https://doi.org/10.1140/epja/i2012-12109-3
Regular Article - Theoretical Physics
Shear viscosity of a hot pion gas
Physik Department, Technische Universität München, D-85747, Garching, Germany
* e-mail: robert.lang@ph.tum.de
Received:
30
May
2012
Revised:
16
July
2012
Accepted:
5
August
2012
Published online:
23
August
2012
The shear viscosity of an interacting pion gas is studied using the Kubo formalism as a microscopic description of thermal systems close to global equilibrium. We implement the skeleton expansion in order to approximate the retarded correlator of the viscous part of the energy-momentum tensor. After exploring this in gφ 4 theory we show how the skeleton expansion can be consistently applied to pions in chiral perturbation theory. The shear viscosity η is determined by the spectral width, or equivalently, the mean free path of pions in the heat bath. We derive a new analytical result for the mean free path which is well conditioned for numerical evaluation and discuss the temperature and pion-mass dependence of the mean free path and the shear viscosity. The ratio η/s of the interacting pion gas exceeds the lower bound 1/4π from AdS/CFT correspondence.
© SIF, Springer-Verlag Berlin Heidelberg, 2012
