Leptogenesis and the small-angle MSW solution

摘要

The lepton asymmetry created in the out-of-equilibrium decay of a heavy Majorana neutrino can generate the cosmological baryon asymmetry Y-B when processed through fast anomalous electroweak reactions. In this work I examine this process under the following assumptions: (1) maximal nu(mu)- -nu(tau) mixing (2) hierarchical mass spectrum m(3) similar or equal to 5 x 10(-2) eV much greater than m(2) (3) small-angle MSW solution to the solar neutrino deficit. Working in a basis where the charged lepton and heavy neutrino mass matrices are diagonal, I find the following bounds on the heavy Majorana masses M-i: (a) for a symmetric Dirac neutrino mass matrix (no other constraints), a Y-B compatible with BBN constraints can be obtained for min(M-2,M-3) > 10(11) GeV (b) if any of the Dirac matrix elements vanishes, successful baryogenesis can be effected for a choice of min(M-2,M-3) as low as a few x 10(9) GeV. The latter is compatible with reheat requirements for supersymmetric cosmologies with sub-TeV gravitino masses. (C) 2000 Published by Elsevier Science B.V. All rights reserved. References: 62