We investigate the viability of thermal leptogenesis in type-I seesaw models with leptonic flavor symmetries that lead to tribimaximal neutrino mixing. We consider an effective theory with an $A_4\times Z_3\times Z_4$ symmetry, which is spontaneously broken at a scale much higher than the electroweak scale. At the high scale, leptonic Yukawa interactions lead to exact tribimaximal mixing and the heavy Majorana neutrino mass spectrum is exactly degenerate. In this framework, leptogenesis becomes viable once this degeneracy is lifted either by renormalization group effects or by a soft breaking of the $A_4$ symmetry. The implications for low-energy neutrino physics are discussed.

• Received 23 April 2009

DOI:https://doi.org/10.1103/PhysRevD.79.093008