Dark Matter Microhalos From Simplified Models

TL;DR

This paper introduces simplified models to study small-scale enhancements in the matter power spectrum and their effects on dark matter substructure and gravitational observables, applicable to various early universe scenarios.

Contribution

It presents a semi-analytic, model-independent approach to connect small-scale power spectrum features with dark matter halo formation and gravitational signals.

Findings

Bumps in the power spectrum lead to early-forming sub-solar mass halos.

These halos contribute significantly to dark matter substructure in galaxies.

Gravitational observables like pulsar timing are sensitive to small-scale power spectrum features.

Abstract

We introduce simplified models for enhancements in the matter power spectrum at small scales and study their implications for dark matter substructure and gravitational observables. These models capture the salient aspects of a variety of early universe scenarios that predict enhanced small-scale structure, such as axion-like particle dark matter, light vector dark matter, and epochs of early matter domination. We use a model-independent, semi-analytic treatment to map bumps in the matter power spectrum to early-forming sub-solar mass dark matter halos and estimate their evolution, disruption, and contribution to substructure of clusters and galaxies at late times. We discuss the sensitivity of gravitational observables, including pulsar timing arrays and caustic microlensing, to both the presence of bumps in the power spectrum and variations in their basic properties.