Abstract
Multilevel dark matter with diagonal and off-diagonal interactions shows a rich phenomenology in its self-scattering. If the interactions are mediated by a particle that is less massive than the dark matter, the Sommerfeld effect can lead to resonant enhancement of the scattering. For mediators lighter than the level separation, dark matter particles can upscatter to excited states and deexcite by emitting these mediators. We compute these cross sections, both above and below the kinematic threshold, in a generic two-component dark matter model and identify the large inelastic cross section as a result of maximal mixing between the two states. A new route for cooling of large dark matter halos and a new drag force between two colliding halos are identified and shown to arise purely from the inelastic scattering.
Highlights
Galaxies are observed to be surrounded by more massive halolike structures made of a substance whose particle nature still remains unknown
We have studied the self-scattering of a twolevel dark matter (DM) model
The off-diagonal interaction leads to inelastic scattering of a pair of DM particles from the ground state to the excited state, in addition to the ordinary elastic scattering
Summary
Galaxies are observed to be surrounded by more massive halolike structures made of a substance whose particle nature still remains unknown. When this pressure equates the gravitational pull on the matter, any further accumulation of DM at the center ceases and a stable core is formed While these interactions may be obtained with massive mediators, the cross section in such models is velocity independent and strongly constrained from various observations [20]. The energy dissipation from the inelastic scattering, followed by deexcitation, might lead to a significant change in the shape and density profile of DM halos Some of these features have been discussed in the context of atomic DM models in Refs. IV, conclude with a summary of our results and avenues for future work
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