This class performs the decay of a vector meson into two pseudo-scalars according to a flat phase space. If, however the decaying particle comes from a pseudo-scalar and has only one sibling which is a pseudo-scalar (or a photon) the decay is reweighted with cos^2 (sin^2 for photon) of the angle between one of the decay products and its grand parent.
See also ThePEG::V2PPDecayer