Modifications of the rho-meson from the virtual pion cloud in hot and dense matter

Abstract

The modification of the ρ-meson self-energy due to the coupling to in-medium pions is calculated consistently at finite baryon density and temperature, keeping the full 3-momentum dependence in a gauge invariant way. As a function of nucleon density, the ρ-meson spectral function is strongly enhanced in the invariant mass region M≲650 MeV , while the maximum, i.e., the pole mass, is slightly shifted upwards. As a function of temperature, for fixed nucleon density, the imaginary part of the self-energy increases further due to Bose-enhancement. At the same time the mass shift from the real part becomes very large. As a consequence of these medium effects, the dilepton rate in the low-mass region M≲650 MeV increases strongly, while the peak at M≈770 MeV disappears.