The electric dipole form factor of the nucleon in chiral perturbation theory to sub-leading order

Abstract

The electric dipole form factor (EDFF) of the nucleon stemming from the QCD θ¯ term and from the quark color-electric dipole moments is calculated in chiral perturbation theory to sub-leading order. This is the lowest order in which the isoscalar EDFF receives a calculable, non-analytic contribution from the pion cloud. In the case of the θ¯ term, the expected lower bound on the deuteron electric dipole moment is |dd|≳1.4⋅10−4θ¯e fm. The momentum dependence of the isovector EDFF is proportional to a non-derivative time-reversal-violating pion-nucleon coupling, and the scale for momentum variation—appearing, in particular, in the radius of the form factor—is the pion mass.