Bulk Majorana mass terms and Dirac neutrinos in Randall Sundrum Model

TL;DR

This paper proposes a model within the Randall-Sundrum framework where neutrinos are primarily Dirac particles despite the presence of Majorana mass terms, and discusses the phenomenological implications and Higgs sector extensions.

Contribution

It introduces a novel scheme for realizing Dirac neutrinos with Majorana mass terms in Randall-Sundrum models, including a two-Higgs extension for realistic lepton mass fitting.

Findings

Massless zero mode solutions exist when bulk Dirac mass is zero.

Effective neutrino mass is mainly Dirac with negligible Majorana contributions.

Two-Higgs extension enables proper lepton mass fitting.

Abstract

We present a novel scheme where Dirac neutrinos are realized even if lepton number violating Majorana mass terms are present. The setup is the Randall-Sundrum framework with bulk right handed neutrinos. Bulk mass terms of both Majorana and Dirac type are considered. It is shown that massless zero mode solutions exist when the bulk Dirac mass term is set to zero. In this limit, it is found that the effective 4D small neutrino mass is primarily of Dirac nature with the Majorana type contributions being negligible. Interestingly, this scenario is very similar to the one known with flat extra dimensions. Neutrino phenomenology is discussed by fitting both charged lepton masses and neutrino masses simultaneously. A single Higgs localised on the IR brane is highly constrained as unnaturally large Yukawa couplings are required to fit charged lepton masses. A simple extension with two Higgs doublets is presented which facilitates a proper fit for the lepton masses.