Abstract
We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than v^{n}∼(10^{-(2-3)})^{n}, where n=1, 2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be σ∼0.1-1 barn, moderately larger than for standard model deuteron fusion, indicating a dark nuclear scale Λ∼O(100 MeV). Dark fusion firmly predicts constant σv below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometers per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.
Highlights
We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the smallscale structure problems of the cold collisionless dark matter paradigm
It has recently been noted that dark matter that interacts with itself with a nuclear-scale cross section can compactly account for many of these observations [3,4]
A number of authors working with a wide variety of model assumptions have concluded that synthesis of bound states of dark matter particles is a generic consequence of the high temperature history of such hidden sectors [5,6,7,8,9,10,11,12,13]
Summary
We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the smallscale structure problems of the cold collisionless dark matter paradigm. We relate the fusion to the elastic scattering cross section by σfv1;cm 1⁄4 fðb; v1;cmÞσel under the assumption that all dark sector dynamics are at the same scale.
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