Novel Direct Detection Constraints on Light Dark Matter

Abstract

All attempts to directly detect particle dark matter (DM) scattering on nuclei suffer from the partial or total loss of sensitivity for DM masses in the GeV range or below. We derive novel constraints from the inevitable existence of a subdominant, but highly energetic, component of DM generated through collisions with cosmic rays. Subsequent scattering inside conventional DM detectors, as well as neutrino detectors sensitive to nuclear recoils, limits the DM-nucleon scattering cross section to be below 10 −31 cm 2 for both spin-independent and spin-dependent scattering of light DM.

Direct detection and complementary constraints for sub-GeV dark matter

“…The right panel of figure 1 clearly illustrates the exponential loss of sensitivity of conventional direct detection experiments to sub-GeV DM, reflecting the fact that non-relativistic DM particles with such small masses do not carry enough momentum to allow for nuclear recoils above the experimental threshold. As recently pointed out, however, there is a small yet inevitable component of relativistic DM that alleviates this limitation [28]: 3 if DM can elastically scatter with nuclei, then also the well-established population of high-energy cosmic rays will scatter on DM, thus accelerating them from essentially at rest (in the galactic frame) to GeV energies and beyond -in principle for arbitrarily small DM masses. In order to handle scattering via light mediators we extend the formalism developed in ref.…”

“…In order to handle scattering via light mediators we extend the formalism developed in ref. [28] to allow for arbitrary relativistic scattering amplitudes (rather than only a constant σ χN as assumed there). As the derivation follows the same steps as in ref.…”

“…As the derivation follows the same steps as in ref. [28], we only briefly state our results here and refer to that reference for further details (see also ref. [83]).…”

“…Here, ρ local χ and Φ LIS CR are the local interstellar DM density and the cosmic-ray flux, respectively, and T min CR is the minimal kinetic cosmic-ray energy needed to accelerate DM to kinetic energy T χ ; we take into account elastic scattering of cosmic-ray nuclei N = {p, 4 He} with DM, including in each case the same dipole form factor suppression as in ref. [28]. 4 D eff ∼ 8 kpc, finally, is an effective distance out to which we assume that the source density of CRDM is roughly the same as it is locally (which, for a standard DM distribution, corresponds to a sphere of about 10 kpc diameter).…”

“…Significant interest, both from the experimental and theoretical perspective, has thus turned to the possibility of DM particle masses below the GeV -TeV range. Conventional direct detection experiments are essentially insensitive to such light particles -except for very large scattering cross sections, where cosmic rays can upscatter DM to relativistic energies [28] -but new methods and concepts are being developed to overcome these difficulties [29][30][31][32][33][34].…”