Full QCD calculation of neutron electric dipole moment with the external electric field method

TL;DR

This study computes the neutron electric dipole moment in full QCD using the external electric field method, revealing non-zero signals and unexpected quark mass dependence, challenging previous theoretical expectations.

Contribution

It presents the first lattice QCD calculation of neutron EDM with dynamical quarks using the external electric field method, highlighting novel findings on quark mass dependence.

Findings

Non-zero neutron and proton EDM signals detected.

Nucleon EDM does not decrease toward the chiral limit.

Discussion of possible reasons for unexpected behavior.

Abstract

We have calculated the neutron electric dipole moment (NEDM) in the presence of the CP violating $\theta$ term in lattice QCD with 2-flavor dynamical clover quarks, using the external electric field method. Accumulating a large number of statistics by the averages over 16 different source points and over forward and backward nucleon propagators, we have obtained non-zero signals of neutron and proton EDM beyond one standard deviation at each quark mass in full QCD. We have investigated the quark mass dependence of nucleon EDM in full QCD, and have found that nucleon EDM in full QCD does not decrease toward the chiral limit, as opposed to the theoretical expectation. We briefly discuss possible reasons for this behavior.