  Current neutrino oscillation data from solar, atmospheric, and reactor
experiments are consistent with the neutrino mixing matrix elements taking
values sin^2\theta_{12} = 1/3, sin^2\theta_{23} = 1/2, and sin^2\theta_{13}=0.
We present a class of renormalizable gauge models which realize such a
geometric mixing pattern naturally. These models, which are based on the
non--Abelian discrete symmetry A_4, place significant restrictions on the
neutrino mass spectrum, which we analyze. It is shown that baryogenesis via
leptogenesis occurs quite naturally, with a single phase (determined from
neutrino oscillation data) appearing in leptonic asymmetry and in neutrinoless
double beta decay. Such predicted correlations would provide further tests of
this class of models.
