Constraints on three-neutrino mixing from atmospheric and reactor data.

Observations of atmospheric neutrinos are usually analyzed using the simplifying approximation that either ν µ ↔ ν τ or ν e ↔ ν µ two-flavor mixing is relevant. Here we instead consider the data using the simplifying approximation that only one neutrino mass scale is relevant. This approximation is the minimal three-flavor notation that includes the two relevant two-flavor approximations. The constraints in the parameter space orthogonal to the usual, two-flavor analyses are studied.