$k$-evolution: a relativistic N-body code for clustering dark energy

TL;DR

The paper presents $k$-evolution, a relativistic N-body simulation code incorporating clustering dark energy using effective field theory, enabling detailed study of dark energy effects on cosmic structure formation.

Contribution

It introduces a new relativistic N-body code that models clustering dark energy with a focus on $k$-essence, extending previous tools to include dark energy non-linearities.

Findings

Dark energy clustering impacts matter power spectrum

Relativistic effects influence gravitational potential evolution

Dark energy affects massive halo formation

Abstract

We introduce $k$-evolution, a relativistic $N$-body code based on $\textit{gevolution}$, which includes clustering dark energy among its cosmological components. To describe dark energy, we use the effective field theory approach. In particular, we focus on $k$-essence with a speed of sound much smaller than unity but we lay down the basis to extend the code to other dark energy and modified gravity models. We develop the formalism including dark energy non-linearities but, as a first step, we implement the equations in the code after dropping non-linear self-coupling in the $k$-essence field. In this simplified setup, we compare $k$-evolution simulations with those of $\texttt{CLASS}$ and $\textit{gevolution}$ 1.2, showing the effect of dark matter and gravitational non-linearities on the power spectrum of dark matter, of dark energy and of the gravitational potential. Moreover, we compare $k$-evolution to Newtonian $N$-body simulations with back-scaled initial conditions and study how dark energy clustering affects massive halos.