Innermost stable circular orbits of charged spinning test particles

The effects of a paritcle's spin and electric charge on its angular momentum, energy and radius on the innermost stable circular orbit are investigated based on the particle's equations of motion in a background of the Kerr-Newmann spacetime. It is found that the particle's angular momentum and energy have monotonous relationships with not only its spin but also its charge; it is also discovered that the spinning particle's radius may change non-monotonously with its charge. Hence, our result remarkably indicates that particles owning identical spin but different charge may degenerate into a same last stable circular orbit.Comment: 6 page

Observational constraint on the interacting dark energy models including the Sandage-Loeb test

Two types of interacting dark energy models are investigated using the type Ia supernova (SNIa), observational $H(z)$ data (OHD), cosmic microwave background (CMB) shift parameter and the secular Sandage-Loeb (SL) test. We find that the inclusion of SL test can obviously provide more stringent constraint on the parameters in both models. For the constant coupling model, the interaction term including the SL test is estimated at $\delta=-0.01 \pm 0.01 (1\sigma) \pm 0.02 (2\sigma)$, which has been improved to be only a half of original scale on corresponding errors. Comparing with the combination of SNIa and OHD, we find that the inclusion of SL test directly reduces the best-fit of interaction from 0.39 to 0.10, which indicates that the higher-redshift observation including the SL test is necessary to track the evolution of interaction. For the varying coupling model, we reconstruct the interaction $\delta (z)$, and find that the interaction is also negative similar as the constant coupling model. However, for high redshift, the interaction generally vanishes at infinity. The constraint result also shows that the $\Lambda$CDM model still behaves a good fit to the observational data, and the coincidence problem is still quite severe. However, the phantom-like dark energy with $w_X<-1$ is slightly favored over the $\Lambda$CDM model.Comment: 10 pages, 7 figure

Holographic thermalization with a chemical potential in Gauss-Bonnet gravity

Holographic thermalization is studied in the framework of Einstein-Maxwell-Gauss-Bonnet gravity. We use the two-point correlation function and expectation value of Wilson loop, which are dual to the renormalized geodesic length and minimal area surface in the bulk, to probe the thermalization. The numeric result shows that larger the Gauss-Bonnet coefficient is, shorter the thermalization time is, and larger the charge is, longer the thermalization time is, which implies that the Gauss-Bonnet coefficient can accelerate the thermalization while the charge has an opposite effect. In addition, we obtain the functions with respect to the thermalization time for both the thermalization probes at a fixed charge and Gauss-Bonnet coefficient, and on the basis of these functions, we obtain the thermalization velocity, which shows that the thermalization process is non-monotonic. At the middle and later periods of the thermalization process, we find that there is a phase transition point, which divides the thermalization into an acceleration phase and a deceleration phase. We also study the effect of the charge and Gauss-Bonnet coefficient on the phase transition point.Comment: 23 pages, many figures,footnote 4 is modified. arXiv admin note: substantial text overlap with arXiv:1305.484

Holographic thermalization in noncommutative geometry

Gravitational collapse of a shell of dust in noncommutative geometry is probed by the renormalized geodesic length, which is dual to probe the thermalization by the two-point correlation function in the dual conformal field theory. We find that larger the noncommutative parameter is, longer the thermalization time is, which implies that the large noncommutative parameter delays the thermalization process. We also investigate how the noncommutative parameter affects the thermalization velocity and thermalization acceleration.Comment: some materials have been delete