μ–τ symmetry in Zee–Babu model

Abstract

We study the Zee–Babu two-loop neutrino mass generation model and look for a possible flavor symmetry behind the tri-bimaximal neutrino mixing. We find that there probably exists the μ–τ symmetry in the case of the normal neutrino mass hierarchy, whereas there may not be in the inverted hierarchy case. We also propose a specific model based on a Froggatt–Nielsen-like Z5 symmetry to naturally accomplish the μ–τ symmetry on the neutrino mass matrix for the normal hierarchy case.