Revisiting Electroweak Phase Transition with Varying Yukawa Coupling Constants

TL;DR

This paper examines how large Yukawa couplings influence the electroweak phase transition and Higgs potential stability, revealing that such couplings can destabilize the potential at low scales and alter Higgs mass predictions.

Contribution

It demonstrates that large Yukawa couplings significantly impact the Higgs potential stability and the strength of the electroweak phase transition, challenging previous assumptions in electroweak baryogenesis models.

Findings

Yukawa couplings beyond the top quark lower the instability scale of the Higgs potential.

Adding order one Yukawa couplings causes the potential to become unstable at the TeV scale.

The scenario predicts a lighter Higgs mass than observed, weakening the phase transition.

Abstract

We revisited the scenario of electroweak baryogenesis in the presence of large Yukawa couplings, in which it was found previously that a strongly first order electroweak phase transition can occur with the Higgs mass at its observed value of 125 GeV. Given the sensitivity of the running of the Higgs quartic coupling on the Yukawa coupling constants, we find that the addition of order one Yukawa couplings beyond the top quark drastically lowers the scale at which the Higgs potential becomes unstable. Specifically, even with only one additional order one Yukawa coupling, the scalar potential becomes unstable already at the TeV scale, assuming the Standard Model values for the Higgs sector parameters at the electroweak scale. Furthermore, by assuming the Standard Model values for the Higgs sector parameters at the TeV scale, the quartic coupling constant is driven to be larger than its Standard Model value at the electroweak scale. This in turn predicts a much lighter Higgs mass than the measured value of 125 GeV. In this scenario, the strength of the electroweak phase transition is also significantly weakened.