Axion quality problem alleviated by nonminimal coupling to gravity
Axion quality problem alleviated by nonminimal coupling to gravity
Global symmetries are expected to be violated by gravity, which may cause a serious problem to models based on these symmetries. A famous example is the Peccei-Quinn solution to the strong CP problem in QCD axion models; it requires a global U(1) symmetry to be respected with high quality, and …