Releasing scalar fields: cosmological simulations of scalar-tensor theories for gravity beyond the static approximation

TL;DR

This paper introduces a new method for cosmological simulations that solves the full equations of motion for scalar fields, revealing significant differences from the quasi-static approximation and uncovering new physical phenomena.

Contribution

It presents a novel simulation approach that models the full dynamics of scalar fields in cosmology, surpassing the traditional quasi-static approximation.

Findings

Significant differences between full and quasi-static scalar field evolution.

Revealed new physical properties of scalar fields.

Uncovered astrophysical phenomena previously hidden in simulations.

Abstract

Several extensions of General Relativity and high energy physics include scalar fields as extra degrees of freedom. In the search for predictions in the non-linear regime of cosmological evolution, the community makes use of numerical simulations in which the quasi-static limit is assumed when solving the equation of motion of the scalar field. In this Letter, we propose a method to solve the full equations of motion for scalar degrees of freedom coupled to matter. We run cosmological simulations which track the full time and space evolution of the scalar field, and find striking differences with respect to the commonly used quasi-static approximation. This novel procedure reveals new physical properties of the scalar field and uncovers concealed astrophysical phenomena which were hidden in the old approach.