Improving relativistic MOND with Galileon k-mouflage

TL;DR

This paper introduces a simplified covariant Galileon-based field theory that reproduces MOND phenomenology at galaxy scales, passes solar system tests, and avoids instabilities associated with higher derivatives.

Contribution

It presents a novel, simplified relativistic MOND model with an extended Vainshtein mechanism, eliminating the need for fine-tuning and vector field dynamics.

Findings

Model reproduces MOND at galaxy scales

Passes solar-system and binary pulsar tests

Avoids instabilities from higher derivatives

Abstract

We propose a simple field theory reproducing the MOND phenomenology at galaxy scale, while predicting negligible deviations from general relativity at small scales thanks to an extended Vainshtein ("k-mouflage") mechanism induced by a covariant Galileon-type Lagrangian. The model passes solar-system tests at the post-Newtonian order, including those of local Lorentz invariance, and its anomalous forces in binary-pulsar systems are orders of magnitude smaller than the tightest experimental constraints. The large-distance behavior is obtained as in Bekenstein's tensor-vector-scalar (TeVeS) model, but with several simplifications. In particular, no fine-tuned function is needed to interpolate between the MOND and Newtonian regimes, and no dynamics needs to be defined for the vector field because preferred-frame effects are negligible at small distances. The field equations depend on second (and lower) derivatives, and avoid thus the generic instabilities related to higher derivatives. Their perturbative solution around a Schwarzschild background is remarkably simple to derive. We also underline why the proposed model is particularly efficient within the class of covariant Galileons.