Fermion Masses and Mixing in General Warped Extra Dimensional Models

TL;DR

This paper explores how a universal flavor symmetry in a warped extra-dimensional model with bulk-propagating SM fields can naturally generate the observed fermion mass hierarchies and mixing patterns, including neutrinos.

Contribution

It introduces a generalized warped extra-dimensional framework with a universal flavor symmetry, linking fermion masses and mixings to the structure of 5D Yukawa couplings and wave-function sensitivities.

Findings

Hierarchical quark and charged lepton masses arise from wave-function sensitivities.

Neutrino masses and mixings are linked to flavor-symmetric 5D Yukawa couplings.

Model predictions are testable with future neutrino data.

Abstract

We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave-functions to small flavor breaking effects yield naturally hierarchical masses and mixing as it is usual in warped models with fermions in the bulk. In the neutrino sector, the exponential wave-function factors can be flavor-blind and thus insensitive to the small flavor symmetry breaking effects, directly linking their masses and mixing angles to the flavor symmetric structure of the 5D neutrino Yukawa couplings. The Higgs must be localized in the bulk and the model is naturally more successful in generalized warped scenarios where the metric background solution is different than $AdS_5$. We study these features in two simple frameworks, flavor complimentarily, and flavor democracy, which provide specific predictions and correlations between quarks and leptons, testable as more precise data in the neutrino sector becomes available.