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Testable Inverse Seesaw Motivated from a High Quality QCD Axion

Yannis Georis, Jie Sheng, Salvador Urrea, Tsutomu T. Yanagida

TL;DR

The paper addresses the dual challenges of explaining tiny neutrino masses and solving the strong CP problem by linking them through a minimal framework based on gauging the discrete symmetry $\mathbb{Z}_4 \times \mathbb{Z}_3$. This symmetry naturally yields a high-quality QCD axion and enforces the field content needed for an inverse seesaw (ISS) with three pairs of heavy states, arising from Planck-suppressed operators involving the PQ field. The resulting setup predicts three pseudo-Dirac heavy neutrino pairs with GeV-scale masses and sizable active–sterile mixing, testable in SHiP, HL-LHC, FCC-ee, and CEPC, while correlating neutrino masses with axion quality and providing a dark-matter candidate and leptogenesis avenues. The model yields a well-motivated, highly predictive framework connecting strong CP, neutrino physics, dark matter, and baryogenesis, with concrete experimental prospections in the near future. Overall, it offers a cohesive path to test beyond-Standard-Model physics that simultaneously addresses multiple open questions in particle physics and cosmology.

Abstract

The QCD axion remains one of the most compelling solutions to the strong CP problem. Meanwhile, the type-I seesaw mechanism offers an elegant explanation for the lightness of the observed neutrino masses; however, its extremely heavy Majorana states place it far beyond experimental reach. Low-scale alternatives such as the inverse seesaw improve testability but typically lack a strong theoretical motivation. In this paper we bridge this gap by showing that gauging the discrete symmetry $\mathbb Z_4 \times \mathbb Z_3$-motivated by the internal structure of the Standard Model-naturally yields a QCD axion with a high-quality Peccei-Quinn symmetry solving the strong CP problem, while simultaneously enforcing the field content and hierarchy required for a natural inverse seesaw. The resulting model is highly predictive and has the potential to be fully tested by future experiments. Beyond addressing the strong CP problem and the origin of neutrino masses, our scenario also contains a viable dark-matter candidate and offers potential mechanisms for generating the baryon asymmetry of the Universe.

Testable Inverse Seesaw Motivated from a High Quality QCD Axion

TL;DR

The paper addresses the dual challenges of explaining tiny neutrino masses and solving the strong CP problem by linking them through a minimal framework based on gauging the discrete symmetry . This symmetry naturally yields a high-quality QCD axion and enforces the field content needed for an inverse seesaw (ISS) with three pairs of heavy states, arising from Planck-suppressed operators involving the PQ field. The resulting setup predicts three pseudo-Dirac heavy neutrino pairs with GeV-scale masses and sizable active–sterile mixing, testable in SHiP, HL-LHC, FCC-ee, and CEPC, while correlating neutrino masses with axion quality and providing a dark-matter candidate and leptogenesis avenues. The model yields a well-motivated, highly predictive framework connecting strong CP, neutrino physics, dark matter, and baryogenesis, with concrete experimental prospections in the near future. Overall, it offers a cohesive path to test beyond-Standard-Model physics that simultaneously addresses multiple open questions in particle physics and cosmology.

Abstract

The QCD axion remains one of the most compelling solutions to the strong CP problem. Meanwhile, the type-I seesaw mechanism offers an elegant explanation for the lightness of the observed neutrino masses; however, its extremely heavy Majorana states place it far beyond experimental reach. Low-scale alternatives such as the inverse seesaw improve testability but typically lack a strong theoretical motivation. In this paper we bridge this gap by showing that gauging the discrete symmetry -motivated by the internal structure of the Standard Model-naturally yields a QCD axion with a high-quality Peccei-Quinn symmetry solving the strong CP problem, while simultaneously enforcing the field content and hierarchy required for a natural inverse seesaw. The resulting model is highly predictive and has the potential to be fully tested by future experiments. Beyond addressing the strong CP problem and the origin of neutrino masses, our scenario also contains a viable dark-matter candidate and offers potential mechanisms for generating the baryon asymmetry of the Universe.

Paper Structure

This paper contains 6 sections, 16 equations, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Brief review on the high quality QCD axion in the Standard Model
  3. Neutrino Mass generation From Inverse Seesaw
  4. Experimental Constraints and Future Projections
  5. Conclusion and Discussions
  6. acknowledgments

Figures (1)

  • Figure 1: Points consistent with neutrino oscillation data and allowed by our model. Red (blue) points correspond to normal (inverted) mass ordering. The gray shaded regions denote current experimental constraints Fernandez-Martinez:2023phj, and the brown shaded area is disfavored by BBN bounds extracted from Abdullahi:2022jlvBoyarsky:2020dzc. The dashed lines indicate the projected sensitivities of the SHiP experiment Aberle:2839677Antel:2023hkf, the HL-LHC (CMS displaced-vertex searches) Izaguirre:2015pgaDrewes:2019fou and FCC-ee/CEPC Blondel:2022qqoCEPCStudyGroup:2018ghiAi:2025cpj. These sensitivity lines have been derived in a simplified framework assuming a unique heavy neutrino $N$ solely coupled to the SM flavor $\alpha$.