An extension of the SM based on effective Peccei-Quinn Symmetry

Understand

Peccei-Quinn (PQ) mechanism based on a chiral global U(1) symmetry is considered to be a simple and elegant solution for strong CP problem.

• Fact that the mechanism could be experimentally examined through the axion search makes it much more interesting and recently it causes a lot of attention again.
• However, it is also known that the mechanism is annoyed by two serious problems, that is, a domain wall problem and goodness of global symmetry.
• Any global symmetry is considered not to be exact due to the quantum effect of gravity.