Speaker
Description
PQ solution to the strong CP problem probably encounters the axion domain wall problem. In this article, we propose a simple and testable solution, assuming that the U(1)PQU(1)PQ possesses mixed anomaly to a hidden SU(Nc)SU(Nc) color. Then, the axion field receives a new cosine potential from the hidden instantons, which breaks the ZNDWZNDW subgroup explicitly. The new potential lifts the vacua degeneracy, but also drives the effective θθ angle away from the origin, re-incuring the strong CP problem. However, we find that the dark QCD scale within the 0.1 to 3 MeV window survives, maintaining a delicate balance. Two observational signatures are explored: gravitational waves from domain wall collapse, already probed by current PTAs, and di-photon signals from axion-dark-glueball mixing, which require next-generation MeV telescopes. The scenario favors a cold dark QCD sector consistent with dark glueball relic constraints.
