Small Instanton Effects on Composite Axion Mass

Kavli Affiliate: Satoshi Shirai

| First 5 Authors: Takafumi Aoki, Masahiro Ibe, Satoshi Shirai, Keiichi Watanabe,

| Summary:

This paper investigates the impact of small instanton effects on the axion
mass in the composite accidental axion (CAA) models. These models are designed
to address the axion quality problem, where QCD gauge symmetry is embedded as
an unbroken diagonal subgroup of a product gauge group. These models contain
small instantons not included in low-energy QCD, which could enhance the axion
mass significantly. However, in the CAA models, our analysis reveals that these
effects on the axion mass are non-vanishing but are negligible compared to the
QCD effects. This highlights the important role of anomalous but
non-spontaneously broken U(1) symmetries in restricting the impact of small
instantons on the axion mass. Our study provides crucial insights into the
dynamics within CAA models and suggests broader implications for understanding
small instanton effects in other composite axion models.

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