Dark Energy and Modified Gravity in the Effective Field Theory of Large-Scale Structure

TL;DR

This paper presents a unified framework combining Effective Field Theory approaches to model and compute observables of dark matter clustering beyond linear scales in dark energy and modified gravity scenarios, focusing on Horndeski theories.

Contribution

It introduces a novel method integrating EFT of Dark Energy and EFT of Large-Scale Structure to analyze nonlinear clustering in modified gravity models.

Findings

Computed the one-loop dark matter power spectrum in modified gravity.

Provided a controlled expansion for mildly nonlinear scales.

Enhanced understanding of dark energy effects on structure formation.

Abstract

We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper, focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.