Confirming the existence of the strong CP problem in lattice QCD with the gradient flow

Abstract

We calculate the electric dipole moment of the nucleon induced by the quantum chromodynamics θ term. We use the gradient flow to define the topological charge and use Nf=2+1 flavors of dynamical quarks corresponding to pion masses of 700, 570, and 410MeV, and perform an extrapolation to the physical point based on chiral perturbation theory. We perform calculations at three different lattice spacings in the range of 0.07fm <1.98×10-10 (90% CL). A first attempt at calculating the nucleon Schiff moment in the continuum resulted in Sp=0.50(59)×10-4θ¯efm3 and Sn=-0.10(43)×10-4θ¯efm3.