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Fermion Masses, Mixings and Proton Decay in a Randall-Sundrum Model

Stephan J. Huber, Qaisar Shafi

TL;DR

This work embeds the Standard Model in a warped Randall-Sundrum background with bulk fermions and gauge fields to explain the observed fermion mass spectrum without hierarchical Yukawa couplings. Fermion localization along the extra dimension, controlled by the bulk mass parameter $c$, yields overlapping profiles with a TeV-brane Higgs that reproduce charged-lepton and quark masses and CKM mixings, while placing KK states around $\mathcal{O}(10\,\text{TeV})$. Dimension-six proton-decay operators experience partial suppression from fermion localization, but the resulting scales $M_4$ fall short of experimental bounds unless the dimensionless couplings are as small as $\mathcal{O}(10^{-8})$, indicating a need for further suppression or symmetry. Dimension-five neutrino masses pose a challenge in the minimal setup, giving masses far above or below the observed scales depending on assumptions, and atmospheric/neutrino-oscillation data appear incompatible without extending the model, e.g., by introducing right-handed neutrinos or additional symmetries.

Abstract

We consider a Randall-Sundrum model in which the Standard Model fermions and gauge bosons correspond to bulk fields. We show how the observed charged fermion masses and CKM mixings can be explained, without introducing hierarchical Yukawa couplings. We then study the impact on the mass scales associated with non-renormalizable operators responsible for proton decay, neutrino masses, and flavor changing neutral currents. Although mass scales as high as 10^{11}- 10^{12} GeV are in principle possible, dimensionless couplings of order 10^{-8} are still needed to adequately suppress proton decay. Large neutrino mixings seem to require new physics beyond the Standard Model.

Fermion Masses, Mixings and Proton Decay in a Randall-Sundrum Model

TL;DR

This work embeds the Standard Model in a warped Randall-Sundrum background with bulk fermions and gauge fields to explain the observed fermion mass spectrum without hierarchical Yukawa couplings. Fermion localization along the extra dimension, controlled by the bulk mass parameter , yields overlapping profiles with a TeV-brane Higgs that reproduce charged-lepton and quark masses and CKM mixings, while placing KK states around . Dimension-six proton-decay operators experience partial suppression from fermion localization, but the resulting scales fall short of experimental bounds unless the dimensionless couplings are as small as , indicating a need for further suppression or symmetry. Dimension-five neutrino masses pose a challenge in the minimal setup, giving masses far above or below the observed scales depending on assumptions, and atmospheric/neutrino-oscillation data appear incompatible without extending the model, e.g., by introducing right-handed neutrinos or additional symmetries.

Abstract

We consider a Randall-Sundrum model in which the Standard Model fermions and gauge bosons correspond to bulk fields. We show how the observed charged fermion masses and CKM mixings can be explained, without introducing hierarchical Yukawa couplings. We then study the impact on the mass scales associated with non-renormalizable operators responsible for proton decay, neutrino masses, and flavor changing neutral currents. Although mass scales as high as 10^{11}- 10^{12} GeV are in principle possible, dimensionless couplings of order 10^{-8} are still needed to adequately suppress proton decay. Large neutrino mixings seem to require new physics beyond the Standard Model.

Paper Structure

This paper contains 5 sections, 22 equations, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. 5d fermions
  3. Masses for bulk quarks and leptons
  4. Dimension six operators and proton decay
  5. Dimension five neutrino masses

Figures (1)

  • Figure 1: Localization of the electron ($c=0.681$), tau ($c=0.537$) and right-handed top quark ($c=0.1$) zero modes in the fifth dimension. The Higgs profile $H$ is given for $a=4$ in units of $k^{3/2}$ and magnified by a factor of 10.