Dynamics of the cosmological relaxation after reheating

TL;DR

This paper investigates whether the cosmological relaxation mechanism for the hierarchy problem remains viable at high reheating temperatures, proposing dark gauge boson coupling as a solution to stabilize the relaxion.

Contribution

It introduces a dark gauge boson coupling to provide friction that stabilizes the relaxion after reheating, extending the relaxation mechanism's viability at high temperatures.

Findings

Dark gauge boson coupling effectively slows relaxion at high temperatures.

Relaxion can be stabilized after electroweak transition with dark gauge interactions.

The mechanism remains consistent with observational constraints.

Abstract

We examine if the cosmological relaxation mechanism, which was proposed recently as a new solution to the hierarchy problem, can be compatible with high reheating temperature well above the weak scale. As the barrier potential disappears at high temperature, the relaxion rolls down further after the reheating, which may ruin the successful implementation of the relaxation mechanism. It is noted that if the relaxion is coupled to a dark gauge boson, the new frictional force arising from dark gauge boson production can efficiently slow down the relaxion motion, which allows the relaxion to be stabilized after the electroweak phase transition for a wide range of model parameters, while satisfying the known observational constraints.