The impact of inelastic self-interacting dark matter on the dark matter structure of a Milky Way halo

Abstract

We study the effects of inelastic dark matter self-interactions on the internal structure of a simulated Milky Way (MW)-size halo. Self-interacting dark matter (SIDM) is an alternative to collisionless cold dark matter (CDM) which offers a unique solution to the problems encountered with CDM on sub-galactic scales. Although previous SIDM simulations have mainly considered elastic collisions, theoretical considerations motivate the existence of multi-state dark matter where transitions from the excited to the ground state are exothermic. In this work, we consider a self-interacting, two-state dark matter model with inelastic collisions, implemented in the Arepo code. We find that energy injection from inelastic self-interactions reduces the central density of the MW halo in a shorter timescale relative to the elastic scale, resulting in a larger core size. Inelastic collisions also isotropize the orbits, resulting in an overall lower velocity anisotropy for the inelastic MW halo. In the inner halo, the inelastic SIDM case (minor-to-major axis ratio $s\equiv c/a\approx 0.65$) is more spherical than the CDM ($s\approx 0.4$), but less spherical than the elastic SIDM case ($s\approx 0.75$). The speed distribution $f(v)$ of dark matter particles at the location of the Sun in the inelastic SIDM model shows a significant departure from the CDM model, with $f(v)$ falling more steeply at high speeds. In addition, the velocity kicks imparted during inelastic collisions produce unbound high-speed particles with velocities up to 500 km s${}^{-1}$ throughout the halo. This implies that inelastic SIDM can potentially leave distinct signatures in direct detection experiments, relative to elastic SIDM and CDM.

16 pages, 10 figures

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• Cosmological and idealized simulations of dark matter haloes with velocity-dependent, rare and frequent self-interactions
• Unraveling the interplay between SIDM and baryons in MW halos: defining where baryons dictate heat transfer
• The role of baryons in self-interacting dark matter mergers
• Manifesting hidden dynamics of a sub-component dark matter
• SIDM Concerto: Compilation and Data Release of Self-interacting Dark Matter Zoom-in Simulations
• Unequal-mass mergers of dark matter haloes with rare and frequent self-interactions
• Cosmological simulations with rare and frequent dark matter self-interactions
• Calibrating the SIDM Gravothermal Catastrophe with N-body Simulations
• The Non-universal Pseudo Phase-Space Density Profiles of Symphony Host Halos