Free streaming of warm wave dark matter in modified expansion histories

TL;DR

This paper investigates how the free streaming of ultra-light wave dark matter is influenced by different cosmological expansion histories, using Lyman-alpha forest data to constrain model parameters and explore implications for structure formation.

Contribution

It introduces a detailed analysis of WWDM free streaming under various modified expansion histories, providing new constraints on WWDM parameters from observational data.

Findings

Constraints on WWDM parameters from Lyman-alpha forest data

Impact of early matter domination on WWDM free streaming

Effect of early dark energy on structure formation

Abstract

In models of warm dark matter, there is an appreciable population of high momentum particles in the early universe, which free stream out of primordial over/under densities, thereby prohibiting the growth of structure on small length scales. The distance that a dark matter particle travels without obstruction, known as the free streaming length, depends on the particle's mass and momentum, but also on the cosmological expansion rate. In this way, measurements of the linear matter power spectrum serve to probe warm dark matter as well as the cosmological expansion history. In this work, we focus on ultra-light wave wave dark matter (WWDM) characterized by a typical comoving momentum $q_\ast$ and mass $m$. We first derive constraints on the WWDM parameter space $(q_\ast, m)$ using Lyman-$\alpha$ forest observations due to a combination of the free-streaming effect and the white-noise effect. We next assess how the free streaming of WWDM is affected by three modified expansion histories: early matter domination, early dark energy, and very early dark energy.