Phenomenology of maximal and near-maximal lepton mixing - art. no. 013007

The possible existence of maximal or near-maximal lepton mixing constitutes an intriguing challenge for fundamental theories of flavor. We study the p henomenological consequences of maximal and near-maximal mixing of the elec tron neutrino with other (x=tau and/or muon) neutrinos. We describe the dev iations from maximal mixing in terms of a parameter epsilon =1-2 sin(2) the ta (ex) and quantify the present experimental status for \epsilon\<0.3. We show that both probabilities and observables depend on <epsilon> quadratica lly when effects are due to vacuum oscillations and they depend on epsilon linearly if matter effects dominate. The most important information on nu ( e) mixing comes from solar neutrino experiments. We find that the global an alysis of solar neutrino data allows maximal mixing with confidence level b etter than 99% for 10(-8) eV(2) less than or similar to Deltam(2) less than or similar to x 10(-7) eV(2). In the mass ranges Deltam(2)greater than or similar to1.5 x 10(-5) eV(2) and 4 x 10(-10) eV(2) less than or similar to Delta m(2) x 10(-7) eV(2) the full interval \epsilon\<0.3 is allowed within <similar to>4 sigma (99.995% CL) We suggest ways to measure epsilon in fut ure experiments. The observable that is most sensitive to epsilon is the ra te [NC]/[CC] in combination with the day-night asymmetry in the SNO detecto r. With theoretical and statistical uncertainties, the expected accuracy af ter 5 years is Delta epsilon similar to 0.07. We also discuss the effects o f maximal and near-maximal nu (e) mixing in atmospheric neutrinos, supernov a neutrinos, and neutrinoless double beta decay.