Speaker
Description
Peccei-Quinn (PQ) mechanism is a prominent solution to the strong CP problem. In this mechanism, spontaneous breaking of an anomalous global symmetry (PQ symmetry) generates a pseudo-Nambu-Goldstone boson called axion, which is also a dark matter candidate. One problem for PQ mechanism is that Planck-suppressed operators which explicitly violate PQ symmetry can easily generate non-zero effective theta angle exceeding the experimental limit. This issue is known as the axion quality problem. To avoid this problem, several models with higher-energy dynamics are proposed. Among them are composite axion models, in which PQ symmetry is spontaneously broken by hidden strong dynamics in high-energy, resulting in the axion emerging as a composite state. In models with such high-energy dynamics, calculating the axion mass solely within QCD may be insufficient, since small instantons in higher-energy dynamics could, in principle, enhance the axion mass. However, in my presentation, I will explain that in some specific composite axion models addressing the quality problem, small instantons do not enhance the axion mass, even in cases where the axion mass enhancement seems possible naively. This talk is based on 2404.19342 [hep-ph]
