Rho Meson Broadening in Hot and Dense Hadronic Matter

The modification of the width of rho mesons due to in-medium decays and collisions is evaluated. The decay width is calculated from the imaginary part of the one-loop self-energy at finite temperature. The collision width is related to the cross sections of the $\rho$ + pion and the $\rho$ + nucleon reactions. A calculation based on an effective Lagrangian shows the importance of including the direct $\rho\pi\to\rho\pi$ scattering which is dominated by the $a_1$ exchange. A large broadening of the spectral function is found, accompanied by a strength suppression at the pole.