MOMENTUM DISTRIBUTION IN NUCLEAR-MATTER WITHIN A PERTURBATION APPROXIMATION

It is shown that the norm corrections, introduced to avoid the violati on of the constraints on the depletion of the hole states in the stand ard perturbative 2p2h approach, leads in nuclear matter to a dependenc e of the momentum distribution with the total nucleon number. This unp hysical behavior, which in turn makes the depletion to be nonextensive , arises from contributions of disconnected diagrams contained in the norm. It is found that the extensivity is again recovered when the 4p4 h excitations in the ground state are included, and a reasonable value for the total number of nucleons promoted above the Fermi level is ob tained.