Is dark matter a BEC or scalar field?

TL;DR

This paper reviews the concept of ultra-light scalar dark matter forming Bose-Einstein condensates or boson stars, which could explain galactic dark matter properties and address issues in the standard cosmological model.

Contribution

It summarizes the history and potential of scalar field and BEC models for dark matter, highlighting their ability to reproduce galaxy rotation curves and solve small-scale structure problems.

Findings

Scalar dark matter can form BECs or boson stars.

Quantum effects suppress small-scale structure formation.

Model reproduces observed galaxy rotation curves.

Abstract

This is a brief review on the history of the Bose-Einstein condensate (BEC) or boson star model of galactic dark matter halos, where ultra-light scalar dark matter particles condense in a single BEC quantum state. The halos can be described as a self-gravitating, possibly self-interacting, coherent scalar field. On a scale larger than galaxies, dark matter behaves like cold dark matter while below that scale the quantum mechanical nature suppresses the dark matter structure formation due to the minimum length scale determined by the mass $m\st{>}{\sim}10^{-24} eV$ and the self-interaction of the particles. This property could alleviate the cusp problem and missing satellite problems of the $\Lambda$CDM model. Furthermore, this model well reproduces the observed rotation curves of spiral and dwarf galaxies, which makes the model promising.