Euclid preparation. Simulations and nonlinearities beyond $\Lambda$CDM. 1. Numerical methods and validation

TL;DR

This paper reviews numerical methods and simulation codes for modeling nonlinear structure formation in theories beyond $\Lambda$CDM$, emphasizing validation and recent advances crucial for Euclid's observational goals.

Contribution

It provides a comprehensive overview of numerical techniques and a code comparison to validate simulations of alternative dark energy and modified gravity models.

Findings

High agreement among different simulation codes.

Validated methods for nonlinear regime modeling.

Enhanced simulation techniques for Euclid data analysis.

Abstract

To constrain models beyond $\Lambda$CDM, the development of the Euclid analysis pipeline requires simulations that capture the nonlinear phenomenology of such models. We present an overview of numerical methods and $N$-body simulation codes developed to study the nonlinear regime of structure formation in alternative dark energy and modified gravity theories. We review a variety of numerical techniques and approximations employed in cosmological $N$-body simulations to model the complex phenomenology of scenarios beyond $\Lambda$CDM. This includes discussions on solving nonlinear field equations, accounting for fifth forces, and implementing screening mechanisms. Furthermore, we conduct a code comparison exercise to assess the reliability and convergence of different simulation codes across a range of models. Our analysis demonstrates a high degree of agreement among the outputs of different simulation codes, providing confidence in current numerical methods for modelling cosmic structure formation beyond $\Lambda$CDM. We highlight recent advances made in simulating the nonlinear scales of structure formation, which are essential for leveraging the full scientific potential of the forthcoming observational data from the Euclid mission.