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Updated: Oct 19, 2025

Studying Large Amplitude Oscillatory Shear Response of Soft Materials
Published on: April 25, 2019
Shear Viscosity at Infinite Coupling: A Field Theory Calculation
1Department of Physics, University of Colorado, Boulder, Colorado 80309, USA and Center for Theory of Quantum Matter, University of Colorado, Boulder, Colorado 80309, USA.
Abstract:
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 coupling result for the viscosity is universal for a large class of interacting bosonic O(N) models.
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