Dark matter halos in the multicomponent model. Substructure and density profiles of galactic halos*

Multicomponent dark matter with inter-conversions of mass eigenstates into one another is known to successfully and simultaneously resolve $\Lambda$CDM problems at galactic and sub-galactic scales. Here, we present $N$-body simulations of the simplest two-component (2cDM) model with large set of velocity-dependent cross-sections, $\sigma(v)\propto v^{a}$, and compare them with observational data. They show that the 2cDM paradigm with the self-interaction cross-sections $0.01\le \sigma_0/m\le 1$~cm$^2$g$^{-1}$ and the mass degeneracy $\Delta m/m\sim 10^{-7}-10^{-8}$ robustly resolves the substructure and too-big-to-fail problems by suppressing the substructure with $V_{\rm circ,max} \lesssim100$~km~s$^{-1}$. Furthermore, 2cDM robustly suppresses central cusps in dwarf halos with $M \sim 4-5 \times10^{11} M_{\odot}$, thus resolving the core-cusp problem as well. The core radii are controlled by $\sigma_0/m$ and the DM cross-section's velocity-dependent power-law indices $(a_s,a_c)$, but are largely insensitive to the species' mass degeneracy. Next, there is disagreement between the radial distribution of dwarfs in a host halo observed in the Local Group and simulated with CDM, which poses one more small-scale problem to CDM, which is alleviated by 2cDM.