Hybrid SO(10) Axion Model Without Quality Problem

TL;DR

This paper introduces a hybrid SO(10) axion model that naturally solves the quality problem without fine-tuning, predicts unique axion couplings, and offers a comprehensive framework for fermion masses, dark matter, and cosmological issues.

Contribution

It presents a new SO(10)×U(1)_a gauge model where the PQ symmetry is accidental, avoiding quantum gravity violations and unifying features of KSVZ and DFSZ axion models.

Findings

PQ breaking scale up to 4×10^{11} GeV compatible with dark matter

Distinct axion-nucleon and axion-electron coupling predictions

No domain wall problem and realistic fermion mass framework

Abstract

Invisible axion models that solve the strong CP problem via the Peccei-Quinn (PQ) mechanism typically have a quality problem that arises from quantum gravity effects which violate all global symmetries. These models therefore require extreme fine-tuning of parameters for consistency. We present a new solution to the quality problem in a unified $SO(10)\times U(1)_a$ gauge model, where $U(1)_a$ is an anomaly free axial gauge symmetry. PQ symmetry emerges as an accidental symmetry in this setup, which admits a PQ breaking scale as large as $4\times 10^{11}$ GeV, allowing for the axion to be the cosmological dark matter. We call this a hybrid axion model due to its unique feature that it interpolates between the popular KSVZ and DFSZ axion models. Its predictions for the experimentally measurable axion couplings to the nucleon and electron are distinct from those of the usual models, a feature that can be used to test it. Furthermore, the model has no domain wall problem and it provides a realistic and predictive framework for fermion masses and mixings.