Unitarity Quadrangles of Four Neutrino Mixing

Abstract

We present a classification of the unitarity quadrangles in the four-neutrino mixing scheme. We find that there are totally thirty-six distinct topologies among twelve different unitarity quadrangles. Concise relations are established between the areas of those unitarity quadrangles and the rephasing invariants of CP and $T$ violation.

RevTex 10 pages. Minor changes made. Accepted for publication in Phys. Rev. D