WarmAndFuzzy: the halo model beyond CDM

TL;DR

WarmAndFuzzy is a new computational tool that extends the halo model to include warm and fuzzy dark matter, enabling the analysis of their non-linear effects on the matter power spectrum, which was previously unexplored for fuzzy dark matter.

Contribution

This paper introduces the first halo model calculation for fuzzy dark matter and provides a publicly available code incorporating WDM and FDM into the standard halo model framework.

Findings

Differences between WDM, FDM, and CDM persist at low redshifts.

The code models ultralight axions and thermal WDM.

Cores in halo profiles are under development and expected to have minor effects.

Abstract

Cold dark matter (CDM) is a well established paradigm to describe cosmological structure formation, and works extraordinarily well on large, linear, scales. Progressing further in dark matter physics requires being able to understand structure formation in the non-linear regime, both for CDM and its alternatives. This short note describes a calculation, and accompanying code, WarmAndFuzzy, incorporating the popular models of warm and fuzzy dark matter (WDM and FDM) into the standard halo model to compute the non-linear matter power spectrum. The FDM halo model power spectrum has not been computed before. The FDM implementation models ultralight axions and other scalar fields with $m_a\approx 10^{-22}\text{ eV}$. The WDM implementation models thermal WDM with mass $m_X\approx 1\text{ keV}$. The halo model shows that differences between WDM, FDM, and CDM survive at low redshifts in the quasi-linear and fully non-linear regimes. The code uses analytic transfer functions for the linear power spectrum, modified collapse barriers in the halo mass function, and a modified concentration-mass relationship for the halo density profiles. Modified halo density profiles (for example, cores) are not included, but are under development. Cores are expected to have very minor effects on the power spectrum on observable scales. Applications of this code to the Lyman-$\alpha$ forest flux power spectrum and the cosmic microwave background lensing power spectrum will be discussed in companion papers. \textsc{WarmAndFuzzy} is available online at \url{https://github.com/DoddyPhysics/HMcode}, where collaboration in development is welcomed.