Effective description of dark matter as a viscous fluid

TL;DR

This paper proposes modeling dark matter as a viscous fluid at large scales, enhancing the accuracy of density and velocity power spectra calculations and improving perturbation theory convergence.

Contribution

It introduces a coarse-graining approach to treat dark matter as a viscous fluid, providing a more accurate framework than the ideal pressureless fluid model.

Findings

Improved convergence of cosmological perturbation theory.

Enhanced accuracy in density and velocity power spectra calculations.

Framework applicable through a specific coarse-graining procedure.

Abstract

Treating dark matter at large scales as an effectively viscous fluid provides an improved framework for the calculation of the density and velocity power spectra compared to the standard assumption of an ideal pressureless fluid. We discuss how this framework can be made concrete through an appropriate coarse-graining procedure. We also review results that demonstrate that it improves the convergence of cosmological perturbation theory.