EXACT INFRARED BEHAVIOR OF SUPERFLUID INTERACTING BOSONS AT ZERO-TEMPERATURE

The superfluid character of an interacting Bose-condensed system is re lated to the infrared behavior of the quasiparticle spectrum. We explo it the symmetries associated with the superfluid stable phase to deal with the infrared divergences and obtain the exact infrared behavior o f the system at zero temperature. For spatial dimension d greater than three we find that the Bogoliubov solution is exact, while for 1 < d less than or equal to 3 a new fixed point controls the infrared behavi or of the system leading to a singular lungitudinal Green's function. In both cases phonons constitute the elementary excitations of the sys tem.