The electric dipole form factor of the nucleon

The electric dipole form factor of the nucleon stemming from the QCD θ¯ term is calculated in chiral perturbation theory in leading order. To this order, the form factor originates from the pion cloud. Its momentum-dependence 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.