Cosmic microwave background, matter–antimatter asymmetry and neutrino masses Original Research Article

We study the implications of thermal leptogenesis for neutrino parameters. Assuming that decays of N1, the lightest of the heavy Majorana neutrinos, initiate baryogenesis, we show that the final baryon asymmetry is determined by only four parameters: the CP asymmetry ε1, the heavy neutrino mass M1, the effective light neutrino mass m1, and the quadratic mean m of the light neutrino masses. Imposing the CMB measurement of the baryon asymmetry as constraint on the neutrino parameters, we show, in a model independent way, that quasi-degenerate neutrinos are incompatible with thermal leptogenesis. For maximal CP asymmetry ε1, and neutrino masses in the range from (Δm2sol)1/2 to (Δm2atm)1/2, the baryogenesis temperature is TB=O(1010) GeV.