rho^0 mass in a hot hadron gas
  We study the behavior of the rho^0 vector mass during the hadronic phase of an ultra-relativistic heavy-ion collision at finite temperature. We show that scattering with the most abundant particles during this stage, namely, pions, kaons and nucleons, leads to an overall temperature dependent, decrease of the rho^0 intrinsic mass at rest, compared to its value in vacuum. The main contributions arise from s-channel scattering with pions through the formation of a_1 resonances as well as with nucleons through the formation of even parity, spin 3/2 [N(1720)] and 5/2 [$\Delta$(1905)] nucleon resonances. We show that it is possible to achieve a shift in the intrinsic rho^0 mass of order - 40 MeV, when including the contributions of all the relevant mesons and baryons that take part in the scattering, for temperatures between chemical and kinetic freeze-out. 
Alejandro Ayala (ICN-UNAM)