Collective interaction of mesons in hot hadronic matter

We calculate momentum-dependent optical potentials (both real and imaginary parts) for mesons propagating in hot hadronic matter. For sufficiently dilute matter the results obtained are essentially model-independent, and based directly on experimental information about hadronic scattering amplitudes. Even at the lowest (break-up) temperatures available in high-energy hadronic collisions, T_f = 120-150 MeV, these potentials can significantly modify spectra of the outgoing hadron, leading to a peak at small p_t. Other observable consequences of these phenomena are changes of the line shape of ρ{variant}-, ω- and φ-mesons, which can be observed in the dilepton mode. For such mesons, decaying inside the matter, we estimate both the expected shift and broadening of the peaks.