  This work is devoted to the study of the CP-breaking dynamics in QCD, at
finite theta-angle. By working in the semi-classical limit, in which the
topology of the vacuum is clustered around instantons and anti-instantons, we
show that quantum fluctuations of the theta-vacuum generate an effective
flavor-dependent repulsion between matter and anti-matter, inside hadrons. As a
consequence, during the tunneling between the degenerate vacua, quarks and
anti-quarks in the neutron migrate in opposite directions, giving rise to an
oscillating electric dipole moment. We discuss a possible phenomenological
implication of this effect.
