Softly broken μ⇆τ symmetry in the minimal seesaw model

Neutrino oscillations data indicates that neutrino mixings are consistent with an apparent nu(mu) - nu(tau) exchange symmetry in neutrino mass matrix. We observe that in the minimally extended standard model with the seesaw mechanism, one can impose mu <-> tau symmetry at the tree level on all Lagrangian terms, but for the mass difference among mu and tau leptons. In the absence of any new extra physics, this mass difference becomes the only source for the breaking of such a symmetry, which induces, via quantum corrections, small but predictable values for theta(13), and for the deviation of theta(ATM) from maximality. In the CP conserving case, the predictions only depend on neutrino mass hierarchy and may provide a unique way to test for new physics with neutrino experiments.