Observational constraints on dark matter scattering with electrons

We present new observational constraints on the elastic scattering of dark matter with electrons for dark matter masses between 10 keV and 1 TeV. We consider scenarios in which the momentum-transfer cross section has a power-law dependence on the relative particle velocity, with a power-law index $n\in \{-4,-2,0,2,4,6\}$. We search for evidence of dark matter scattering through its suppression of structure formation. Measurements of the cosmic microwave background temperature, polarization, and lensing anisotropy from Planck 2018 data and of the Milky Way satellite abundance measurements from the Dark Energy Survey and Pan-STARRS1 show no evidence of interactions. We use these datasets to obtain upper limits on the scattering cross section, comparing them with exclusion bounds from electronic recoil data in direct detection experiments. Our results provide the strongest bounds available for dark matter–electron scattering derived from the distribution of matter in the Universe, extending down to sub-MeV dark matter masses, where current direct detection experiments lose sensitivity.

Figure 1

The 95% CLqueryAU: Journal style defines abbreviation C.L. as “confidence limits” and considers it a common definition. To better fit journal style and avoid confusion, this has been changed to CL throughout. Please make sure your meaning was retained. upper limits on ${\sigma }_0$, the coefficient of the momentum-transfer cross section for DM–electron scattering, as a function of DM mass. The cross section scales as $v^n$, as indicated in the plots, where $v$ is the relative velocity of scattering particles. The shaded region above each line is excluded by (left) Planck 2018 CMB temperature, polarization, and lensing power spectra at the 95% CL and (right) the Milky Way satellite abundance from DES and Pan-STARRS1.

Figure 2

Transfer functions for velocity-independent DM scattering with electrons (solid) and protons (dotted) ruled out at 95% confidence based on the 6.5 keV thermal relic WDM constraint from Milky Way satellite galaxies (black) [20]. We show the transfer functions at two extreme DM masses: 10 keV (red) and 1 TeV (blue).

Figure 3

Comparison of the CMB (red) and Milky Way satellite (blue) results from this work and the exclusion bounds from electronic-recoil direct detection experiments and FIRAS spectral distortions (gray) [11]. We show recent direct detection bounds from Xenon1T [34] and SENSEI@MINOS [38] for $F_{\mathrm{DM}}=1$ (top), $F_{\mathrm{DM}}=\alpha m_e/q$ (middle), and $F_{\mathrm{DM}}=(\alpha m_e/q{)}^2$ (bottom); shaded regions for Xenon10 [30] and protoSENSEI@MINOS [36] incorporate ceiling calculations from Ref. [45]. We translate available cosmological limits for $n=0$ (top), $n=-2$ (middle), and $n=-4$ (bottom) to the quantity ${\overline{\sigma }}_e$ defined in Eq. (7).

Figure 4

The 95% CL upper limits on ${\sigma }_0$, the coefficient of the momentum-transfer cross section for DM-proton scattering, as a function of DM mass. The cross section scales as $v^n$, as indicated in the plots, where $v$ is the relative velocity of scattering particles. The shaded region above each line is excluded by Planck 2018 CMB temperature, polarization, and lensing power spectra.