Peccei-Quinn Relaxion

TL;DR

This paper proposes a novel scenario where the QCD anomaly-induced potential simultaneously addresses the electroweak hierarchy problem and the strong CP problem, extending the cutoff scale and accommodating dark matter within cosmological constraints.

Contribution

It introduces a new relaxion-QCD axion model with inflaton-dependent potentials, raising the Higgs cutoff scale to 10^7 GeV and enabling higher reheating temperatures.

Findings

Raises Higgs mass cutoff to 10^7 GeV

Allows reheating temperature above electroweak scale

QCD axion accounts for dark matter

Abstract

The relaxation mechanism, which solves the electroweak hierarchy problem without relying on TeV scale new physics, crucially depends on how a Higgs-dependent back-reaction potential is generated. In this paper, we suggest a new scenario in which the scalar potential induced by the QCD anomaly is responsible both for the relaxation mechanism and the Peccei-Quinn mechanism to solve the strong CP problem. The key idea is to introduce the relaxion and the QCD axion whose cosmic evolutions become quite different depending on an inflaton-dependent scalar potential. Our scheme raises the cutoff scale of the Higgs mass up to 10^7 GeV, and allows reheating temperature higher than the electroweak scale as would be required for viable cosmology. In addition, the QCD axion can account for the observed dark matter of the universe as produced by the conventional misalignment mechanism. We also consider the possibility that the couplings of the Standard Model depend on the inflaton and become stronger during inflation. In this case, the relaxation can be implemented with a sub-Planckian field excursion of the relaxion for a cutoff scale below 10 TeV.