Shear viscosity of pion gas due to $\rho \pi \pi$ and $\sigma \pi \pi$ interactions

Abstract

We have evaluated the shear viscosity of pion gas taking into account its scattering with the low mass resonances, $\sigma$ and $\rho$ during propagation in the medium. The thermal width (or collisional rate) of the pions is calculated from $\pi \sigma$ and $\pi \rho$ loop diagrams using effective interactions in the real time formulation of finite temperature field theory. A very small value of shear viscosity by entropy density ratio ($\eta /s$), close to the KSS bound, is obtained which approximately matches the range of values of $\eta /s$ used by Niemi et al. \cite{Niemi} in order to fit the RHIC data of elliptic flow.

Comments: 7 pages, 8 figures