The Axion Quality and Fifth Force

Abstract

We investigate what it takes for the axion to address the strong CP problem in the presence of explicit Peccei-Quinn (PQ) symmetry breaking effects besides the strong interaction. In cases where the PQ-Higgsing scalar field directly couples to the Standard Model sector, it is pointed out that existing fifth force experiments can set better constraints on the axion quality over neutron electric dipole moment.

Comments: 10 pages, 1 figure. v2: Corrected the comment on equivalence principle in case 2, and a few typos. Main results unchanged