Peccei-Quinn Symmetry Breaking via Asymptotically Safe Dynamical Scalegenesis: A Walking Axicolor and Axion

TL;DR

This paper proposes a novel asymptotically safe dynamical mechanism for Peccei-Quinn symmetry breaking that resolves hierarchy and triviality problems, leading to a naturally light composite axion consistent with QCD constraints.

Contribution

It introduces an asymptotically safe axicolor model with walking dynamics that dynamically breaks PQ symmetry and generates the axion scale without hierarchy or triviality issues.

Findings

The model achieves scale generation via nonperturbative dimensional transmutation.

The composite axion can be light and acts as the QCD axion in the anti-Veneziano limit.

The framework maintains quantum scale invariance during the walking regime.

Abstract

Pecci-Quinn (PQ) symmetry breaking by perturbative dynamics would suffer from a hierarchy problem, just like the electroweak symmetry breaking in the standard model. The dynamics of the axion, associated with the PQ symmetry breaking, would also involve a triviality problem. We provide a paradigm to resolve those two problems potentially existing in the PQ symmetry breaking scenario, with keeping successful axion relaxation for the QCD strong CP phase. The proposed theory includes an axicolor dynamics with the axicolored fermions partially gauged by the QCD color, and is shown to be governed by an asymptotically safe (AS) fixed point: quantum scale invariance is built. The AS axicolor is actually a ``walking" dynamics, which dynamically breaks a PQ symmetry, a part of the chiral symmetry carried by the axicolored fermions. The PQ scale generation is then triggered by the nonperturbative dimensional transmutation in the ``walking" dynamics. A composite axion emerges as the assosiated Nambu-Goldstone boson. That is, no hierarchy or triviality problem is present there. The composite axion can potentially be light due to the characteristic feature of the AS axicolor (``walking" axicolor), becomes the QCD axion in the anti-Veneziano limit, and gets heavier by the subleading correction. The composite axion relaxes the QCD theta parameter, involving heavier relaxation partners such as axicolored pseudoscalar mesons, and the ultraviolet correction to the relaxation mechanism is protected by the established (near) scale invariance during the ``walking" regime.