Shear flows in far-from-equilibrium strongly coupled fluids

Abstract

Despite the viscosity of a fluid ranges over several order of magnitudes and is extremely sensitive to microscopic structure and molecular interactions, it has been conjectured that its minimum displays a universal value which is experimentally approached in strongly coupled fluids such as the quarkgluon plasma. Recent early-time analysis suggests that hydrodynamics could serve as a universal attractor even when the deformation gradients are large and that dissipative transport coefficients, such as viscosity, could still display a universal behavior far-from-equilibrium. Motivated by these observations, we consider the real-time dissipative dynamics of two different bottom-up conformal holographic models under large shear deformations. We compute the viscosity-to-entropy density ratio in several states driven away from equilibrium by large time dependent shear rates. In all the cases considered, we observe that, in the late-time far-from-equilibrium state, both the viscosityentropy ratio and the dimensionless ratio between energy density and entropy density approach a universal value which is completely independent of the initial conditions, the form of the driving and the parameters of the system. Moreover, the late-time universal value coincides with the expectation from hydrodynamics naively valid only near equilibrium.

Thermoelectric Transport in Holographic Quantum Matter under Shear Strain

“…Nevertheless, nonlinear elastic response can be obtained using holographic methods, yielding a rich phenomenology of nonlinear elasticity behaviours, see e.g. [22][23][24][25]. Given the full stress-strain curves, one can define the nonlinear elastic shear modulus G ≡ dΣ/dε.…”

“…The thermodynamic and mechanical properties of a holographic bottom-up model for the supersolid were considered in [23]. Interestingly, shear flows in some holographic models were investigated in [24] where the viscosity-entropy density ratio shows some universality even far away from equilibrium. 1 For a strongly coupled system at finite temperature, T , and charge density, ρ, its response to the application of an electric field E i and a temperature gradient ∂ i T is char-acterized by the thermoelectric transport coefficients in linear response:…”