Neutron and proton electric dipole moments fromNf=2+1domain-wall fermion lattice QCD

Abstract

We present a lattice calculation of the neutron and proton electric dipole moments (EDM's) with N f = 2 + 1 flavors of domain-wall fermions. The neutron and proton EDM form factors are extracted from three-point functions at the next-to-leading order in the θ vacuum of QCD. In this computation, we use pion masses of 0.33 and 0.42 GeV and 2.7 fm 3 lattices with Iwasaki gauge action and a 0.17 GeV pion and 4.6 fm 3 lattice with I-DSDR gauge action, all generated by the RBC and UKQCD collaborations. The all-mode-averaging technique enables an efficient and high statistics calculation. Chiral behavior of lattice EDM's is discussed in the context of baryon chiral perturbation theory. In addition, we also show numerical evidence on the relationship of threeand two-point correlation functions with the local topological charge distribution.

Theta dependence in holographic QCD

“…Expanding the action to second order in derivatives, considering the UV asymptotics U → ∞ and integrating over the compact x 4 direction one gets the Yang-Mills Lagrangian 9) and k is an integer. The second relation in (2.9) defines θ mod 2π integer shifts (since the integral of C 1 is gauge invariant only modulo 2πZ).…”

“…[8] for a detailed review on the subject), lattice estimates of CP-breaking observables in full QCD, notably estimates of the NEDM (see e.g. [9][10][11][12]), are still plagued by quite large systematic and statistical errors.…”

Neutron Electric Dipole Moment on the Lattice

“…Most previous calculations did not correctly account for this subtlety [31]. The problem can be corrected retroactively, and in Figure 3 we show the resulting reduction in the value reported in recent calculations [26,27]). …”

“…Hence it can be treated as a small expansion parameter. Any expectation value in presence of a small QCD Θ-term can then be written as follows [23][24][25][26][27]:…”

“…We illustrate these three approaches for the case of the CP-violating Θ-term whose volume integral is the topological charge Q top . They are the external electric field method [19][20][21][22], expansion in θ [23][24][25][26][27], and simulation with imaginary θ [28][29][30].…”