Scalar kinks and fermion localisation in warped spacetimes

TL;DR

This paper explores how scalar kinks in warped spacetimes can localize massive fermions on a brane, analyzing the spectrum and lifetimes of quasi-bound states with different Yukawa couplings.

Contribution

It provides exact solutions of Einstein-scalar equations with a sine-Gordon potential and studies fermion localization and quasi-bound states in this setup.

Findings

Massive fermions can be localized with tunable parameters.

Lifetimes of quasi-bound states increase exponentially with coupling.

Finite probability of fermion escape into the bulk.

Abstract

Scalar kinks propagating along the bulk in warped spacetimes provide a thick brane realisation of the braneworld. We consider here, a class of such exact solutions of the full Einstein-scalar system with a sine-Gordon potential and a negative cosmological constant. In the background of the kink and the corresponding warped geometry, we discuss the issue of localisation of spin half fermions (with emphasis on massive ones) on the brane in the presence of different types of kink-fermion Yukawa couplings. We analyse the possibility of quasi-bound states for large values of the Yukawa coupling parameter $\gamma_F$ (with $\nu$, the warp factor parameter kept fixed) using appropriate, recently developed, approximation methods. In particular, the spectrum of the low--lying states and their lifetimes are obtained, with the latter being exponentially enhanced for large $\nu \gamma_F$. Our results indicate quantitatively, within this model, that it is possible to tune the nature of warping and the strength and form of the Yukawa interaction to obtain trapped massive fermion states on the brane, which, however, do have a finite (but very small) probability of escaping into the bulk.