Leptogenesis, μ-τ symmetry and θ13

We show that in theories where neutrino masses arise from type I see-saw formula with three right-handed neutrinos and where large atmospheric mixing angle owes its origin to an approximate leptonic mu-tau interchange symmetry, the primordial lepton asymmetry of the Universe, epsilon(l) can be expressed in a simple form in terms of low energy neutrino oscillation parameters as epsilon(l) = (a Delta m(circle dot)(2) + b Delta m(A)(2)theta(2)(13)), where a and b are parameters characterizing high scale physics and are each of order <= 10(-2) eV(-2). We also find that for the case of two right-handed neutrinos, epsilon(l) proportional to theta(2)(13) as a result of which, the observed value of baryon to photon ratio implies a lower limit on theta(13). For specific choices of the CP phase delta we find theta(13) is predicted to be between 0.10-0.15. (c) 2005 Elsevier B.V. All rights reserved.