Strong CP breaking and quark-antiquark repulsion in QCD, at finite theta

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