Non-equilibrium spacetime thermodynamics, entanglement viscosity and KSS bound

Goffredo Chirco

In the framework of spacetime thermodynamics, the equations of motion for gravity can be locally derived as equations of state for a thermal Rindler wedge system at equilibrium. Moving to non-equilibrium regimes, dissipative components arise, with relation to non-local heat fluxes associated with the purely gravitational/internal degrees of freedom of the theory. These dissipative terms can be characterized by the viscosity coefficients of the membrane dynamics for the Rindler horizon. In this context, I will show how the shear viscosity to entropy density ratio associated with a Rindler horizon naturally fulfills the universal Kovtun-Son-Starinets bound and propose a microscopic explanation for the spacetime viscosity in terms of the peculiar properties of quantum entanglement and vacuum fluctuations in the Rindler wedge.