The Effective Field Theory of Cosmological Large Scale Structures

TL;DR

This paper develops an effective field theory for large scale structures in cosmology, enabling precise predictions of matter distribution by incorporating UV physics effects into an IR effective fluid model.

Contribution

It introduces an effective fluid approach with parameters derived from UV physics, improving the accuracy of large scale structure predictions over standard perturbation theory.

Findings

Effective fluid parameters measured from simulations.

Perturbative expansion converges for all relevant scales.

Predictions match observations with percent accuracy up to k ~ 0.24 h/Mpc.

Abstract

Large scale structure surveys will likely become the next leading cosmological probe. In our universe, matter perturbations are large on short distances and small at long scales, i.e. strongly coupled in the UV and weakly coupled in the IR. To make precise analytical predictions on large scales, we develop an effective field theory formulated in terms of an IR effective fluid characterized by several parameters, such as speed of sound and viscosity. These parameters, determined by the UV physics described by the Boltzmann equation, are measured from N-body simulations. We find that the speed of sound of the effective fluid is c_s^2 10^(-6) and that the viscosity contributions are of the same order. The fluid describes all the relevant physics at long scales k and permits a manifestly convergent perturbative expansion in the size of the matter perturbations \delta(k) for all the observables. As an example, we calculate the correction to the power spectrum at order \delta(k)^4. The predictions of the effective field theory are found to be in much better agreement with observation than standard cosmological perturbation theory, already reaching percent precision at this order up to a relatively short scale k \sim 0.24 h/Mpc.