Cosmological simulations with rare and frequent dark matter self-interactions

Abstract

Dark matter (DM) with self-interactions is a promising solution for the small-scale problems of the standard cosmological model. Here we perform the first cosmological simulation of frequent DM self-interactions, corresponding to small-angle DM scatterings. The focus of our analysis lies in finding and understanding differences to the traditionally assumed rare DM (large-angle) self scatterings. For this purpose, we compute the distribution of DM densities, the matter power spectrum, the two-point correlation function and the halo and subhalo mass functions. Furthermore, we investigate the density profiles of the DM haloes and their shapes. We find that overall large-angle and small-angle scatterings behave fairly similarly with a few exceptions. In particular, the number of satellites is considerably suppressed for frequent compared to rare self-interactions with the same cross-section. Overall we observe that while differences between the two cases may be difficult to establish using a single measure, the degeneracy may be broken through a combination of multiple ones. For instance, the combination of satellite counts with halo density or shape profiles could allow discriminating between rare and frequent self-interactions. As a by-product of our analysis, we provide - for the first time - upper limits on the cross-section for frequent self-interactions.

A Heavy QCD Axion and the Mirror World

“…and is highly dependent on the speed v. Typical speeds in (dwarf galaxies, galaxies, galaxy clusters) are (30, 300, 1000)km s −1 . Numerical N-body simulations, including only dark matter, show that on galactic scales a velocity-independent σ T /m of 1g/cm 2 leads to significant departures from CDM simulations [62]. These departures are seen for several observables, including the matter power spectrum, halo and subhalo mass functions, the number of satellites, halo density and circular velocity profiles, and halo shape distributions.…”

Sensitivity of halo shape measurements

“…In the case of the ellipsoidal shells, there also exists a lower limit on r2 ell . In practice, we used the same implementation as previously used in Fischer et al (2022).…”

“…In this section, we explain how we measured the shape of simulated DM haloes and investigated their accuracy. We used the four most massive haloes of the full box cosmological simulations presented in Fischer et al (2022). They have total masses of about ∼10 14 M and are therefore considered low-mass galaxy clusters.…”

“…The maximal physical Plummer-equivalent gravitational softening length is 1.4 kpc. The same analysis as in Fischer et al (2022) to identify the substructure and compute corresponding quantities such as the halo mass and the virial radius was employed, that is, we used SubFind (Springel et al 2001;Dolag et al 2009). We computed the total mass, M, as the sum of the gravitationally bound particles as identified by SubFind.…”

“…Moreover, we used the simulations with the highest resolution (N = 576 3 , m DM = 4.37 × 10 7 M h −1 ) for collisionless cold dark matter (CDM) and fSIDM with a momentum transfer cross-section of σ T /m = 0.1 cm 2 g −1 (Kahlhoefer et al 2014;Fischer et al 2021b). For further details, readers can refer to Fischer et al (2022).…”