The electric dipole moment of the neutron from 2+1 flavor lattice QCD

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We compute the electric dipole moment dₙ of the neutron from a fully dynamical simulation of lattice QCD with 2+1 flavors of clover fermions and nonvanishing theta term. The latter is rotated into the pseudoscalar density in the fermionic action using the axial anomaly. To make the action real, the vacuum angle theta is taken to be purely imaginary. The physical value of dₙ is obtained by analytic continuation. We find dₙ = -3.8(2)(9) x 10⁻¹⁶ [theta e cm], which, when combined with the experimental limit on dₙ, leads to the upper bound theta < 7.6 x 10⁻¹¹.