  The rotational properties of angular momentum eigenstates imply the existence
of a frame-independent relation among the parameters of the decay distribution
of vector mesons into fermions. This relation is a generalization of the
Lam-Tung identity, a result specific to Drell-Yan production in perturbative
QCD, here shown to be equivalent to the dynamical condition that the dilepton
always originates from a transversely polarized photon.
