An ultra-weak sector, the strong CP problem and the pseudo-Goldstone dilaton

TL;DR

This paper proposes a model with ultra-weak couplings and a pseudo-Goldstone dilaton that addresses the strong CP problem, explains electroweak symmetry breaking, and provides a dark matter candidate, all while maintaining naturalness.

Contribution

It introduces a novel ultra-weak sector with a gauge-singlet scalar that solves the strong CP problem and generates electroweak symmetry breaking without hierarchy issues.

Findings

The model naturally incorporates an invisible axion as dark matter.

It predicts a light pseudo-Goldstone dilaton consistent with cosmological bounds.

A supersymmetric extension can avoid hierarchy problems in grand unification contexts.

Abstract

In the context of a Coleman-Weinberg mechanism for the Higgs boson mass, we address the strong CP problem. We show that a DFSZ-like invisible axion model with a gauge-singlet complex scalar field S, whose couplings to the Standard Model are naturally ultra-weak, can solve the strong CP problem and simultaneously generate acceptable electroweak symmetry breaking. The ultra-weak couplings of the singlet S are associated with underlying approximate shift symmetries that act as custodial symmetries and maintain technical naturalness. The model also contains a very light pseudo-Goldstone dilaton that is consistent with cosmological Polonyi bounds, and the axion can be the dark matter of the universe. We further outline how a SUSY version of this model, which may be required in the context of Grand Unification, can avoid introducing a hierarchy problem.