Z2 Symmetry Prediction for the Leptonic Dirac CP Phase
Abstract
Model-independent consequences of applying a generalized hidden horizontal Z2 symmetry to the neutrino mass matrix are explored. The Dirac CP phase deltaD can be expressed in terms of the three mixing angles as 4 ca sa cs ss sx cos deltaD = (s2s - c2s s2x) (c2a - s2a) where the si, ci are sines and cosines of the atmospheric, solar, and reactor angles. This relation is independent of neutrino masses and whether neutrinos are Dirac- or Majorana-type. Given the present constraints on the angles, deltaD is constrained to be almost maximal, a result which can be explored in experiments such as NOvA and T2K. The Majorana CP phases do not receive any constraint and are thus model-dependent. Also a distribution of thetax with a lower limit is obtained without specifying deltaD.