MOND and its bimetric formulation

TL;DR

This paper reviews MOND, emphasizing scale invariance, and explores a bimetric relativistic formulation (BIMOND), highlighting its limits, cosmological implications, and potential to address gravitational phenomena without dark matter.

Contribution

It provides a detailed analysis of BIMOND, a relativistic MOND theory, including its limits, cosmological aspects, and its promising features compared to other theories.

Findings

BIMOND reduces to GR when a0 approaches zero.

It correctly describes gravitational lensing.

BIMOND naturally incorporates a cosmological constant of observed order.

Abstract

I first give a succinct account of the MOND paradigm--emphasizing the centrality of scale invariance in the nonrelativistic, deep-MOND limit--and describing rudiments of its phenomenology. I then present my credo, and some generalities, concerning existing MOND theories. Then I concentrate on one relativistic formulation of MOND in the form of a bimetric theory (BIMOND). I describe its various limits: the weak field, with application to gravitational waves, the nonrelativistic limit, and their further deep-MOND (low acceleration) limits, which are scale invariant. Other aspects of BIMOND that have been explored are aspects of cosmology, matter fluctuations in cosmology, and matter-twin-matter interactions. BIMOND remains largely unexplored, despite its promise in several regards: It tends to GR for a0 goes to 0 (a0 is the MOND constant); it has a simple nonrelativistic limit; it describes gravitational lensing correctly; and, it has a generic appearance of a cosmological-constant term that is of order a0^2/c^4, as observed.