Universal 2-3 symmetry

Abstract

Possible maximal mixing seen in the oscillations of the atmospheric neutrinos has led to postulate of a $μ$-$τ$ symmetry which interchanges $ν_μ$ and $ν_τ$. We argue that such symmetry need not be special to neutrinos but can be extended to all fermions. The assumption that all fermion mass matrices are approximately invariant under interchange of the second and the third generation fields is shown to be phenomenologically viable and has interesting consequences. In the quark sector, the smallness of $V_{ub}$ and $V_{cb}$ can be a consequences of this approximate 2-3 symmetry. The same approximate symmetry can simultaneously lead to large atmospheric mixing angle and can describe the leptonic mixing quite well provided the neutrino spectrum is quasi degenerate. We present this scenario, elaborate on its consequences and discuss its realization.