Time Reversal Violation in Nuclear Effective Field Theory

Abstract

The lack of invariance with respect to time reversal (T) of the weak interactions has long been known. However, T violation has yet to be observed from flavor-diagonal sources, where the primary quantities of interest are electric dipole moments (EDMs). Weak T violation gives EDMs that are far too small, but strong T violation via flavor-diagonal sources could give EDMs strong enough to be detected in the near future. It is thus important to understand precisely how various quark-level sources of T violation manifest themselves in hadronic physics.A useful technique for dealing with low-energy phenomena involving nucleons, nuclei, and various mesons, is effective field theory (EFT). The formalism and methodology of EFT are presented, followed by an introduction to the construction of chiral Lagrangians.A motivation for the study of T violation beyond the weak interactions is then given, with brief introductions to the most important sources of T violation.The QCD theta term is looked at using two differentapproaches. First, enforcing vacuum stability at quark level, a series of T-violating interactions ensue. Second, enforcing vacuum stability at hadronic level via field redefinitions, spurious interactions are demonstrated to be avoidable. Both approaches involve a constraining relationship between theta-term T violation and up-down quark-mass-difference isospin violation. The quark chromo-EDMs are shown to be identical to the theta term in their chiral symmetry properties. The quark EDMs and Weinberg operator,conversely, are shown to generate new interactions in addition to those generated by the theta term, differing nucleon EDM contributions in particular.The electric dipole form factor (EDFF) of the nucleon, with a theta term source, is calculated in both leading and subleading orders in chiral perturbation theory, with the momentum dependence at both orders given entirely by contributions from the pion cloud. Theleading result is purely isovector, while an isoscalar result appears in subleading order. The isoscalar EDM is used as a lower-bound estimate of the deuteron EDM. The momentum dependence of the EDFF for small momentum transfer is related to the electromagnetic nucleonSchiff moment, which is computed to subleading order.