Note on the strong CP problem from a 5-dimensional perspective

Understand

We consider 5 dimensional gauge theories where the 5th direction is compactified on an interval.

• The Chern-Simons (CS) terms (favored by naive dimensional analysis) are discussed.
• A simple scenario with an extra U(1)_X gauge field that couples to SU(3)_{color} through a CS term in the bulk is constructed.
• The extra component of the Abelian gauge field plays a role of the axion, which in the standard manner solves the strong CP problem easily avoiding most of experimental constraints.