The ratio of viscosity to entropy density in a pion gas satisfies the   KSS holographic bound
  We evaluate the ratio of shear viscosity to entropy density in a pion gas employing the Uehling-Uehlenbeck equation and experimental phase-shifts parameterized by means of the SU(2) Inverse Amplitude Method. We find that the ratio for this monocomponent gas stays well above the KSS 1/(4 pi) bound. We find similar results with other sets of phase shifts and conclude the bound is nowhere violated. 
Antonio Dobado and Felipe J. Llanes-Estrada (U. Complutense Madrid)