1112.3628 (Julian Heeck et al.)

"Hidden" O(2) and SO(2) Symmetry in Lepton Mixing    [PDF]

Julian Heeck, Werner Rodejohann

To generate the minimal neutrino Majorana mass matrix that has a free solar
mixing angle and Delta m_sol^2 = 0 it suffices to implement an O(2) symmetry,
or one of its subgroups SO(2), Z_N (N>2), or D_N (N>2). This O(2) generalizes
the hidden Z_2^s of lepton mixing and leads in addition automatically to mu-tau
symmetry. Flavor-democratic perturbations, as expected e.g. from the Planck
scale, then result in tri-bimaximal mixing. We present a minimal model with
three Higgs doublets implementing a type-I seesaw mechanism with a spontaneous
breakdown of the symmetry, leading to large theta_13 and small Delta m_sol^2 =
0 due to the particular decomposition of the perturbations under mu-tau
symmetry.

View original: http://arxiv.org/abs/1112.3628