N-body Simulations of cosmologies with Light Massive Relics

TL;DR

This paper presents the first cosmological N-body simulations incorporating Light Massive Relics (LiMRs), exploring their nonlinear effects on structure formation and their interplay with standard neutrinos, to aid future particle physics constraints.

Contribution

It develops a novel simulation framework to model LiMRs' impact on nonlinear cosmological scales, including their degeneracies with neutrinos, which was not previously achieved.

Findings

LiMRs affect the matter power spectrum and halo properties.

Simulations show degeneracies between LiMRs and neutrinos in cosmological observables.

Framework enables detailed analysis of LiMR phenomenology in cosmology.

Abstract

The presence of additional relativistic particles at the time of recombination can be inferred through their contribution to $\Delta N_{\rm eff}$. If these species have a finite but low mass (Light Massive Relics - LiMRs), they act as a hot subcomponent of dark matter and impact late-time structure formation. Understanding these effects will be crucial to pin down the underlying particle physics properties of any future $\Delta N_{\rm eff}$ detection. While their impact has been well-studied on linear scales, this work develops the framework for and presents results from the first set of cosmological N-body simulations that can track the effects of LiMRs, as a function of their mass and temperature, down to fully nonlinear scales. Importantly, our simulations model the impact of both the massive Standard Model neutrinos and LiMRs, which will be crucial in disentangling possible degeneracies. We systematically explore the effects of LiMR properties such as mass, temperature, and initial distribution, on various cosmological observables, including the total matter power spectrum, Halo Mass Functions (HMF), Mass-Concentration relation, radial halo profiles, and weak lensing signals around massive clusters. The framework and simulations developed here will enable detailed follow-up of the rich phenomenology of LiMR cosmologies.