Testing Modified Gravity Theories with Numerical Solutions of the External Field Effect in Rotationally Supported Galaxies

TL;DR

This paper compares two modified gravity theories, AQUAL and QUMOND, by analyzing their external field effects in galaxies, finding AQUAL aligns better with cosmic observations and may be a more viable theory.

Contribution

The study provides numerical solutions of the external field effect in AQUAL and QUMOND, and compares their predictions with cosmic baryon distribution to evaluate their validity.

Findings

AQUAL's external field strength matches cosmic estimates

QUMOND's external field strength is somewhat higher

AQUAL is likely a better effective non-relativistic limit

Abstract

The strong equivalence principle is violated by gravity theories of Milgromian dynamics (MOND) through the action of the external field effect. We test two different Lagrangian theories AQUAL and QUMOND based on their numerical solutions of the external field effect, by comparing two independent estimates of the mean external field strength of the nearby universe: a theory-deduced value from fitting the outer rotation curves of 114 galaxies and an empirical value from the large-scale distribution of cosmic baryons. The AQUAL-deduced external field strength from rotation curves agrees with that from the large-scale cosmic environment, while QUMOND-deduced value is somewhat higher. This suggests that AQUAL is likely to be preferred over QUMOND as an effective non-relativistic limit of a potential relativistic modified gravity theory.