# Reconstructing Horndeski models from the effective field theory of dark energy

## TL;DR

This paper presents a method to reconstruct covariant Horndeski scalar-tensor theories from the effective field theory of dark energy, enabling better interpretation of cosmological constraints in fundamental models.

## Contribution

It introduces a reconstruction technique linking EFT parameters to covariant Horndeski theories, facilitating interpretation of observational constraints.

## Key findings

- Reconstructed Horndeski models matching EFT background and perturbations.
- Applied method to well-known dark energy models.
- Discussed potential applications for future cosmological analyses.

## Abstract

Studying the effects of dark energy and modified gravity on cosmological scales has led to a great number of physical models being developed. The effective field theory (EFT) of cosmic acceleration allows an efficient exploration of this large model space, usually carried out on a phenomenological basis. However, constraints on such parametrized EFT coefficients cannot be trivially connected to fundamental covariant theories. In this paper we reconstruct the class of covariant Horndeski scalar-tensor theories that reproduce the same background dynamics and linear perturbations as a given EFT action. One can use this reconstruction to interpret constraints on parametrized EFT coefficients in terms of viable covariant Horndeski theories. We demonstrate this method with a number of well-known models and discuss a range of future applications.