How good is μ-τsymmetry after results on non-zero θ₁₃?

الأصل · EN

Viability of the μ-τinterchange symmetry imposed as an approximate symmetry (1) on the neutrino mass matrix Mνf in the flavour basis (2) simultaneously on the charged lepton mass matrix Mₗ and the neutrino mass matrix Mνand (3) on the underlying Lagrangian is discussed in the light of recent observation of a non-zero reactor mixing angle θ₁₃. In case (1), μ-τsymmetry breaking may be regarded as small (less than 20-30%) only for the inverted or quasidegenerate neutrino mass spectrum and the normal hierarchy would violate it by a large amount. The case (2) is more restrictive and the requirement of relatively small breaking allows only the quasidegenerate spectrum. If neutrinos obtain their masses from the type-I seesaw mechanism then small breaking of the μ-τsymmetry in the underlying Lagrangian may result in a large breaking in Mνf and even the hierarchical neutrino spectrum may also be consistent with mildly broken μ-τsymmetry of the Lagrangian. Neutrinoless double beta decay provides a good means of distinguishing above scenarios. In particular, non-observation of signal in future experiments such as GERDA would rule out scenarios (1) and (2).