Shear viscosity to entropy density ratio: A powerful tool for gravity theories and strongly coupled fluids
General Relativity and Quantum Cosmology
2025-09-09 v1 Quantum Gases
High Energy Physics - Theory
Abstract
In this perspective review, we present a concise yet multifaceted overview of the pivotal role played by the the shear viscosity to entropy density ratio across various physical contexts. After summarizing some of the main aspects of the bound obtained by Kovtun, Son and Starinets, we examine potential sources of its violation, exploring the insights these may offer and their connections to fundamental causality conditions. We also review a range of experimental tests conducted in diverse, yet complementary, physical systems, discussing the prospects opened by upcoming measurements.
Keywords
Cite
@article{arxiv.2509.06178,
title = {Shear viscosity to entropy density ratio: A powerful tool for gravity theories and strongly coupled fluids},
author = {Marilù Chiofalo and Dario Grasso and Stefano Liberati and Massimo Mannarelli},
journal= {arXiv preprint arXiv:2509.06178},
year = {2025}
}