Self-Interacting Dark Matter

TL;DR

Subgalactic-scale issues in standard cold dark matter motivate exploring self-interacting dark matter (SIDM). The authors test SIDM using Monte Carlo scattering in N-body simulations and reanalyze constraints from detectors, focusing on a cross-section per unit mass around 0.5–6 cm^2/g. Their simulations show that self-interactions produce cored, more isotropic halos and can reduce substructure, while too-large cross sections suppress halo formation; they also assess exotic-hadron dark matter, finding constrained but not excluded regions, with XQC/balloon/space data providing key limits. Overall, the work supports SIDM as a viable modification to CCDM for subgalactic scales and highlights specific experimental strategies to probe these models.

Abstract

Spergel and Steinhardt have recently proposed the concept of dark matter with strong self-interactions as a means to address numerous discrepancies between observations of dark matter halos on subgalactic scales and the predictions of the standard collisionless dark matter picture. We review the motivations for this scenario and discuss some recent, successful numerical tests. We also discuss the possibility that the dark matter interacts strongly with ordinary baryonic matter, as well as with itself. We present a new analysis of the experimental constraints and re-evaluate the allowed range of cross-section and mass.

Figures (3)

• Figure 1: Comparison of halo profiles for non-interacting (solid) and self-interacting dark matter with cross-sections $\sigma_{DD} =10^{-24}\,$cm$^2$GeV$^{-1}$ (dashed) and $\sigma_{DD}=10^{-23}\,$cm$^2$GeV$^{-1}$ (dot-dashed). Halos are chosen from a descending range of masses, with the four largest halos in our simulation shown in the leftmost column Three short rays corresponding to logarithmic slopes $0.5$, $1$ and $1.5$ are shown to guide the eye in the inner part of the halo
• Figure 2: Histogrammed distribution of inner halo slopes $\alpha$ for non-interacting (solid) and self-interacting dark matter with cross-section $\sigma_{DD} =10^{-24}\,$cm$^2$GeV$^{-1}$ (dashed) and $\sigma_{DD}=10^{-23}\,$cm$^2$GeV$^{-1}$ (dot-dashed). We only include halos with more than 1000 particles, corresponding to masses greater than $3.6\times 10^9$$M_\odot$
• Figure 3: Plot of the dark matter-proton scattering cross section $\sigma_{Dp}$ versus dark matter particle mass $m$ showing current experimental limits. The constraints from the XQC, IMP7/8 and IMAX experiments are new; the constraints from Pioneer and Skylab experiments have been re-evaluated. The grey region shows the range of dark matter-dark matter cross-section $\sigma_{DD}$ in Eq. (2). The strip is displayed to study the possibility that dark matter consists of exotic hadrons in which $\sigma_{DD}/m$ and $\sigma_{Dp}/m$ are comparable. The square marks the values corresponding to a nucleon, which is similar to what is expected for some of the most attractive candidates for dark matter. The new results appear to rule out the low mass range, but allow masses greater than $10^5$ GeV.