Fat brane and seesaw mechanism in extra dimensions

TL;DR

This paper proposes a higher-dimensional seesaw mechanism with a fat brane in extra dimensions, generating sterile neutrinos that explain small SM neutrino masses and allowing viable leptogenesis within certain parameter ranges.

Contribution

It introduces a novel higher-dimensional seesaw model with a fat brane, suppressing sterile neutrino interactions and enabling TeV-scale sterile neutrinos consistent with neutrino mass and leptogenesis.

Findings

Sterile neutrino masses can be of order 1-10 TeV.

Small SM neutrino masses are naturally explained.

Leptogenesis is viable for specific parameter choices.

Abstract

In this paper we present a higher-dimensional seesaw mechanism. We consider a single, flat extra dimension, where a fat brane is localized and contains the standard model (SM) fields, similar to Universal Extra Dimension models. There is only one Dirac fermion in the bulk, and in four dimensions it results in two towers of Kaluza-Klein (KK) Majorana sterile neutrinos, whose mass mixing with the SM neutrinos is suppressed due to a brane-localized kinetic term. The interaction between the sterile neutrinos and the SM is through the usual coupling with the Higgs boson, where the coupling depends upon the compactification radius $R^{-1}=10^{-2}-1$ GeV and the width of the fat brane $L^{-1}=2$ TeV, where the latter value is chosen to avoid LHC constraints. Due to this suppression mechanism the mass of the lightest sterile neutrinos can be of order $\mathcal{O}(1-10)$~\text{TeV} while naturally explaining the small SM neutrino mass, which in turn is easily obtained for a large range of parameter choices. Furthermore, neutrino oscillations are not substantially influenced by the tower of sterile KK particles. Finally, leptogenesis is investigated in this setup, and it is viable for some values within the parameter space.