Shear viscosity of a pion gas due to $ρππ$ and $σππ$ interactions
We have calculated the shear viscosity of pion medium, where propagating pion has some finite thermal width due to interaction with the low mass resonances, $σ$ and $ρ$. With the help of standard thermal field theoretical technique, the thermal width of the pion has been calculated from the pion self-energy diagram for $πσ$ and $πρ$ loops, where an effective Lagrangian density has been used for interaction part. We have found a very small value of shear viscosity by entropy density ratio ($η/s$), which is very close to the KSS bound.
nucl-th↗