Kinetic properties of a pion gas

Zubarev's nonequilibrium statistical operator method is used to obtain kinetic equations for certain models of the interaction of a neutral $\pi$-meson gas. On the basis of their solution in the relaxation time approximation, the transport coefficients are found, and these are investigated in the region of relativistic temperatures. It is shown that the well-known result $\eta\sim T^3$ for the viscosity obtained by Iso, Mort, and Namiki corresponds to the model $\mathfrak g\varphi^4$. It is shown that the transport coefficients in renormalizable models increase with increasing temperature, and decrease in nonrenormaltzable models.