Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses
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We study the implications of thermal leptogenesis for neutrino parameters. Assuming that decays of N_1, 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 epsilon_1, the heavy neutrino mass M_1, the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{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 epsilon_1, and neutrino masses in the range from (Δm^2_{sol})^{1/2} to (Δm^2_{atm})^{1/2}, the baryogenesis temperature is T_B = O(10^{10}) GeV.
28 pages, 14 figures included; v2: erratum added, M_1 lower bound in the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/3
28 pages, 14 figures included; v2: erratum added, M_1 lower bound in the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/3