Equation of state of an interacting pion gas with realistic π-π interactions

Within the finite-temperature Green close-quote s-function formalism we study the equation of state of a hot interacting pion gas at zero chemical potential. Employing realistic ππ meson-exchange interactions, we self-consistently calculate the in-medium single-pion self-energy and the ππ scattering amplitude in the quasiparticle approximation. These quantities are then used to evaluate the thermodynamic potential Ωπ(T) from which the state variables of pressure, entropy, and energy density can be derived. In contrast to earlier calculations based on the low-energy Weinberg Lagrangian we find an overall increase as compared to the free-gas results. We also consider the possibility of a dropping ρ-meson mass as suggested by the open-quote open-quote Brown-Rho scaling close-quote close-quote law. copyright 1996 The American Physical Society