Abstract
It was recently suggested that dark matter consists of ~GeV particles that carry baryon number and mix with the neutron. We demonstrate that this could allow for resonant dark matter-neutron oscillations in the early universe, at finite temperature, leading to low-scale baryogenesis starting from a primordial dark matter asymmetry. In this scenario, the asymmetry transfer happens around 30 MeV, just before big bang nucleosynthesis. We illustrate the idea using a model with a dark U(1)' gauge interaction, which has recently been suggested as a way of addressing the neutron lifetime anomaly. The asymmetric dark matter component of this model is both strongly self-interacting and leads to a suppression of matter density perturbations at small scales, allowing to mitigate the small-scale problems of cold dark matter cosmology. Future CMB experiments will be able to consistently probe, or firmly exclude, this scenario.
Highlights
One of the curious coincidences of the ΛCDM cosmological model is the rough similarity of the contributions from baryons and dark matter (DM) to the energy density, Ωb ≃ 0.049 versus ΩCDM ≃ 0.26 [1], given that in typical scenarios of the early Universe they have completely different origins
An appealing feature of many models of asymmetric DM is that this coincidence could be due to DM having a mass at the GeV scale, like baryons, and a shared mechanism for the generation of the two asymmetries
This could be achieved through either a common “cogenesis” event that creates the required asymmetries in the dark and visible sector, or through an efficient sharing of asymmetries created in independent ways, though sphalerons, new renomalizable interactions, or higher-dimensional effective operators
Summary
One of the curious coincidences of the ΛCDM cosmological model is the rough similarity of the contributions from baryons and dark matter (DM) to the energy density, Ωb ≃ 0.049 versus ΩCDM ≃ 0.26 [1], given that in typical scenarios of the early Universe they have completely different origins. We will show that it is possible to explain both the baryon asymmetry and the neutron decay anomaly within the same model, while at the same time evading all cosmological bounds, if mγ0 ∼ 60 keV and an additional species of dark radiation ν0 is introduced to enable the decay γ0 → ν0ν0. This entails moderate tension with BBN and CMB limits on extra radiation species, implying that it may be testable already in the near future. Larger mγ0 consistent with γ0 → eþe−, and without the need of introducing the additional degrees of freedom contributed by ν0, can be accommodated if we disregard the neutron lifetime anomaly
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