Day-Night and Energy Variations for Maximal Neutrino Mixing Angles

It has been stated in the literature that the case of maximal mixing angle for nue leads to no day-night effect for solar neutrinos and an energy independent flux suppression of 12. While the case of maximal mixing angle and delta square m in the MSW range of parameter space does lead to suppression of the electron neutrinos reaching the earth from the sun by Psub s 12 the situation is different for neutrinos that have passed through the earth. We make the point that at maximal mixing, just as with smaller mixing angles, the earth regenerates the nu1 state from the predominantly nu2 state reaching the earth, leading to coherent interference effects. This regeneration can lead to a day-night effect and an energy dependence of the suppression of solar electron neutrinos, even for the case of maximal mixing. For large mixing angles, the energy dependence of the day-night asymmetry depends heavily on delta square m. With a sufficiently sensitive measurement of the day-night effect, this energy dependence could be used to distinguish among the large mixing angle solutions of the solar neutrino problem.