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

Abstract

We have calculated the neutron electric dipole moment (EDM) in the presence of the CP violating term in lattice QCD with two-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 nonzero signals of neutron and proton EDM beyond 1 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.

Nuclear electric dipole moments in chiral effective field theory

“…The neutron and proton EDMs induced by the θ-term have recently been calculated in refs. [48,49] on the basis of supplementary Lattice-QCD input [50][51][52],…”

Direct and indirect constraints on CP-violating Higgs-quark and Higgs-gluon interactions

“…Currently the effect of θ ind is taken into account within the QCD sum rule approach. Progress in lattice-QCD evaluations of dn(θ) (for recent results see [63][64][65]) will also improve the contribution to the nucleon EDM proportional toθ ind .…”

New Physics Searches from Nucleon Matrix Elements in Lattice QCD

“…So far we discussed the extraction of the nEDM from the CP-odd form factor [47,[50][51][52], which is based on the small-θ expansion. However, there are alternative methods to compute the nEDM, such as, simulating the action with an imaginary θ [53], or with an application of an external electric field and measuring the associated energy shifts [54]. Lattice results extracted from all the aforementioned methods are collected in Fig.…”

“…The large statistical error is a demonstration of the difficulty to extract this quantity and the need for development of new techniques. π for: a) N f =2+1+1 TMF [47] (blue square) corresponding to a weighted average using different methods for extracting F 3 (0)), b) N f =0 DWF [50] (magenta upward triangles), N f =2+1 DWF [51] (red circles) and N f =0 Clover fermions [52] (green downward triangles) by extracting the CP-odd F 3 (Q 2 ) and fitting its Q 2 -dependence, c) N f =2 Clover fermions [54] (turquoise left triangles) obtained using a background electric field, d) N f =2+1 Clover fermions [53] (orange diamonds) by implementing an imaginary θ.…”