Day-night and energy dependence of MSW solar neutrinos for maximal mixing

It has been stated in the literature that the case of maximal mixing anglefor \nu_e leads to no day-night effect for solar neutrinos and an energyindependent flux suppression of 1/2. While the case of maximal mixing angle and\Delta m^2 in the MSW range does lead to suppression of the electron neutrinosreaching the earth from the sun by P_S=1/2, the situation is different forneutrinos that have passed through the earth. We make the pedagogical pointthat, just as with smaller mixing angles, the earth regenerates the |\nu_1>state from the predominantly |\nu_2 > state reaching the earth, leading tocoherent interference effects. This regeneration can lead to a day-night effectand an energy dependence of the suppression of solar electron neutrinos, evenfor the case of maximal mixing. For large mixing angles, the energy dependenceof the day-night asymmetry depends heavily on Delta m^2. With a sufficientlysensitive measurement of the day-night effect, this energy dependence could beused to distinguish among the large mixing angle solutions of the solarneutrino problem.Comment: JHEP style, 22 pages, 7 figures. References added, and minor rewordin