Gravitino leptogenesis

We explore here a new mechanism by which the out of equilibrium decay of heavy gravitinos, followed by possible R-parity violating decays in the minimal supersymmetric standard model (MSSM), can generate the baryon asymmetry of the Universe. In this mechanism, gravitino decay produces a CP asymmetry that is carried by squarks or sleptons. These particles then decay through R-parity violating operators generating a lepton asymmetry. The lepton asymmetry is converted into a baryon asymmetry by weak sphalerons, as in the familiar case of leptogenesis by Majorana neutrino decays. To ensure that the gravitino decays while the sphaleron is still in equilibrium, we obtain a lower bound on the gravitino mass, m3/2â‰108 GeV, and therefore our mechanism requires a high scale of Supersymmetry (SUSY) breaking, as well as a minimum reheating temperature after inflation of Tâ‰1012 GeV in order for the gravitino density to be sufficiently large to generate the baryon asymmetry today. We consider each of the MSSM's relevant R-parity violating operators in turn, and we derive constraints on parameters in order to give rise to a baryon asymmetry comparable to that observed today, consistent with low energy phenomenological bounds on SUSY models. Interestingly, R-party violating terms that can produce a viable baryon asymmetry via the mechanism we explore can also radiatively produce neutrino masses corresponding to the observed magnitude, providing a new possible connection between neutrino mass generation and the origin of the baryon asymmetry today.