Abstract
We initiate the study of novel thermal dark matter (DM) scenarios where present-day annihilation of DM in the galactic center produces boosted stable particles in the dark sector. These stable particles are typically a subdominant DM component, but because they are produced with a large Lorentz boost in this process, they can be detected in large volume terrestrial experiments via neutral-current-like interactions with electrons or nuclei. This novel DM signal thus combines the production mechanism associated with indirect detection experiments (i.e. galactic DM annihilation) with the detection mechanism associated with direct detection experiments (i.e. DM scattering off terrestrial targets). Such processes are generically present in multi-component DM scenarios or those with non-minimal DM stabilization symmetries. As a proof of concept, we present a model of two-component thermal relic DM, where the dominant heavy DM species has no tree-level interactions with the standard model and thus largely evades direct and indirect DM bounds. Instead, its thermal relic abundance is set by annihilation into a subdominant lighter DM species, and the latter can be detected in the boosted channel via the same annihilation process occurring today. Especially for dark sector masses in the 10 MeV–10 GeV range, the most promising signals are electron scattering events pointing toward the galactic center. These can be detected in experiments designed for neutrino physics or proton decay, in particular Super-K and its upgrade Hyper-K, as well as the PINGU/MICA extensions of IceCube. This boosted DM phenomenon highlights the distinctive signatures possible from non-minimal dark sectors.
Highlights
Background RatesThe atmospheric neutrino backgrounds have been measured by Super-K over a 10.7 year period, during runs SK-I (1489 days), SK-II (798 days), SK-III (518 days) and SK-IV (1096 days), and the final results are summarized in Ref. [73]
This complementarity is lost when the interaction is due to a light mediator [106,107,108], which applies to our case where ψB interacts with SM states via an O(10 MeV) dark photon
We presented a novel dark matter (DM) scenario which incorporates the successful paradigm of WIMP thermal freeze-out, yet evades stringent constraints from direct and indirect detection experiments, and predicts a novel signal involving boosted DM
Summary
Consider two species of fermion DM ψA and ψB with Dirac masses mA > mB, which interact via a contact operator. To achieve a sufficiently large flux of boosted ψB particles, we need a large number density of ψA particles in the galactic halo For this reason, we will focus on somewhat low mass thermal DM, with typical scales: mA O(10 GeV), mB O(100 MeV), mγ O(10 MeV). We will focus on somewhat low mass thermal DM, with typical scales: mA O(10 GeV), mB O(100 MeV), mγ O(10 MeV) [52,53,54], both components in an inelastic DM multiplet can be cosmologically stable, such that the current day annihilation is not suppressed These splittings, would typically soften the bounds on the non-relativistic component of ψA/ψB from conventional direct detection experiments, since the scattering would be inelastic (either endothermic or exothermic).
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