Time-Reversal Violation in the Nucleon and Light Nuclei

Various experimental proposals promise significant advances in sensitivity to time-reversal (T) violation through measurements of electric dipole moments (EDMs) of the nucleon and light nuclei. The smallness of T-violation effects from the weak-interaction phase and the QCD vacuum angle suggests that Standard Model operators of effective dimension six (such as quark EDMs, and quark and gluon color-EDMs) may be important. The question then arises whether the dominant source of T violation, if any, can be inferred from measurements of hadronic and nuclear T-violating form factors (TVFFs). I argue that the answer is yes, because each T-violation source breaks the approximate chiral symmetry of QCD in a different way, and thus produces specific pion-nucleon interactions and, ultimately, different relations among observables. I present the chiral Lagrangian that incorporates all sources of dimension up to six and serves as a starting point for discussing T violation in the strong interactions at low energies. I give results for the TVFFs of the nucleon, deuteron, helion, and triton, ending with a discussion of open issues.