Clustering with Light (but Massive) Relics

TL;DR

This paper investigates how Light (but Massive) Relics (LiMRs) influence early Universe matter clustering and weak lensing, revealing that eV-range LiMRs can be a significant dark matter component without conflicting with existing constraints.

Contribution

It introduces the impact of massive LiMRs on early matter clustering and weak lensing, proposing scenarios where they act as dark matter while evading $ abla N_{eff}$ constraints.

Findings

LiMRs with >1 eV mass can significantly contribute to dark matter.

LiMRs affect matter clustering and CMB lensing on small scales.

New scenarios where dark radiation transitions to matter before recombination.

Abstract

We consider the effect of Light (but Massive) Relics (LiMRs) on the clustering of matter in the early Universe. We account for the fact that LiMRs which are massive enough may cluster on large length scales at early times, and may thus impact weak lensing of the cosmic microwave background (CMB) even on small angular scales. In particular, we find that LiMRs in the $\gtrsim$ eV mass range (and even $> 10$ eV), can constitute a non-negligible component of dark matter. This opens up a class of scenarios in which energy is injected as dark radiation, but begins to redshift as matter before recombination, thus avoiding constraints on $\Delta N_{eff}$ while providing an eV-range dark matter component.