Nucleon-nucleon correlation and two-pion-exchange three-body force in nuclear matter

The contribution of the two-pion-exchange three-body force to the binding energy of nuclear matter is examined, and cutoffs between all the pairs of nucle´ons are introduced. The cutoffs are meant to simulate the nucle´on-nucle´on correlation at short distances, and also separate the effect of the better known long-range part of the force from that of the unknown short-range part. The contribution is found to be much reduced compared with that obtained in a recent paper by Bhaduri, Nogami and Ross. With reasonable cutoffs and pionic form factor the contribution is found to be of the order of 2 MeV attraction per particle. The similar ΛNN three-body force is also discussed, and a serious difficulty concerning the binding mechanism of a Λ-particle in nuclear matter is pointed out.