Nucleon electric dipole moments and the isovector parity- and time-reversal-odd pion–nucleon coupling

The isovector time-reversal-and parity-violating pion-nucleon coupling (1) is uniquely sensitive to dimension-six interactions between right-handed light quarks and the Standard Model Higgs doublet that naturally arises in left-right symmetric models. Recent work has used the (1) -induced one-loop contribution to the neutron electric dipole moment d n , together with the present experimental d n bound, to constrain the CP-violating parameters of the left-right symmetric model. We show that this and related analyses are based on an earlier meson theory d n computation that is not consistent with the powercounting appropriate for an effective field theory. We repeat the one-loop calculation using heavy baryon chiral perturbation theory and find that the resulting d n sensitivity to (1) is suppressed, implying more relaxed constraints on the parameter space of the left-right symmetric model. Assuming no cancellations between this loop contribution and other contributions, such as the leading order EDM low-energy constant, the present limit on d n implies | (1) | 1.1 10 -10 .