Astrophysical Tests of Modified Gravity: Stellar and Gaseous Rotation Curves in Dwarf Galaxies

TL;DR

This study uses dwarf galaxy rotation curves to test modified gravity theories, constraining model parameters and demonstrating the potential of astrophysical observations to probe new regions of parameter space.

Contribution

It provides new astrophysical constraints on chameleon and $f(R)$ gravity theories using stellar and gaseous rotation curves of dwarf galaxies.

Findings

Ruled out $f_{R0}>10^{-6}$ for $f(R)$ theories.

Constrained self-screening parameters $ ext{chi}_c>10^{-6}$ for fifth-force strengths as low as 0.05.

Astrophysical bounds can access previously unexplored parameter regions.

Abstract

Chameleon theories of gravity predict that the gaseous component of isolated dwarf galaxies rotates with a faster velocity than the stellar component. In this paper, we exploit this effect to obtain new constraints on the model parameters using the measured rotation curves of six low surface brightness galaxies. For $f(R)$ theories, we rule out values of $f_{R0}>10^{-6}$. For more general theories, we find that the constraints from Cepheid variable stars are currently more competitive than the bounds we obtain here but we are able to rule out self-screening parameters $\chi_c>10^{-6}$ for fifth-force strengths (coupling of the scalar to matter) as low as $0.05$ the Newtonian force. This region of parameter space has hitherto been inaccessible to astrophysical probes. We discuss the future prospects for improving these bounds.