Directly Deflecting Particle Dark Matter

We propose a new strategy to directly detect light particle dark matter that has long-ranged interactions with ordinary matter. The approach involves distorting the local flow of dark matter with time-varying fields and measuring these distortions with shielded resonant detectors. We apply this idea to sub-MeV dark matter particles with very small electric charges or coupled to a light vector mediator, including the freeze-in parameter space targeted by low mass direct detection efforts. This approach can probe dark matter masses ranging from 10 MeV to below a meV, extending beyond the capabilities of existing and proposed direct detection experiments.

Figure 1

Schematic of the experimental concept. Dark matter passing through an oscillating electric field is deflected, setting up propagating waves of alternating dark matter millicharge ${\rho }_{\chi }$ and millicurrent $j_{\chi }$ densities. Dark matter waves flow unimpeded through an electromagnetic shield, creating small electromagnetic fields that can be measured with a resonant $LC$ circuit inductively coupled to a magnetometer (not depicted) inside the shielded detector region.

Figure 2

The anticipated reach to millicharged dark matter in the $q_{\mathrm{eff}}-m_{\chi }$ plane for various experimental configurations of our setup at 90% C.L., compared to existing constraints (shaded gray). In all cases, we assume a year of integration time, a spatially averaged field strength of $⟨E_{\mathrm{def}}⟩=10\mathrm{kV}/\mathrm{cm}$, and $\omega =100\mathrm{kHz}$. The green line corresponds to the projected reach of a detector optimized for detection of magnetic fields, such as the DM Radio experiment [6]. The reach of dedicated $LC$ resonators optimized for detecting electric fields is also shown. The lines labeled $E$-field (I-III) correspond to various deflector or shield volumes, $LC$ circuit temperatures, and quality factors as indicated in the legend. Also shown are the direct detection sensitivities of 1-year exposures for the near-term planned experiments SENSEI (100 g) (purple) [7, 8] and SuperCDMS-G2 (1 kg) (yellow) [1], assuming zero background. Longer-term R&D on direct detection concepts with meV-scale energy thresholds (such as detectors using superconductors [9], Dirac materials [10], or polar crystals [11, 12] as targets) could extend direct detection sensitivity to keV-scale DM masses. Along the solid blue line, the millicharge abundance from freeze-in production in the early Universe is in agreement with the observed dark matter energy density. We also show an estimate of a limit derived from a test of Coulomb’s law as a dashed gray line [13, 14].