arXiv subjects
Publications and source records attributed to N. Cosme.
We discuss leptogenesis in its natural context, i.e. gauge unification, by including in the analysis the effects of the gauge sector associated to the Majorana neutrinos. It results in stricter bounds on the minimal Majorana mass, depending on the gauge bosons mass, but also prevents to deduce any lower limit on the Yukawa couplings since thermal and re-heating scenarios are now indistinguishable.
Leptogenesis is considered in its natural context where Majorana neutrinos fit in a gauge unification scheme and therefore couple to some extra gauge bosons. The masses of some of these gauge bosons are expected to be similar to those of the heavy Majorana particles, and this can have important consequences for leptogenesis. In fact, the effect can go both ways. Stricter bounds are obtained on one hand due to the dilution of the CP-violating effect by new decay and scattering channels, while, in a re-heating scheme, the presence of gauge couplings facilitates the re-population of the Majorana states. The latter effect allows in particular for smaller Dirac couplings.
We present a mechanism to generate complex phases from real 4+1 dimensional couplings in a model of weak interactions through dimensional reduction of a gauge theory. The orbifolding of a 4+1 dimensional Sp(4) \times U(1) group is the minimal setup which provides both CP violation and an SU(2) \times U(1) structure. We show that grand unification requires at least SO(11).
We provide simple examples of the generation of complex mass terms and hence CP violation through dimensional reduction.
CP is a symmetry of pure gauge theories, that is without scalar interactions. Actually its violation originates in the Standard Model from the completely arbitrary Yukawa couplings. Thus, as the unification principle would wash out the arbitrariness of these couplings possibly relating them to the gauge interactions, the resulting theory should be expected as CP-invariant. According to this, a breaking mechanism of CP should then take place. We will explore here the possibility of CP breaking through the dimensional reduction process.
We study flavour neutrinos confined to our 4-dimensional world coupled to one "bulk" state, i.e. a Kaluza-Klein tower. We discuss the spatial development of the neutrino disappearance, the possibility of resurgence and the effective flavour transitions induced in this mechanism. We show that even a simple model can produce an energy-independent suppression at large distances, and relate this to experimental data.