Model of Dark Matter and Dark Energy Based on Gravitational Polarization

TL;DR

This paper introduces a gravitational polarization model for dark matter and dark energy, showing it aligns with Lambda-CDM cosmology and reproduces MOND phenomenology at galactic scales, with a natural cosmological constant.

Contribution

It proposes a dipolar medium model within general relativity that unifies dark matter and dark energy and explains galactic dynamics without new particles.

Findings

Dipolar fluid mimics Lambda-CDM at cosmological scales.

Model reproduces MOND phenomenology at galactic scales.

Cosmological constant naturally arises from the model.

Abstract

A model of dark matter and dark energy based on the concept of gravitational polarization is investigated. We propose an action in standard general relativity for describing, at some effective or phenomenological level, the dynamics of a dipolar medium, i.e. one endowed with a dipole moment vector, and polarizable in a gravitational field. Using first-order cosmological perturbations, we show that the dipolar fluid is undistinguishable from standard dark energy (a cosmological constant Lambda) plus standard dark matter (a pressureless perfect fluid), and therefore benefits from the successes of the Lambda-CDM (Lambda-cold dark matter) scenario at cosmological scales. Invoking an argument of "weak clusterisation" of the mass distribution of dipole moments, we find that the dipolar dark matter reproduces the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. The dipolar medium action naturally contains a cosmological constant, and we show that if the model is to come from some fundamental underlying physics, the cosmological constant Lambda should be of the order of a0^2/c^4, where a0 denotes the MOND constant acceleration scale, in good agreement with observations.