# Brief History of Ultra-light Scalar Dark Matter Models

## TL;DR

This review traces the development of ultra-light scalar dark matter models, highlighting their wave-like behavior, formation as Bose-Einstein condensates, and potential to resolve small-scale structure issues in cosmology.

## Contribution

It provides a comprehensive overview of the history, theoretical foundations, and implications of ultra-light scalar dark matter models, emphasizing their unique quantum and astrophysical properties.

## Key findings

- Scalar dark matter behaves as a classical wave at galactic scales.
- Quantum pressure suppresses small-scale structure formation.
- Models can address the small-scale crisis of cold dark matter.

## Abstract

This is a review on the brief history of the scalar field dark matter model also known as fuzzy dark matter, BEC dark matter, wave dark matter, or ultra-light axion. In this model ultra-light scalar dark matter particles with mass $m = O(10^{-22})eV$ condense in a single Bose-Einstein condensate state and behave collectively like a classical wave. Galactic dark matter halos can be described as a self-gravitating coherent scalar field configuration called boson stars. At the scale larger than galaxies the dark matter acts like cold dark matter, while below the scale quantum pressure from the uncertainty principle suppresses the smaller structure formation so that it can resolve the small scale crisis of the conventional cold dark matter model.