Distinguishing axions from generic light scalars using EDM and   fifth-force experiments
  We derive electric dipole moment (EDM) constraints on possible new macroscopic time reversal and parity violating (TVPV) spin-dependent forces. These constraints are compared to those derived from direct searches in fifth-force experiments and from combining laboratory searches with astrophysical bounds on stellar energy loss. For axion-mediated TVPV spin-dependent forces, EDM constraints dominate over fifth-force limits by several orders of magnitude. However, we show that for a generic light scalar, unrelated to the strong CP problem, present bounds from direct fifth- force searches are more stringent than those inferred from EDM limits, for the interaction ranges explored by fifth-force experiments. Thus, correlating observations in EDM and fifth-force experiments could help distinguish axions from more generic light scalar scenarios. 
Sonny Mantry, Mario Pitschmann, Michael J. Ramsey-Musolf
hep-ph hep-ex nucl-ex