Impact of a Rapid Diluted Energy Density on the halo mass function

TL;DR

This paper investigates how early-universe energy density features, modeled as Gaussian bumps in the matter power spectrum, influence the halo mass function and power spectrum, revealing distinctive effects for intermediate halo masses through simulations and analytical methods.

Contribution

It introduces a parametric family of Gaussian bumps in the matter power spectrum to study their impact on halo formation, combining simulations and analytical models for accurate predictions.

Findings

Distinctive effects on halo mass function for masses between 10^{12.3} and 10^{13.6} h^{-1} M_sun.

Analytical predictions align well with N-body simulation results.

Halos outside the specified mass range are minimally affected by primordial bumps.

Abstract

We study dark energy cosmological models, extensions of the standard model of particles, characterized by having an extra relativistic energy density at very early times, and that rapidly dilute after a phase transition occurs. These models generate well localized features (or bumps) in the matter power spectrum for modes crossing the horizon around and before the phase transition epoch. This is because the presence of the additional energy component enhances the growth of matter fluctuations during the radiation dominated epoch. Instead of considering a particular model, we focus on a parametric family of Gaussian bumps in the matter power spectrum, which otherwise would be a $\Lambda$CDM one. We study the evolution of such bump cosmologies and their effects in the halo mass function and halo power spectrum using N-body simulations, the halo-model based HMcode method, and the peak background split framework. The bumps are subject to different nonlinear effects that become physically well understood, and from them we are able to predict that the most distinctive features will show up for intermediate halo masses $10^{12.3} \,h^{-1}M_{\odot} < M < 10^{13.6} \,h^{-1}M_{\odot}$. Out of this range, we expect halos are not significantly affected regardless of the location of the primordial bump in the matter power spectrum. Our analytical results are accurate and in very satisfactory agreement with the simulated data.