Is dark matter with long-range interactions a solution to all small-scale problems of ΛCDM cosmology?

TL;DR

This paper proposes a dark-matter paradigm with a light vector mediator that couples DM to neutrinos, producing velocity-dependent self-interactions and a late kinetic decoupling. The resulting small-scale cutoff $M_{\rm cut}$ can lie in the dwarf-galaxy regime (roughly $10^9$–$10^{10} M_\odot$), while remaining compatible with Lyman-$\alpha$ constraints; a one-to-one mapping between particle parameters $(m_\chi,m_V)$ and astrophysical observables $(v_{\max},\sigma_T^{\max})$ shows viable regions that address the cusp–core and too-big-to-fail problems. The model also yields a large Sommerfeld-enhanced annihilation cross section into $VV$ with neutrinofinal states, offering potential IceCube signatures, though collider and direct-detection prospects are challenging. Overall, the authors argue that a simple light-vector-mediated IDM can simultaneously resolve multiple small-scale tensions of $\Lambda$CDM and motivate targeted astrophysical and neutrino observations as tests. The work highlights a minimally extended framework with clear observational handles on both structure formation and high-energy neutrino astronomy.

Abstract

The cold dark matter (DM) paradigm describes the large-scale structure of the universe remarkably well. However, there exists some tension with the observed abundances and internal density structures of both field dwarf galaxies and galactic satellites. Here, we demonstrate that a simple class of DM models may offer a viable solution to all of these problems simultaneously. Their key phenomenological properties are velocity-dependent self-interactions mediated by a light vector messenger and thermal production with much later kinetic decoupling than in the standard case.

Figures (3)

• Figure 1: Interaction processes that set the DM relic density and may lead to observable neutrino annihilation products today (left), change the inner velocity and density profile of dwarf halos (middle) and induce a comparatively large cutoff in the spectrum of primordial density perturbations (right).
• Figure 2: The white area corresponds to DM and mediator masses that may solve the 'cusp vs. core' problem. The crosses indicate two benchmark models for which detailed simulations Vogelsberger:2012ku have found a solution to the 'too big to fail' problem. Dashed and solid lines show contours of the astrophysical relevant quantities $\sigma^T_{\rm max}$ and $v_{\rm max}$. See text for further details.
• Figure 3: This plane shows the mediator mass $m_{V}$ vs. the coupling strength $g_\nu$. Large values of $g_\nu$ and small values of $m_{V}$ lead to late kinetic decoupling and thus a large mass $M_{\rm cut}$ of the smallest protohalos. $M_{\rm cut}\gtrsim5\times10^{10}M_\odot$ is excluded by Ly-$\alpha$ data while $M_{\rm cut}\gtrsim10^{9}M_\odot$ may solve the small-scale abundance problems of $\Lambda$CDM cosmology.