Dipolar Dark Matter and Cosmology

TL;DR

This paper reviews a relativistic dipolar dark matter model that mimics MOND phenomenology and explores its cosmological implications, including modifications to curvature perturbations and non-Gaussianities constrained by Planck data.

Contribution

It introduces a relativistic dipolar dark matter model within general relativity that aligns with Lambda-CDM at first order and predicts unique second-order effects.

Findings

Model reproduces MOND phenomenology via gravitational polarization.

At second order, dipolar dark matter induces non-Gaussianities in the curvature bispectrum.

Planck data constrains the primordial dipole field value.

Abstract

The phenomenology of the modified Newtonian dynamics (MOND) can be recovered from a mechanism of "gravitational polarization" of some dipolar medium playing the role of dark matter. We review a relativistic model of dipolar dark matter (DDM) within standard general relativity to describe, at some effective level, a fluid polarizable in a gravitational field. At first order in cosmological perturbation theory, this model is equivalent to the concordance cosmological scenario, or Lambda-cold dark matter (CDM) model. At second order, however, the internal energy of DDM modifies the curvature perturbation generated by CDM. This correction, which depends quadratically on the dipole, induces a new type of non-Gaussianity in the bispectrum of the curvature perturbation with respect to standard CDM. Recent observations by the Planck satellite impose stringent constraints on the primordial value of the dipole field.