Nonthermal leptogenesis with almost degenerate superheavy neutrinos

We present a model with minimal assumptions for nonthermal leptogenesis with almost degenerate superheavy right-handed neutrinos in a supersymmetric setup. In this scenario the gauge singlet inflaton is directly coupled to the right-handed ~s!neutrinos with a mass heavier than the inflaton mass. This helps to avoid potential problems which can naturally arise otherwise. The inflaton decays into standard model leptons and Higgs bosons via off-shell right-handed ~s!neutrinos and reheats the Universe. The same channel is also responsible for generating the lepton asymmetry, thus requiring no stage of preheating in order to excite superheavy ~s!neutrinos. The suppressed decay rate of the inflaton naturally leads to a sufficiently low reheat temperature, which in addition, prevents any wash out of the yielded asymmetry. We will particularly elaborate on important differences from leptogenesis with on-shell ~s!neutrinos. It is shown that for nearly degenerate neutrinos a successful leptogenesis can be accommodated for a variety of inflationary models with a rather wide ranging inflationary scale.