Implications of Protecting the QCD Axion in the Dual Description

TL;DR

This paper explores the dual description of the QCD axion as a massive 2-form field, addressing the axion quality problem and its implications for axion phenomenology, cosmology, and potential signals like cosmic birefringence.

Contribution

It generalizes the dual description of the QCD axion to include multiple 3-forms, proposing a solution to the axion quality problem and exploring its phenomenological consequences.

Findings

Multiple 3-forms can resolve the axion quality problem.

Enhanced axion-photon coupling suggests new search avenues.

Large decay constant QCD axion remains cosmologically viable.

Abstract

The QCD axion can be be formulated in a dual description as a massive 2-form field. In this picture, the QCD axion quality problem translates into the question if there are additional 3-forms coupled to the axion other than the QCD 3-form that emerges at low energy. If such forms exist, the quality problem can be resolved via the introduction of other massive 2-forms (and thus corresponding axions), one for each additional 3-form. This can motivate an "axiverse from a high quality QCD axion". In this work, we discuss this issue in the general case where the QCD axion couples to arbitrarily many 3-forms. Given the multiple axion solution, we discuss the phenomenological implications of the enhanced quality of the QCD axion in the dual description. These include sub-eV axion-like particle search through the axion-photon coupling, the cosmological consistency of a large decay constant QCD axion, and a model for the observed cosmic birefringence.