Tri-Bimaximal Mixing and the Neutrino Oscillation Data

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 ${\nu }_{\mu }$ and ${\nu }_{\tau }$ at the atmospheric scale and effective trimaximal mixing for ${\nu }_e$ with ${\nu }_{\mu }$ and ${\nu }_{\tau }$ 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.