Zhen-Hua Zhao

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.

Fermion Resonances on Multi-field Thick Branes

Motivated by the recent work on the fermion resonances on scalar-constructed thick branes (arXiv:0901.3543 and arXiv:0904.1785), we extend the idea to multi-scalar generated thick branes and complete previous work. The fermion localization and reso- nances on the three-field and two-field thick branes are investigated. With the Numerov method, our numerical results show that the resonance states also exist in the brane be- sides the single-field thick branes and the two-field thick branes in the former cases. This interesting phenomenon is related to the internal structure of the brane and the coupling of fermions and scalars. We find that the Kaluza-Klein chiral decomposition of massive fermion resonances is the parity-chiral decomposition. For the couplings ��� k ��� and ��� k �� for three-field and two-field models with odd positive k, respectively, the number of the resonant states decreases with k. This result is opposite to the one obtained in the single-field de Sitter thick brane (arXiv:0904.1785).

Domain wall brane in squared curvature gravity

We suggest a thick braneworld model in the squared curvature gravity theory. Despite the appearance of higher order derivatives, the localization of gravity and various bulk matter fields is shown to be possible. The existence of the normalizable gravitational zero mode indicates that our four-dimensional gravity is reproduced. In order to localize the chiral fermions on the brane, two types of coupling between the fermions and the brane forming scalar is introduced. The first coupling leads us to a Schrödinger equation with a volcano potential, and the other a Pöschl-Teller potential. In both cases, the zero mode exists only for the left-hand fermions. Several massive KK states of the fermions can be trapped on the brane, either as resonant states or as bound states.

Fermion localization on asymmetric two-field thick branes

In this paper we investigate the localization of fermions on asymmetric thick branes generated by two scalars and χ. In order to trap fermions on the asymmetric branes with kink-like warp factors, the couplings with the background scalars are introduced, where F(χ, ) is a function of and χ. We find that the coupling does not support the localization of four-dimensional fermions on the branes. While, for the case , which is the kink-fermion coupling corresponding to one-scalar-generated brane scenarios, the zero mode of left-handed fermions could be trapped on the branes under some conditions.

Fermion Resonances on a Thick Brane with a Piecewise Warp Factor

In this paper, we mainly investigate the problems of resonances of massive KK fermions on a single scalar constructed thick brane with a piecewise warp factor matching smoothly. The distance between two boundaries and the other parameters are determined by one free parameter through three junction conditions. For the generalized Yukawa coupling

Effects of temperature on thick branes and the fermion (quasi-)localization

\eta\bar{\Psi}\phi^{k}\Psi

Non-perturbative procedure for stable K-brane

with odd

Holographic Josephson Junction in 3+1 dimensions

k=1,3,5,...

Fermions on Asymmetric Bloch Branes

, the mass eigenvalue

Fermion Resonances on a Finite Thickness Brane

m