On the Domain of Mixing Angles in Three Flavor Neutrino Oscillations

We clarify the domain needed for the mixing angles in three flavor neutrino oscillations. By comparing the ranges of the transition probabilities as functions of the domains of the mixing angles, we show that it is necessary and sufficient to let all mixing angles be in $[0,\pi \mathrm{/}2]$. This holds irrespectively of any assumptions on the neutrino mass squared differences.