PION PROPAGATOR IN THE CHIRAL SIGMA-MODEL OF NUCLEAR-MATTER

Pion propagator is studied in the chiral sigma model at the zero tempe rature nuclear matter. Due to the tachyon pole of the pi and sigma tre e approximation propagators, only the nucleon polarization insertion l oop (explicitly density dependent part and vacuum fluctuation part) ca n be fully included into the pion propagator. The vacuum fluctuation a s a function of nucleon effective mass or pion external momentum (afte r Wick rotation) is negative for most of the cases. So the variation o f nucleon effective mass is restricted to a very limited region where is free of pion condensation (otherwise the nucleon energy density wil l be complex). The effect of NN short-range correlation is calculated and it is very small for low momentum.