Abstract
Light halo dark matter (DM) particles upscattered by high-energy cosmic rays (CRs) can be energetic, and become detectable by conventional direct detection experiments. The current constraints derived from space-based direct CR measurements can reach O(10−31) cm2 for a constant DM-nucleon scattering cross section. We show that if the CR energy spectrum follows a power law of type ∼E−3, the derived constraints on the scattering cross section will be highly insensitive to DM particle mass. This suggests that ultrahigh-energy CRs (UHECRs) indirectly measured by ground-based detectors can be used to place constraints on ultralight DM particles, as E−3 is a very good approximation of the UHECR energy spectrum up to energy ∼1020 eV. Using the recent UHECR flux data, we show that the current constraints derived from space-based CR measurements can in principle be extended to ultralight DM particles far below eV scale.
Highlights
Compelling astrophysical evidence supports the existence of dark matter (DM) in the Universe, whether or not DM participates non-gravitational interactions is still an open question
For a DM particle with mass mχ ∼ 1 GeV and a typical DM escape velocity ∼ 540 km s−1, the elastic scattering off a target nucleus with mass ∼ 100 GeV leads to a maximal recoil energy ∼ 0.06 keV which is significantly lower than the typical detection threshold
We show that as long as the energy spectrum of cosmic rays (CRs) flux follows a power law ∼ E−α with α 3, the derived constraints on the DM-nucleon scattering cross section will not decrease towards lower DM mass
Summary
Compelling astrophysical evidence supports the existence of dark matter (DM) in the Universe, whether or not DM participates non-gravitational interactions is still an open question. From the recent UHECR nucleus flux data, we obtain the following results: the constraints on the spin-independent DM-nucleon scattering cross section can be 10−(32−31) cm for DM particle mass down to extremely small value ∼ 10−12 eV, which expands the currently known constraints derived from spacebased direct CR measurements by around ten orders of magnitude in DM mass, and close a large previously unconstrained parameter space; the most stringent constraints are found to be at DM mass ∼ 10−5 eV and ∼ 10−11 eV, due to the “knee” and “toe” structure in the UHECR flux, respectively; this CRDM approach will completely loss sensitivity for DM mass below 10−14 eV as the UHECR flux is highly suppressed above ∼ 1020 eV, a phenomena possibly related to the scatterings between UHECRs and cosmic microwave background (CMB) photons [34, 35].
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