Viscous conformal gauge theories

We present the conformal behavior of the shear viscosity-to-entropy density ratio and the fermion-number diffusion coefficient within the perturbative regime of the conformal window for gauge-fermion theories.

Figure 1

Left panel: $\eta /s$ evaluated at the IR fixed point, as a function of the number of flavors, for fermions in the fundamental representation with $N=3$ colors. Right panel: $\eta /s$ as a function of the temperature over the Renormalization Group (RG) scale $\mathrm{\Lambda }$ for different values of $N_f$ in the conformal window and one outside corresponding to $N_f=6$, for $N=3$ colors. Although $N_f=14$ still displays a potential IR fixed point the IR dynamics of $\eta /s$ cannot be accessed perturbatively. The horizontal line at the bottom is the conjectured AdS/CFT bound.

Figure 2

Left panel: $(TD{)}^{\mathrm{IR}}$ as a function of the number of flavors, for the case of fermions in the fundamental representation and $N=3$. Right panel: $TD$ as a function of the temperature, for different values of $N_f$ and $N=3$.