The phenomenological evidence for the role of quantum statistical mechanics for parton distributions has encouraged to write Fermi-Dirac expressions for the fermions and a Planck form for the gluons. The QCD equilibrium conditions for the elementary processes involved in DGLAP evolution equations allow to disentangle the contributions of the valence partons and of their antiparticles and give successful predictions for the isospin and spin asymmetries of the sea.
The resulting parametrization has a better predictive power in the regions, where the experimental knowledge is scarce, than the standard polynomial ones.
