# Shear Viscosity at Infinite Coupling: A Field Theory Calculation.

@article{Romatschke2021ShearVA,
title={Shear Viscosity at Infinite Coupling: A Field Theory Calculation.},
author={Paul Romatschke},
journal={Physical review letters},
year={2021},
volume={127 11},
pages={
111603
}
}
• P. Romatschke
• Published 13 April 2021
• Physics
• Physical review letters
I derive an exact integral expression for the ratio of shear viscosity over entropy density η/s for the massless (critical) O(N) model at large N with quartic interactions. The calculation is set up and performed entirely from the field theory side using a nonperturbative resummation scheme that captures all contributions to leading order in large N. In 2+1d, η/s is evaluated numerically at all values of the coupling. For infinite coupling, I find (η/s)≃0.42(1)×N. I show that this strong…
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