Cosmology: small scale issues revisited

TL;DR

This paper reviews small-scale challenges to the standard cold dark matter model in galaxy formation, discussing observational issues and implications for warm dark matter alternatives, suggesting current evidence favors LambdaCDM with possible mild warm variants.

Contribution

It provides a comprehensive review of small-scale issues in LambdaCDM and explores the implications for warm dark matter models based on current observational constraints.

Findings

Current evidence is consistent with LambdaCDM.

Warm dark matter cannot be very warm without conflicting with observations.

Data may favor a mild warm dark matter scenario.

Abstract

The abundance of dark matter satellites and subhalos, the existence of density cusps at the centers of dark matter halos, and problems producing realistic disk galaxies in simulations are issues that have raised concerns about the viability of the standard cold dark matter (LambdaCDM) scenario for galaxy formation. This article reviews these issues, and considers the implications for cold vs. various varieties of warm dark matter (WDM). The current evidence appears to be consistent with standard LambdaCDM, although improving data may point toward a rather tepid version of LambdaWDM -- tepid since the dark matter cannot be very warm without violating observational constraints.