Fermion Mass Hierarchy from the Soft Wall

TL;DR

This paper presents a 5D soft wall model where fermion mass hierarchies emerge from a power-law relationship between fermion masses and Yukawa couplings, without requiring hierarchical bulk masses.

Contribution

It introduces a novel 5D soft wall framework that reproduces the Standard Model fermion mass hierarchy through non-universal fermionic bulk masses.

Findings

Fermion masses follow a power-law dependence on Yukawa couplings.

The model reproduces the full range of SM fermion masses.

Non-hierarchical bulk masses can generate observed mass hierarchies.

Abstract

We develop a 5d model for ElectroWeak physics based on a non compact warped extra dimension of finite length, known as the soft wall scenario, where all the dynamical degrees of freedom propagate in the 5d bulk. We solve the equations of motion and find the allowed spectra, showing that the mass of the lightest fermionic mode behaves as a power law of the effective 4d Yukawa coupling constant, with the exponent being the corresponding fermionic 5d bulk mass. Precisely this non universal behavior allows us to reproduce the hierarchy between the Standard Model (SM) fermion masses (from neutrinos to the top quark) with non-hierarchical fermionic bulk masses.