A semi-analytic estimate for the effective sound speed counterterm in the EFTofLSS

TL;DR

This paper introduces a semi-analytic method to estimate the effective sound speed in the EFTofLSS, linking nonlinear power spectra to the parameter and exploring its cosmology dependence.

Contribution

The work provides a novel semi-analytic approach to estimate the EFTofLSS sound speed using the Layzer-Irvine equation and separate universe techniques, aligning well with simulations.

Findings

Estimate of the sound speed agrees with simulations within tens of percent.

The method reveals how the sound speed depends on cosmological parameters.

The approach offers a new way to connect nonlinear spectra to EFT parameters.

Abstract

The Effective Field Theory of Large Scale Structure (EFTofLSS) has found tremendous success as a perturbative framework for the evolution of large scale structure, and it is now routinely used to compare theoretical predictions against cosmological observations. The model for the total matter field includes one nuisance parameter at 1-loop order, the effective sound speed, which can be extracted by matching the EFT to full N-body simulations. In this work we first leverage the Layzer-Irvine cosmic energy equation to show that the equation of state can be exactly computed with knowledge of the fully nonlinear power spectrum. When augmented with separate universe methods, we show one can estimate the effective sound speed. This estimate is in good agreement with simulation results, with errors at the few tens of percent level. We apply our method to investigate the cosmology dependence of the effective sound speed and to shed light on what cosmic structures shape its value.