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Shear viscosities from Kubo formalism in a large-N_c Nambu & Jona-Lasinio model

Robert Lang,
Norbert Kaiser,
Wolfram Weise
In this work the shear viscosity of strongly interacting matter is calculated within a two-flavor Nambu--Jona-Lasinio model as a function of temperature and chemical potential. The general Kubo formula is applied, incorporating the full Dirac structure of the thermal quark spectral function and avoiding commonly used on-shell approximations. Mesonic fluctuations contributing via Fock diagrams provide the dominant dissipative processes. The resulting ratio η/s (shear viscosity over entropy density) decreases with temperature and chemical potential. In combination with hard-thermal-loop results a minimum slightly above the AdS/CFT benchmark η/s=1/4π is obtained.
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Eur. Phys. J. A51 (2015) 127
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