Neutron electric dipole moment with two flavors of domain wall fermions

Abstract

We present a study of the neutron electric dipole moment ( ~ dN) within the framework of lattice QCD with two flavors of light quarks. The dipole moment is sensitive to the topological structure of the gauge fields, so accuracy can only be achieved by using dynamical, or sea quark, calculations. The topological charge (distribution) evolves slowly in these calculations, leading to systematic uncertainty in ~ dN. It is shown, using quenched configurations, that a better sampling of the charge distribution eliminates this problem, but because the CP even part of the fermion determinant is absent, both the topological charge distribution and ~ dN are pathological in the chiral limit. We discuss the systematic uncertainties arising from the topological charge distribution and unphysical quark mass in our calculations and prospects for eliminating them. Our calculations are done using two flavors of domain wall fermions and the DBW2 gauge action with inverse lattice spacing a 1 1.7 GeV, physical volume V (2 fm) 3 , and light quark mass roughly equal to the strange quark mass. The systematic uncertainties described above notwithstanding, we find |~ dN|= 10(11)◊10 15 eq cm. The central value translates into the bound q < 6.3◊ 10 11 on the fundamental CP-odd parameter in the QCD lagrangian when combined with the current experimental bound on |~N|. The quoted error is statistical only. Satisfactory results for the magnetic dipole moments and electromagnetic form factors of the proton and neutron are also obtained.