Axion identification in multi-phase models

@misc{lei2026axion,
  title = {{Axion identification in multi-phase models}},
  author = {Zhen-Yu Lei and Jian-Wei Cui},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.24028},
  eprint = {2610.24028},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.24028},
}

TY  - UNPB
TI  - Axion identification in multi-phase models
AU  - Zhen-Yu Lei
AU  - Jian-Wei Cui
PY  - 2026
DA  - 2026/10/16
PB  - arXiv
DO  - 10.48550/arxiv.2610.24028
UR  - https://arxiv.org/abs/2610.24028
AB  - Axion identification in multi-phase models is subtle because local mass eigenstates do not by themselves determine global properties such as the fundamental period and domain-wall number. In this paper, we develop a route to identify the axion in a broad class of multi-phase models, including DFSZ-like theories. The construction involves two reductions: gauge identification and integrating out heavy phase fields. We study these reductions explicitly in two representative two-phase models. Gauge identification reduces the compact field space of the phase fields to a quotient space by identifying points connected by gauge transformations, while integrating out heavy phase fields restricts the low-energy dynamics to nonlinear orbits. Under the stated assumptions and within the validity of the derivative expansion, the physical low-energy field space forms a finite union of S^1. The axion is identified as the effective field on an S^1 orbit and coincides locally with the lightest mass eigenstate near the vacuum. Its fundamental period and domain-wall number are well-defined and can be determined from the original Lagrangian. Nevertheless, the reduction to a single axion does not capture all properties of topological defects in the original multi-phase theory. In particular, axion strings can retain nontrivial gauge flux, while special defect configurations can involve non-negligible spacetime derivatives of the heavy phase fields and invalidate the single-field reduction. These effects represent fundamental differences between multi-phase and single-phase theories at the level of topological defects.
ER  -