Lepton Masses and Flavor Violation in Randall Sundrum Model

TL;DR

This paper investigates lepton masses, mixing, and flavor violation in Randall-Sundrum models with different neutrino mass mechanisms, analyzing constraints and fitting data with various bulk mass parameters and Yukawa couplings.

Contribution

It provides a detailed analysis of lepton flavor physics in Randall-Sundrum models considering three neutrino mass scenarios, including numerical solutions and flavor violation constraints.

Findings

Large negative bulk mass parameters needed for right-handed fields in LH LH case

Good fits for bulk mass parameters between 0 and 1 in Dirac case

Lepton flavor violating rates are large for certain neutrino hierarchy points

Abstract

Lepton masses and mixing angles via localization of 5D fields in the bulk are revisited in the context of Randall-Sundrum models. The Higgs is assumed to be localized on the IR brane. Three cases for neutrino masses are considered: (a) The higher dimensional LH.LH operator (b) Dirac masses (c) Type I see-saw with bulk Majorana mass terms. Neutrino masses and mixing as well as charged lepton masses are fit in the first two cases using $\chi^2$ minimisation for the bulk mass parameters, while varying the $\mathcal{O}(1)$ Yukawa couplings between 0.1 and 4. Lepton flavour violation is studied for all the three cases. It is shown that large negative bulk mass parameters are required for the right handed fields to fit the data in the LH LH case. This case is characterized by a very large Kaluza-Klein (KK) spectrum and relatively weak flavour violating constraints at leading order. The zero modes for the charged singlets are composite in this case and their corresponding effective 4-D Yukawa couplings to the KK modes could be large. For the Dirac case, good fits can be obtained for the bulk mass parameters, $c_i$, lying between 0 and 1. However, most of the `best fit regions' are ruled out from flavour violating constraints. In the bulk Majorana terms case, we have solved the profile equations numerically. We give example points for inverted hierarchy and normal hierarchy of neutrino masses. Lepton flavor violating rates are large for these points. We then discuss various minimal flavor violation (MFV) schemes for Dirac and bulk Majorana cases. In the Dirac case with MFV hypothesis, it is possible to simultaneously fit leptonic masses and mixing angles and alleviate lepton flavor violating constraints for Kaluza-Klein modes with masses of around 3 TeV. Similar examples are also provided in the Majorana case.