Leptogenesis, neutrino mixing data and the absolute neutrino mass scale.pdf

a r X i v : h e p - p h / 0 4 0 6 1 1 5 v 1 1 0 J u n 2 0 0 4 LEPTOGENESIS, NEUTRINO MIXING DATA AND THE ABSOLUTE NEUTRINO MASS SCALE a P. Di Bari IFAE, Universitat Auto?noma de Barcelona, 08193 Bellaterra (Barcelona), Spain Recent developments in thermal leptogenesis are reviewed. Neutrino mixing data favor a simple picture where the matter-anti matter asymmetry is generated by the decays of the heavy RH neutrinos mildly close to thermal equilibrium and, remarkably, in the full non relativistic regime. This results into predictions of the final baryon asymmetry not depending on the initial conditions and with minimized theoretical uncertainties. After a short outline of a geometrical derivation of the CP asymmetry bound, we derive analytic bounds on the lightest RH neutrino mass and on the absolute neutrino mass scale. Neutrino masses larger than 0.1 eV are not compatible with the minimal leptogenesis scenario. We discuss how the results get just slightly modified within the minimal supersymmetric standard model. In particular a conservative lower bound on the reheating temperature, TR 10 9 GeV, is obtained in the relevant effective neutrino mass range m?1 3×10 ?3 eV. We also comment on the existence of a ‘too-short-blanket problem’ in connection with the possibility of evading the neutrino mass upper bound. aCompendium of 1 and 2 mostly based on 3 with some new results in 3.4, 3.8 and 3.9. 1 Introduction Cosmic rays and CMBR observations indicate that our observable Universe is baryon asym- metric 4. Moreover the observation of the acoustic peaks in the power spectrum of CMBR 5, combined with large scale structures observations 6, provide a precise and robust mea- surement of such an asymmetry that can be expressed in terms of the baryon to photon number ratio at the recombination time, ηCMBB = (6.3 ± 0.3) × 10?10 , (1) in very good agreement with the latest determination from (NACRE updated) Standard BBN and primordial Deuterium measurements that give 7 ηS