Galactic Compton Wavelengths in $f(R)$ Screening Theories

TL;DR

This paper investigates the validity of common approximations in $f(R)$ modified gravity theories, revealing that neglecting the scalar mode mass inside galaxies can lead to significant errors in screening assessments.

Contribution

It demonstrates that the assumption of negligible scalar mode mass inside galaxies often fails, impacting the interpretation of $f(R)$ screening tests.

Findings

Neglecting scalar mass can lead to incorrect screening predictions.

The approximation may fail in observationally relevant parameter regions.

Implications for testing $f(R)$ gravity theories in astrophysical contexts.

Abstract

$f(R)$ theories of modified gravity may be compatible with current observations if the deviations from general relativity are sufficiently well screened in dense environments. In recent work [arXiv:2310.19955] we have shown that approximations commonly used to assess whether galaxies are screened, or unscreened, fail to hold in observationally interesting parts of parameter space. One of the assumptions commonly made in these approximations, and more broadly in the study of $f(R)$ models, is that the mass of the scalar mode can be neglected inside a galaxy. In this work we demonstrate that this approximation may fail spectacularly and discuss the implications of this for tests of the theory.