Is Dark Matter with Long-Range Interactions a Solution to All Small-Scale Problems of $\Lambda$ Cold Dark Matter Cosmology?

The cold dark matter 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 dark matter 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.

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-core problem. The crosses indicate two benchmark models for which detailed simulations [44] have found a solution to the too-big-to-fail problem. Dashed and solid lines show contours of the astrophysical relevant quantities ${\sigma }_{\max }^T$ and $v_{\max }$. See the 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 $M_{\mathrm{cut}}$ of the smallest protohalos. $M_{\mathrm{cut}}\gtrsim 5\times {10}^{10}{M}_{\odot }$ is excluded by Lyman-$\alpha$ data, while $M_{\mathrm{cut}}\gtrsim {10}^9{M}_{\odot }$ may solve the small-scale abundance problems of $\Lambda \mathrm{CDM}$ cosmology.