Three-body force effect on off-shell mass operator and spectral functions in nuclear matter

Within the framework of the Brueckner theory, the off-shell behaviors of the mass operator M(k, omega) = V (k, omega) + iW(k, omega), i.e., its dependence upon the momentum k and upon the nucleon frequency omega, are investigated by including nuclear three-body force (TBF). The first two terms of the hole-line expansion of the mass operator are taken into account. The TBF effects on their off-shell properties are discussed. A comparison is made between the on-shell and off-shell values of M-1. The nucleon spectral function and nucleon momentum distribution are also calculated, and the calculation shows that they are hardly affected by the TBF effect at the saturation density. At a density two times greater than the saturation density, inclusion of the TBF may lead to a visible effect on the spectral function and may enhance the depletion of the hole states.