Structure Formation in Nonlocal MOND

TL;DR

This paper investigates structure formation within a nonlocal MOND framework, deriving linear perturbation equations and highlighting challenges in matter-driven structure growth, suggesting potential model modifications.

Contribution

It provides the first derivation of linear scalar perturbation equations in a nonlocal MOND model and analyzes their implications for structure formation.

Findings

MOND enhancement insufficient for matter-driven structure formation

Simplified equations for sub-horizon modes

Discussion of potential model modifications

Abstract

We consider structure formation in a nonlocal, metric-based realization of Milgrom's MOdified Newtonian Dynamics (MOND). We derive the general equations for linearized scalar perturbations about the $\Lambda$CDM expansion history. These equations are considerably simplified for sub-horizon modes, and it becomes obvious (in this model) that the MOND enhancement is not sufficient to allow ordinary matter to drive structure formation. We discuss ways in which the model might be changed to correct the problem.