mu-tau Interchange symmetry and lepton mixing

Understand

We focus on the use of a mu-tau interchange symmetry to explain features of lepton mixing, especially maximal atmospheric neutrino mixing.

• We review two models which achieve this goal and are based on the seesaw mechanism and on the soft breaking of the family-lepton-number symmetries.
• We also note that that symmetry may be embedded in a generalized CP symmetry.
• We show that, in the context of some of our models, arguments of naturalness may be used for explaining the smallness of the mass ratio m_mu / m_tau.