Jordy de Vries — Page 4

arXiv2015

The nucleon electric dipole moment with the gradient flow: the $θ$-term contribution

We propose a new method to calculate electric dipole moments induced by the strong QCD $θ$-term. The method is based on the gradient flow for gauge fields and is free from renormalization ambiguities. We test our method by computing the nucleon electric dipole moments in pure Yang-Mills theory at several lattice spacings, enabling a first-of-its-kind continuum extrapolation. The method is rather general and can be applied for any quantity computed in a $θ$ vacuum. This first application of the gradient flow has been successful and demonstrates proof-of-principle, thereby providing a novel method to obtain precise results for nucleon and light nuclear electric dipole moments.

hep-lat↗

arXiv2014

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 $\bar{g}_π^{(1)}$ 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 $\bar{g}_π^{(1)}$-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 $\bar{g}_π^{(1)}$ 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 $|\bar{g}_π^{(1)}| \lesssim 1.1\times 10^{-10}$.

nucl-th↗