It has been shown that certain W algebras can be linearized by the inclusion of a spin-1 current. This Provides a way of obtaining new realizations of the W algebras. In this paper, we investigate the new ghost field realizations of the W2,s(s = 3, 4) algebras, making use of the fact that these two algebras can be linearized. We then construct the nilpotent BRST charges of the spinor non-critical W2,s strings with these new realizations.

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 Schröodinger 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 P¨oschl-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, there exists no mass gap but a continuous gapless spectrum of KK states. For the scalar-fermion couplingsin(0) cos−(0) with a positive coupling constant, there exist some discrete bound KK modes and a series of continuous ones. The total number of bound states increases with the coupling constant. For the case of the symmetric dS brane and positive, there are NL(NL1) 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.

A three-parameter (positive odd integers, thickness factor, and asymmetry factora) family of asymmetric thick brane solutions in five dimensions were constructed from a two-parameter (s and) family of symmetric ones in [R. Guerrero, R.O. Rodriguez, and R. Torrealba, Phys. Rev. D72, 124012 (2005).]. The values s = 1 and s 3 correspond to single branes and double branes,respectively. These branes have very rich inner structure. In this paper, by presenting the massindependent potentials of Kaluza–Klein (KK) modes in the corresponding Schrodinger equations,we investigate the localization and mass spectra of fermions on the symmetric and asymmetric thick branes in an AdS background. In order to analyze the effect of gravity-fermion interaction (i.e., the effect of the inner structure of the branes) and scalar-fermion interaction to the spectrum of fermion KK modes, we consider three kinds of typical kink-fermion couplings. The spectra of left chiral fermions for these couplings are consisted of a bound zero mode and a series of gapless continuous massive KK modes, some discrete bound KK modes including zero mode (exist mass gaps) and a series of continuous massive KK modes, infinite discrete bound KK modes, respectively. The structures of the spectra are investigated in detail.

In this paper, we mainly investigate the WM2,s WL2,s system, in which the matter and the Liouville subsystems generate WM2,s and WL2,s algebras respectively. We first give a brief discussion of the physical states for corresponding W stings. The lower states are given by freezing the spin-2 and spin-s currents.Then, introducing two pairs of ghost-like fields, we give the realizations of W1,2,s algebras. Based on these linear realizations, BRST operators for W2,s algebras are obtained. Finally, we construct new BRST charges of Liouville system for WL2,s strings at the specific values of central charges c: c = −225/5 for WL2,3 algebra,c = −24 for WL2,4 algebra and c = −2,−286 /3 for WL2,6 algebra, at which the corresponding WL 2,s algebras are singular.

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 resonances 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 besides 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).