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High Quality QCD Axion in the Standard Model

Jie Sheng, Tsutomu T. Yanagida

TL;DR

The paper demonstrates that anomaly-free discrete gauge symmetries $\mathbb{Z}_4 \times \mathbb{Z}_3$ embedded in the SM naturally produce a high-quality QCD axion via a Peccei–Quinn symmetry $U(1)_{PQ}$. It shows that the same setup yields two Higgs doublets, heavy Majorana neutrinos for the seesaw mechanism and leptogenesis, and a stable light fermion $\chi$ as a two-component dark matter scenario. A gravity-induced operator with $\Phi^{12}$ fixes the quality of the axion, sets the domain-wall number to $N_D=12$, and yields a predicted axion mass range $m_a \in [3\times 10^{-5}, 5\times 10^{-4}]$ eV with a decay constant $F_a \in [10^{11}, 2\times 10^{12}]$ GeV. The model makes testable predictions for upcoming haloscope searches and suggests subtle astrophysical effects from the light DM component, linking neutrino physics, baryogenesis, and DM within a minimal, SM-embedded framework.

Abstract

Although the axion is the most compelling solution to the strong CP problem, the ad hoc introduced global Peccei-Quinn symmetry suffers from a severe fine-tuning problem known as the quality problem. In this Letter, we show that the discrete gauge symmetry $\mathbb Z_4 \times \mathbb Z_3$ motivated from the internal structure of the Standard Model can naturally predict a high-quality axion, leading to a distinct and testable parameter space. Remarkably, this minimal framework simultaneously accounts for neutrino masses, baryon asymmetry, and dark matter.

High Quality QCD Axion in the Standard Model

TL;DR

The paper demonstrates that anomaly-free discrete gauge symmetries embedded in the SM naturally produce a high-quality QCD axion via a Peccei–Quinn symmetry . It shows that the same setup yields two Higgs doublets, heavy Majorana neutrinos for the seesaw mechanism and leptogenesis, and a stable light fermion as a two-component dark matter scenario. A gravity-induced operator with fixes the quality of the axion, sets the domain-wall number to , and yields a predicted axion mass range eV with a decay constant GeV. The model makes testable predictions for upcoming haloscope searches and suggests subtle astrophysical effects from the light DM component, linking neutrino physics, baryogenesis, and DM within a minimal, SM-embedded framework.

Abstract

Although the axion is the most compelling solution to the strong CP problem, the ad hoc introduced global Peccei-Quinn symmetry suffers from a severe fine-tuning problem known as the quality problem. In this Letter, we show that the discrete gauge symmetry motivated from the internal structure of the Standard Model can naturally predict a high-quality axion, leading to a distinct and testable parameter space. Remarkably, this minimal framework simultaneously accounts for neutrino masses, baryon asymmetry, and dark matter.
Paper Structure (5 sections, 14 equations, 1 figure, 2 tables)

This paper contains 5 sections, 14 equations, 1 figure, 2 tables.

Table of Contents

  1. Introduction
  2. Anomaly-Free Discrete Gauge Symmetries
  3. High-Quality Axion
  4. Two-Component Dark Matter
  5. Conclusion and Discussions

Figures (1)

  • Figure 1: Predicted parameter space of axion mass $m_a$ and coupling $g_{a\gamma \gamma}$ (Red solid line), and the Current haloscope experimental limits (Grey shaded region). The red dashed line shows the lower limit of axion mass with high quality. The benchmark KSVZ and DFSZ models are shown as blue dashed and solid lines, respectively. The future haloscope experimental projections are shown as gray dashed curves. All experimental limits are compiled from AxionLimits. Some of the astrophysical constraints in this mass range are not shown, as they are far from the predicted parameter space.