The forces mediated by spin-0 bosons are described, along with the existing experimental limits. The mass and couplings of the invisible axion are derived, followed by suggestions for experiments to detect axions via the macroscopic forces they mediate. In particular, novel tests of the $T$-violating axion monopole-dipole forces are proposed.

• Received 17 January 1984

DOI:https://doi.org/10.1103/PhysRevD.30.130