Tri-bimaximal mixing and the neutrino oscillation data

Abstract Following recent results from the SNO solar neutrino experiment and the K2K long-baseline neutrino experiment, the combined existing data on neutrino oscillations now point strongly to a specific form for the lepton mixing matrix, with effective bimaximal mixing of ν μ and ν τ at the atmospheric scale and effective trimaximal mixing for ν e with ν μ and ν τ at the solar scale (hence ‘tri-bimaximal’ mixing). We give simple mass-matrices leading to tri-bimaximal mixing, and discuss its relation to the Fritzsch–Xing democratic ansatz.