unified first law. The physical quantities including surface gravity and the temperature are derived for the wormhole. Here we have obtained all the results without any choice of the shape function. The validity of generalized second law (GSL) of thermodynamics has been examined at apparent and event horizons for the evolving Lorentzian wormhole.
6 citations
TL;DR: In this article, the motion of a neutral particle in the vicinity of a slowly rotating black hole in the Horava-Lifshitz theory of gravity and 3+1 dimensional topological Lifshitz black hole is investigated.
Abstract: The motion of a neutral particle in the vicinity of a slowly rotating black hole in the Horava-Lifshitz theory of gravity and 3+1 dimensional topological Lifshitz black hole is investigated. Geodesics for radial motion of the particles are also plotted. Some different cases of the orbital motion of the particle are discussed where maximum and minimum values of the effective potential are calculated. Further the Banados, Silk and West (BSW) mechanism is studied for these black holes. It is shown that the centre-of-mass energy (CME) of two colliding uncharged particles at the horizon of these black holes remains finite. Thus the BSW effect cannot be seen in these cases.
3 citations
Posted Content•
12 Feb 2014TL;DR: In this article, the authors investigated the dynamics of a charged particle moving around a slowly rotating Kerr black hole immersed in an external magnetic field due to the plasma in the accretion disc in the vicinity of the black hole.
Abstract: We investigate the dynamics of a charged particle moving around a slowly rotating Kerr black hole immersed in an external magnetic field due to the plasma in the accretion disc in the vicinity of the black hole. We are interested to explore the conditions under which the charged particle moving around a magnetized black hole can collide with another neutral particle or photon coming toward the black hole and can escape to infinity. We calculate escape velocity of the charged particle moving in the innermost stable circular orbit when it is hit by another neutral particle and discuss its behaviour. We also analyse the effective potential and escape velocity of the charged particle with angular momentum, in the presence of magnetic field. In general, we found that the motion of the particle moving in the vicinity of slowly rotating Kerr black hole immersed in a magnetic field cannot be predicted. However, by imposing the assumptions that particle is moving in the equatorial plane and its angular momentum and radial velocity does not change after collision we can predict the motion. This work is an extension of an earlier work which dealt with the Schwarzschild black hole (Zahrani et al, Phys. Rev. D 87, 084043 (2013)).