Nucleon Electric Dipole Moments and the Isovector Parity- and Time-Reversal-Odd Pion-Nucleon Coupling

Understand

The isovector time-reversal- and parity-violating pion-nucleon coupling $\bar{g}_{\pi}^{(1)}$ 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 $\bar{g}_{\pi}^{(1)}$-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 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 $\bar{g}_{\pi}^{(1)}$ is suppressed, implying more relaxed constraints on the parameter space of the left-right symmetric model.