non-perturbative corrections of shear viscosity to entropy ratio

Shear viscosity to entropy ratio has a universal lower bound which may be violated under some effects. this paper would like to consider non-perturbative quantum corrections on the mentioned ratio in a stu black hole background. the stu model is a gravitational background that is the holographic dual of $n=4$ super yang-mills quark-gluon plasma with the chemical potential. non-perturbative corrections to the black hole entropy emerge as an exponential term which may affect the shear viscosity to entropy ratio. all possibilities will study in this paper to extract the shear viscosity of a quark-gluon plasma. we find that the universal lower bound the shear viscosity to entropy ratio may be violated due to the non-perturbative corrections.