Cosmological evolution of Yukawa couplings: the 5D perspective

TL;DR

This paper explores how the evolution of Yukawa couplings in a 5D Randall-Sundrum model can lead to significant CP-violation during the electroweak phase transition, with implications for baryogenesis.

Contribution

It provides a natural realization of Yukawa coupling variation in Randall-Sundrum models via the Goldberger-Wise scalar, linking flavor dynamics to cosmological CP-violation.

Findings

Yukawa couplings can vary during the stabilization of the Randall-Sundrum geometry.

This variation can induce large CP-violation during electroweak baryogenesis.

The model alleviates constraints from CP-violation in extra-dimensional scenarios.

Abstract

The cosmological evolution of standard model Yukawa couplings may have major implications for baryogenesis. In particular, as highlighted recently, the CKM matrix alone could be the source of CP-violation during electroweak baryogenesis provided that the Yukawa couplings were large and varied during the electroweak phase transition. We provide a natural realisation of this idea in the context of Randall-Sundrum models and show that the geometrical warped approach to the fermion mass hierarchy may naturally display the desired cosmological dynamics. The key ingredient is the coupling of the Goldberger-Wise scalar, responsible for the IR brane stabilisation, to the bulk fermions, which modifies the fermionic profiles. This also helps alleviating the usually tight constraints from CP-violation in Randall-Sundrum scenarios. We study how the Yukawa couplings vary during the stabilisation of the Randall-Sundrum geometry and can thus induce large CP-violation during the electroweak phase transition. Using holography, we discuss the 4D interpretation of this dynamical interplay between flavour and electroweak symmetry breaking.