Boosting hierarchical structure formation with scalar-interacting dark matter

TL;DR

This study uses N-body simulations to show that scalar-interacting dark matter models lead to earlier halo formation and extended steady accretion phases, potentially explaining high-redshift reionization and galaxy survival issues.

Contribution

It demonstrates that scalar interactions in dark matter models significantly alter structure formation timelines compared to standard LCDM.

Findings

Dark matter haloes form earlier in scalar-interacting models.

The transition from merger to steady accretion occurs at higher redshifts.

Enhanced high-redshift structure formation may explain reionization and galaxy survival.

Abstract

We investigate the effect of long-range scalar interactions in dark matter (DM) models of cosmic structure formation with a particular focus on the formation times of haloes. Utilising $N$-body simulations with $512^3$ DM particles we show that in our models dark matter haloes form substantially earlier: tracing objects up to redshift $z\sim6$ we find that the formation time, as characterised by the redshift $z_{1/2}$ at which the halo has assembled half of its final mass, is gradually shifted from $z_{1/2}\approx 1.83$ in the fiducial LCDM model to $z_{1/2}\approx 2.54$ in the most extreme self-interaction model. This is accompanied by a shift of the redshift that marks the transition between merger and steady accretion epochs from $z_{*}\approx 4.32$ in the \lcdm\ halos to $z_{*}\approx 6.39$ in our strongest interaction model. In other words, the scalar-interacting model employed in this work produces more structures at high redshifts, prolonging at the same time the steady accretion phases. These effects taken together can help the LCDM model to account for a high redshift reionisation as indicated by the WMAP data and can alleviate issues related to the survival of the thin-disk dominated galaxies at low redshifts.