CP Violation and Leptogenesis

The origin of the baryon asymmetry of the Universe is one of the key open questions to be addressed in particle physics and cosmology. Assuming a negligible initial baryon asymmetry, its dynamical production can happen in presence of non-conservation of the baryon and/or lepton number, violation of the C and CP symmetries and out-of-equilibrium conditions. Leptogenesis is a mechanism, proposed in the context of see-saw models, which can satisfy all these requirements and explain the observed baryon asymmetry. In the simplest case of see-saw type I, in which right handed neutrinos, singlets of the Standard Model, are introduced, lepton number is violated by the heavy Majorana masses, in conjuction with the Yukawa couplings, CP can be violated by complex terms in the Dirac masses and the out-of equilibrium condition is satisfied by the decays of the right handed neutrinos, when the temperature drops below their mass. The interesting question arises if the observable low energy CP violation, parameterised by the δ phase and measurable in long baseline neutrino oscillation experiments, can be responsible for the baryon asymmetry. Although in a model independent way it is not possible to draw such connection, we show that, in presence of flavour effects in leptogenesis, the δ phase enters directly in the lepton, and baryon, asymmetry and thanks to the large value of θ13 it may be at the origin of the matter-antimatter asymmetry we observe.