arXiv subjects

Yen-Kheng Lim

Publications and source records attributed to Yen-Kheng Lim.

39 records · Page 3Linked to original sources

arXiv2015

Motion of charged particles around a magnetized/electrified black hole

Geodesic equations of timelike and null charged particles in the Ernst metric are studied. We consider two distinct forms of the Ernst solution where the Maxwell potential represents either a uniform electric or magnetic field. Circular orbits in various configurations are considered, as well as their perturbations and stability. We find that the electric field strength must be below a certain charge-dependent critical value for these orbits to be stable. The case of the magnetic Ernst metric contains a limit which reduces to the Melvin magnetic universe. In this case the equations of motion are solved to reveal cycloidlike or trochoidlike motion, similar to those found by Frolov and Shoom around black holes immersed in test magnetic fields.

gr-qc↗

arXiv2014

Geodesic motion in the vacuum C-metric

Geodesic equations of the vacuum C-metric are derived and solved for various cases. The solutions describe the motion of timelike or null particles with conserved energy and angular momentum. Polar, nearly-circular orbits around weakly accelerated black holes may be regarded as a perturbation of circular Schwarzschild geodesics. Results indicate that circular Schwarzschild geodesics of radius $r_0>6m$ are stable under small uniform accelerations along the orbital plane. These stable orbits undergo small oscillations around $r_0$, behaving like a harmonic oscillator driven by a periodic force plus another constant force. Circular orbits with axis parallel to the direction of black hole acceleration are also considered. In this case an algebraic relation expressing the condition of stability is obtained. This refines the stability analysis done in previous literature. We also present an analysis of radial geodesics along the poles. There exist a solution where a particle remains at unstable equilibrium at a fixed distance directly behind the accelerating black hole. Examples of numerical solutions are presented for other more general cases.

gr-qc↗

arXiv2012

Warped branches of flux compactifications

We consider Freund-Rubin-type compactifications which are described by (p+q)-dimensional Einstein gravity with a positive cosmological constant and a q-form flux. Using perturbative expansions of Kinoshita's ansatz for warped dS_pxS^q and AdS_pxS^q spacetimes, we obtain analytical solutions describing the warped branches and their respective phase spaces. These equations are given by inhomogeneous Gegenbauer differential equations which can be solved by the Green's function method. The requirement that the Green's functions are regular provides constraints which determine the structure of the phase space of the warped branches. We apply the perturbation results to calculate the thermodynamic variables for the warped dS_pxS^q branch. In particular, the first law of thermodynamics can be reproduced using this method.

gr-qc↗