On the violation of the holographic viscosity versus entropy KSS bound in non relativistic systems

TL;DR

This paper investigates violations of the holographic viscosity-entropy bound in non-relativistic systems using field theory models, suggesting particle production and molecular complexity could challenge the bound's validity.

Contribution

It demonstrates how increasing particle degeneracy and molecular isomers can violate the KSS bound in non-relativistic regimes, providing theoretical insights and potential experimental implications.

Findings

KSS bound can be exceeded by increasing degenerate pions

Large molecular isomers may violate the bound in strong sense

Heavy Ion Collisions could set upper limits on hadron resonances

Abstract

A computation of the quotient of shear viscosity to entropy density, or KSS number $\eta/s$ is performed, in the non-relativistic and classical regime, first in Chiral Perturbation Theory, and then in the $SO(g+1)/SO(g)$ Non-Linear Sigma Model in the large $g$ limit. Both are field theories stemming from a renormalizable Sigma Model but in spite of that, we explicitly calculate how one undercomes the KSS bound by increasing the number of degenerate pions sufficiently. However we argue that particle production could still keep the validity of the KSS bound in the weak sense. We also show how a large number of molecular isomers (that we estimate in terms of simple molecular properties) could undercome the bound in the strong sense. This might be possible with carbon-based molecules. We finally argue that a measurement of $\eta/s$ in Heavy Ion Collisions might be turned into an upper bound on the number of hadron resonances.