News on Leptogenesis

The possibility to explain the CMB measurement of the baryon asymmetry with leptogenesis results in a stringent bound on the neutrino masses such that [(m_1)^2+(m_2)^2+(m_3)^2]^(1/2) < 0.30 eV. We discuss the implications of such a bound for future experiments on the absolute neutrino mass scale.Comment: 12 pages, 4 figures included. Talk given at the Third Tropical Workshop: Neutrinos, Branes and Cosmology, 19-23 August 2002, San Juan, Puerto Rico. v2 references adde

The cosmological information on neutrino mixing

Cosmology provides interesting information on neutrino mixing models with sterile neutrinos. In this case non standard BBN effects can be relevant. We show how the recent measurement of the baryon content from the observations of CMB anisotropies together with the primordial nuclear abundances measurements can be used to constrain them. In particular four neutrino mixing models are potentially at variance with the cosmological observations. We also discuss the possible scenarios from future experiments.Comment: 5 pages, LaTeX, JHEP style, talk given at EPS HEP 2001, Budapest, Hungary, 12 - 18 July 200

Flavoured leptogenesis: a successful thermal leptogenesis with N_1 mass below 10^8 GeV

We prove that taking correctly into account the lepton flavour dependence of the CP asymmetries and washout processes, it is possible to obtain successful thermal leptogenesis from the decays of the second right-handed neutrino. The asymmetries in the muon and tau-flavour channels are then not erased by the inverse decays of the lightest right-handed neutrino, N_1. In this way, we reopen the possibility of ``thermal leptogenesis'' in models with a strong hierarchy in the right-handed Majorana masses that is typically the case in models with up-quark--neutrino Yukawa unification.Comment: 5 pages, no figures. References added, referencing correcte

The Neutrino Mass Window for Baryogenesis

Interactions of heavy Majorana neutrinos in the thermal phase of the early universe may be the origin of the cosmological matter-antimatter asymmetry. This mechanism of baryogenesis implies stringent constraints on light and heavy Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry in heavy neutrino decays which, together with the kinetic equations, yields an upper bound on all light neutrino masses of 0.1 eV. Lepton number changing processes at temperatures above the temperature T_B of baryogenesis can erase other, pre-existing contributions to the baryon asymmetry. We find that these washout processes become very efficient if the effective neutrino mass \tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial conditions is then erased. Hence, for neutrino masses in the range from (\Delta m^2_sol)^{1/2} \simeq 8*10^{-3} eV to (\Delta m^2_atm)^{1/2} \simeq 5*10^{-2} eV, which is suggested by neutrino oscillations, leptogenesis emerges as the unique source of the cosmological matter-antimatter asymmetry.Comment: 29 pages, 12 figures include

Some Aspects of Thermal Leptogenesis

Properties of neutrinos may be the origin of the matter-antimatter asymmetry of the universe. In the seesaw model for neutrino masses this leads to important constraints on the properties of light and heavy neutrinos. In particular, an upper bound on the light neutrino masses of 0.1 eV can be derived. We review the present status of thermal leptogenesis with emphasis on the theoretical uncertainties and discuss some implications for lepton and quark mass hierarchies, CP violation and dark matter. We also comment on the `leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in the range where leptogenesis works best.Comment: 23 pages, 5 figures, submitted to the Focus on Neutrino Physics issue of the New Journal of Physics, edited by F. Halzen, M. Lindner and A. Suzuk

Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses

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 (\Delta m^2_{sol})^{1/2} to (\Delta m^2_{atm})^{1/2}, the baryogenesis temperature is T_B = O(10^{10}) GeV.Comment: 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/