  T-odd parton distribution functions in a Drell-Yan process are here studied
by examining the evolution of the internal statistical properties of the
interacting hadrons. T-odd functions are shown to be a signature of the
irreversible process in which a hadronic state characterized by long range
correlation properties (hadronic phase) decays to produce a cloud of
independent partons (partonic phase) because of initial/final state
interactions. The relevant considered variable is the rate of increase of the
entropy of the hadronic system. This quantity is shown to be roughly equal to
the decay rate of the hadronic state. Conditions for getting a leading twist
T-odd effect are established on this basis. Last, the relevant case of a large
entropy increase associated with transverse-dominated initial/final state
interactions is analyzed.
