SELCIE: A tool for investigating the chameleon field of arbitrary sources

TL;DR

SELCIE is a software tool that numerically solves the nonlinear chameleon field equations for arbitrary mass distributions, enabling detailed investigations of modified gravity models with strong agreement to existing analytic solutions.

Contribution

The paper introduces SELCIE, a novel software package that uses finite element methods to solve the chameleon field equations for arbitrary sources, extending beyond symmetric systems.

Findings

SELCIE achieves sub-percentage accuracy compared to analytic solutions.

The tool effectively handles complex, arbitrary mass distributions.

It facilitates detailed studies of chameleon gravity models.

Abstract

The chameleon model is a modified gravity theory that introduces an additional scalar field that couples to matter through a conformal coupling. This `chameleon field' possesses a screening mechanism through a nonlinear self-interaction term which allows the field to affect cosmological observables in diffuse environments whilst still being consistent with current local experimental constraints. Due to the self-interaction term the equations of motion of the field are nonlinear and therefore difficult to solve analytically. The analytic solutions that do exist in the literature are either approximate solutions and or only apply to highly symmetric systems. In this work we introduce the software package SELCIE (https://github.com/C-Briddon/SELCIE.git). This package equips the user with tools to construct an arbitrary system of mass distributions and then to calculate the corresponding solution to the chameleon field equation. It accomplishes this by using the finite element method and either the Picard or Newton nonlinear solving methods. We compared the results produced by SELCIE with analytic results from the literature including discrete and continuous density distributions. We found strong (sub-percentage) agreement between the solutions calculated by SELCIE and the analytic solutions.