Dark winds on the horizon: Prospects for detecting neutrino and hot dark matter wakes in large-scale structure

TL;DR

This paper investigates the potential to detect neutrino and hot dark matter wakes in large-scale structure, improving theoretical models and forecasting detection prospects in future surveys.

Contribution

It provides refined models and forecasts for detecting HDM wakes, highlighting their significance as indicators of free-streaming effects in cosmology.

Findings

Neutrino and HDM wakes are unlikely to be observed with 2D weak lensing surveys.

Ideal 3D maps can detect HDM wakes if the free-streaming length is sufficiently small.

HDM wakes uniquely indicate free-streaming effects, aiding in neutrino mass searches.

Abstract

We explore the cosmological signatures of neutrino and Hot Dark Matter (HDM) wakes, which refers to the preferential accumulation of neutrinos (or, more broadly, HDM particles) downstream of moving cold dark matter structures. We improve on existing theoretical models, and provide forecasts for the detectability of the effect in future surveys under more realistic conditions than previously considered in the literature. We show that neutrino and HDM wakes are unlikely to be ever observed with the most natural tracer of a hot subcomponent of the total dark matter on cosmological scales, i.e. 2D weak lensing surveys. However, the effect can be detected at a high significance with idealistic 3D maps of a tracer of HDM, for sufficiently small values of the effective free-streaming length (e.g. present-day values of $k_{\textrm{fs},0} \gtrsim 0.1\textrm{Mpc}^{-1}$ to reach $\textrm{SNR} \gtrsim 1$, for a HDM species accounting for a percent of the total dark matter). HDM wakes are a smoking gun of the effects of free-streaming, which cannot be mimicked by changes to the background expansion history (such as allowing for the dark energy to be dynamical), and hence offer another avenue to search for massive neutrinos, and hot subcomponents of the total dark matter more broadly, in a way that complements traditional observables.