Boosting hierarchical structure formation with scalar-interacting dark matter

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. Utilizing N-body simulations with 5123 DM particles we show that in our models DM haloes form substantially earlier: tracing objects up to redshift z ∼ 6 we find that the formation time, as characterized by the redshift z1/2 at which the halo has assembled half of its final mass, is gradually shifted from z1/2 ≈ 1.83 in the fiducial Λ cold dark matter (ΛCDM) model to z1/2 ≈ 2.54 in the most extreme scalar-interaction model. This is accompanied by a shift of the redshift that marks the transition between merger and steady accretion epochs from z* ≈ 4.32 in the ΛCDM haloes to z* ≈ 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 ΛCDM model to account for a high-redshift reionization as indicated by the Wilkinson Microwave Anisotropy Probe (WMAP) data and can alleviate issues related to the survival of the thin-disc-dominated galaxies at low redshifts.