Yu-Xiao Liu

Localization of matters on pure geometrical thick branes

In the literatures, several types of thick smooth brane configurations in a pure geometric Weyl integrable 5-dimensional space time have been presented. The Weyl geometry is a non-Riemannian modification of 5-dimensional Kaluza-Klein (KK) theory. All these thick brane solutions preserve 4-dimensional Poincare invariance, and some of them break Z2-symmetry along the extra dimension. In this paper, we study localization of various matter fields on these pure geometrical thick branes, which also localize the graviton. We present the shape of the potential of the corresponding Schrodinger problem and obtain the lowest KK mode. It is shown that, for both spin 0 scalars and spin 1 vectors, there exists a continuum gapless spectrum of KK states with m2 > 0. But only the massless mode of scalars is found to be normalizable on the brane. However, for the massless left or right chiral fermion localization, there must be some kind of Yukawa coupling. For a special coupling, there exist a series of discrete massive KK modes with m2 > 0. It is also showed that for a given coupling constant only one of the massless chiral modes is localized on the branes.

Charged spinning black holes as Particle Accelerators

It has recently been pointed out that the spinning Kerr black hole with maximal spin could act as a particle collider with arbitrarily high center-of-mass energy. In this paper, we will extend the result to the charged spinning black hole, the Kerr-Newman black hole. The center-of-mass energy of collision for two uncharged particles falling freely from rest at infinity depends not only on the spin a but also on the charge Q of the black hole. We find that an unlimited center-of-mass energy can be approached with the conditions: (1) the collision takes place at the horizon of an extremal black hole; (2) one of the colliding particles has critical angular momentum; (3) the spin a of the extremal black hole satisfies (1/{radical}(3)){<=}(a/M){<=}1, where M is the mass of the Kerr-Newman black hole. The third condition implies that to obtain an arbitrarily high energy, the extremal Kerr-Newman black hole must have a large value of spin, which is a significant difference between the Kerr and Kerr-Newman black holes. Furthermore, we also show that, for a near-extremal black hole, there always exists a finite upper bound for center-of-mass energy, which decreases with the increase of the charge Q.

A note on Friedmann equation of FRW universe in deformed Horava-Lifshitz gravity from entropic force

With entropic interpretation of gravity proposed by Verlinde, we obtain the Friedmann equation of the Friedmann—Robertson—Walker universe for the deformed Hořava—Lifshitz gravity. It is shown that, when the parameter of Hořava—Lifshitz gravity ω → ∞, the modified Friedmann equation will go back to the one in Einstein gravity. This results may imply that the entropic interpretation of gravity is effective for the deformed Hořava—Lifshitz gravity.

Bulk matters on symmetric and asymmetric de Sitter thick branes

An asymmetric thick domain wall solution with de Sitter (dS) expansion in five dimensions can be constructed from a symmetric one by using a same scalar (kink) with different potentials. In this paper, by presenting the mass-independent potentials of Kaluza-Klein (KK) modes in the corresponding Schrodinger equations, we investigate the localization and mass spectra of various bulk matter fields on the symmetric and asymmetric dS thick branes. For spin 0 scalars and spin 1 vectors, the potentials of KK modes in the corresponding Schrodinger equations are the modified Poschl-Teller potentials, and there exist a mass gap and a series of continuous spectrum. It is shown that the spectrum of scalar KK modes on the symmetric dS brane contains only one bound mode (the massless mode). However, for the asymmetric dS brane with a large asymmetric factor, there are two bound scalar KK modes: a zero mode and a massive mode. For spin 1 vectors, the spectra of KK modes on both dS branes consist of a bound massless mode and a set of continuous ones, i.e., the asymmetric factor does not change the number of the bound vector KK modes. For spin 1/2 fermions, two types of kink-fermion couplings are investigated in detail. For the usual Yukawa coupling ηΨ, there exists no mass gap but a continuous gapless spectrum of KK states. For the scalar-fermion coupling ηsin(/0)cos−δ(/0)Ψ with a positive coupling constant η, there exist some discrete bound KK modes and a series of continuous ones. The total number of bound states increases with the coupling constant η. For the case of the symmetric dS brane and positive η, there are NL(NL ≥ 1) left chiral fermion bound states (including zero mode and massive KK modes) and NL−1 right chiral fermion bound states (including only massive KK modes). For the asymmetric dS brane scenario, the asymmetric factor a reduces the number of the bound fermion KK modes. For large enough a, there would not be any right chiral fermion bound mode, but at least one left chiral fermion zero mode.

Entropy/Area spectra of the charged black hole from quasinormal modes

With the new physical interpretation of quasinormal modes proposed by Maggiore, the quantum area spectra of black holes have been investigated recently. Adopting the modified Hods treatment, results show that the area spectra for black holes are equally spaced and the spacings are in a unified form,

Hidden conformal symmetry of the Kerr-Newman black hole

△A=8\ensuremath{\pi}\ensuremath{\hbar}

Bulk matter fields on a GRS-inspired braneworld

, in Einstein gravity. On the other hand, following Kunstatters method, the studies show that the area spectrum for a nonrotating black hole with no charge is equidistant. And for a rotating (or charged) black hole, it is also equidistant and independent of the angular momentum

Particle collisions on stringy black hole background

J

Fermion Resonances on Multi-field Thick Branes

(or charge

Quantization of black hole entropy from quasinormal modes

q