Patterns in the fermion mixing matrix, a bottom-up approach

We first obtain the most general and compact parametrization of the unitary transformation diagonalizing any 3x3 Hermitian matrix H, as a function of its elements and eigenvalues. We then study a special class of fermion mass matrices, defined by the requirement that all of the diagonalizing unitary matrices (in the up, down, charged lepton, and neutrino sectors) contain at least one mixing angle much smaller than the other two. Our new parametrization allows us to quickly extract information on the patterns and predictions emerging from this scheme. In particular we find that the phase difference between two elements of the two mass matrices (of the sector in question) controls the generic size of one of the observable fermion mixing angles: i.e. just fixing that particular phase difference will predict the generic value of one of the mixing angles, irrespective of the value of anything else.