Shear viscosity and phase diagram from Polyakov–Nambu–Jona-Lasinio model

We present a detailed study of the variation of shear viscosity $\eta$, with temperature and baryon chemical potential within the framework of the Polyakov–Nambu–Jona-Lasinio model. $\eta$ is found to depend strongly on the spectral width of the quasiparticles present in the model. The variation of $\eta$ across the phase diagram has distinctive features for different kinds of transitions. These variations have been used to study the possible location of the critical end point and are cross-checked with similar studies of variations of specific heat. Finally, using a parametrization of the freeze-out surface in heavy-ion collision experiments, the variation of the shear viscosity to entropy density ratio has also been discussed as a function of the center-of-mass energy of collisions.

Figure 1

$\eta$ as a function of temperature at the vanishing chemical potential for different forms of $\mathrm{\Gamma }$.

Figure 2

$\eta$ as a function of the quark chemical potential at fixed temperatures for different forms of $\mathrm{\Gamma }$.

Figure 3

Variation of shear viscosity with the quark chemical potential at different temperatures.

Figure 4

Specific shear viscosity ($\frac{\eta }{s}$) as a function of temperature at the vanishing chemical potential.

Figure 5

$\frac{\eta }{s}$ as a function of temperature for different nonzero values of the quark chemical potential.

Figure 6

Phase diagram for the $2+1$-flavor PNJL model.

Figure 7

$C_V/T^3$ as a function of temperature for different values of ${\mu }_q$.

Figure 8

$\frac{\eta }{s}$ under different center-of-mass energies at freeze-out.