Mu-tau antisymmetry and neutrino mass matrices
  Using the seesaw mechanism and a discrete symmetry, we construct a class of models for the neutrino mass matrix where the inverse of that matrix is the sum of a mu-tau antisymmetric background and a perturbation. We consider various possibilities for that perturbation. The simplest possible perturbations lead to four-parameter neutrino mass matrices which are unable to fit the experimental data. More complicated perturbations give rise to viable six-parameter mass matrices; we present detailed predictions of each of them. 
Walter Grimus, Satoru Kaneko, Luis Lavoura, Hideyuki Sawanaka,   Morimitsu Tanimoto