Calculation of the neutron electric dipole moment with two dynamical flavors of domain wall fermions

We present a study of the neutron electric dipole moment ((d) over right arrow (N)) within the framework of lattice QCD with two flavors of dynamical light quarks. The dipole moment is sensitive to the topological structure of the gauge fields, and accuracy can only be achieved by using dynamical, or sea quark, calculations. However, the topological charge evolves slowly in these calculations, leading to a relatively large uncertainty in (d) over right arrow (N). It is shown, using quenched configurations, that a better sampling of the charge distribution reduces this problem, but because the CP even part of the fermion determinant is absent, both the topological charge distribution and (d) over right arrow (N) are pathological in the chiral limit. We discuss the statistical and systematic uncertainties arising from the topological charge distribution and unphysical size of the quark mass in our calculations and prospects for eliminating them. Our calculations employ the RBC collaboration two flavor domain wall fermion and DBW2 gauge action lattices with inverse lattice spacing a(-1)approximate to 1.7 GeV, physical volume V approximate to(2 fm)(3), and light quark mass roughly equal to the strange quark mass (m(sea)=0.03 and 0.04). We determine a value of the electric dipole moment that is zero within (statistical) errors, from which we obtain the bound parallel to(d) over right arrow (N)parallel to less than or similar to 0.02e-theta-fm. Satisfactory results for the magnetic and electric form factors of the proton and neutron are also obtained and presented.