Effects for atmospheric neutrino experiments from electron neutrino oscillations

The minimal interpretation of the atmospheric neutrino data suggests that the muonneutrino oscillates into another species with a mixing angle close to the maximal $\pi/4$. In the Exact Parity Symmetric Model, both the muon and electron neutrinos are expected to be maximally mixed with essentially sterile partners ($\nu'_{\mu}$ and $\nu'_e$ respectively). We examine the impact of maximal $\nu_e - \nu'_e$ oscillations on the atmospheric neutrino experiments. We argue that the present data suggests the operation of both $\nu_{\mu}-\nu'_{\mu}$ and $\nu_e-\nu'_e$ oscillations. This interpretation can be further tested by Superkamiokande, which should be sensitive to the effect of maximal $\nu_e - \nu'_e$ oscillations on atmospheric neutrino data for $\delta m^2 \ (\nu_e - \nu_e')$ in the approximate range $7 \times 10^{-5} \ eV^2 < |\delta m^2| < 10^{-3} \ eV^2$. For $\delta m^2$ in this range, a distinctive rise in the ratio of muon-like to electron-like events is predicted for the low-energy sample. Furthermore, the ratio of low-energy electron-like events with zenith angles less than $90\deg$ to those with zenith angles greater than $90\deg$ should be greater than 1.