The Fermion Resonances On Thick Brane

In this thesis, we focus on the fermion localization and quasi-localization (resonances) on two topologically non-trivial thick branes.Firstly, we give an overview of extra-dimensional physics and the braneworld theories. Three different pictures of an extra dimension are reviewed, namely, Kaluza-Klein(KK) theory, ADD model and RS model. We then move on to the construction of thick brane and compare it with the thin brane.Secondly, we study the fermion resonances on multi-scalar generated thick branes. Specifically, the fermion localization and resonances on the three-field thick brane are investigated. Our numerical results show that the resonant states also exist on the brane as that on the single-field thick branes and the two-field thick branes. It is found that the Kaluza-Klein chiral decomposition of massive fermion resonances is the parity-chiral decomposition. For a generalized Yukawa coupling with a power function of the bulk scalar field with an odd exponent, the number of the resonant states decreases with the power exponent. This result is opposite to the one obtained in the single-field de Sitter thick brane.Finally, we construct a thick brane with a piecewise warp factor matching smoothly and investigate the problem of resonances of massive KK fermions on the thick brane. The distance between two boundaries and the other parameters are determined by one free parameter through three junction conditions. For the generalized Yukawa coupling, it is found that the brane without internal structure also favors the appearance of resonant states for both left-and right-handed fermions. The scalar-fermion coupling and the thickness of the brane influence the resonant behaviors of the massive KK fermions.