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 (g) over bar ((1))(pi) 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 (g) over bar ((1))(pi)-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 power-counting 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 (g) over bar ((1))(pi) pis 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 vertical bar(g) over bar ((1))(pi)vertical bar less than or similar to 1.1 x 10(-10). (C) 2014 The Authors. Published by Elsevier B.V.