Cosmological Simulations with Dark Matter from beyond the Standard Model

Abstract

We study the non-linear structure formation in cosmologies where the collision-less cold dark matter (CDM) is either replaced by interacting dark matter or (partly) replaced by a free-streaming non-cold dark matter component. We focus in the first case on models with a non-vanishing interaction cross-section between dark matter and radiation in the early Universe, i.e. photons (γCDM) and neutrinos (νCDM).
We study the properties of the dark matter structures that form in the presence of the collisional damping using N-Body simulations. For their halo shapes, we find similar effects as for standard thermalized fermionic Warm Dark Matter (WDM).
However, for the abundance of these structures, the interacting DM models are clearly distinguishable from WDM below the characteristic damping scale. We also have a closer look at dark matter halos that resemble those hosting the two main galaxies in our Local Group, the Milky Way (MW) and Andromeda (M31).
By using a high-resolution zoom-simulation of Local Group-like environments, we reveal how the DM-radiation interactions help to ease certain CDM ”small scale problems”. Furthermore, the combination of these Local Group simulations with our previous cosmological simulations allows us to constrain the cross-section in our model by comparing the abundance of satellite galaxies in our Milky Way with the predictions for subhaloes. Thanks to the sensitivity of the subhalo abundance to the suppression of the primordial perturbations, even our most conservative constraints are orders of magnitude tighter than those previously obtained from CMB data.
In the case of neutrinos or other non-cold dark matter, we study ways to predict numerically the evolution of this free-streaming component correctly. We identify shortcomings in all the previously proposed techniques we encountered in our studies of various models with massive neutrinos and come up with a new, adaptive Eulerian technique to treat the neutrino fluid accurately. In particular, we introduce our implementation called SEPARA. First test results for the code are presented while full cosmological simulations will be performed in the near future.