Direct Detection of Multi-component Secluded WIMPs

Abstract

Dark matter candidates comprising several sub-states separated by a small mass gap, and coupled to the Standard Model by (sub-)GeV force carriers, can exhibit non-trivial scattering interactions in direct detection experiments. We analyze the secluded U(1)-mediated WIMP scenario, and calculate the elastic and inelastic cross sections for multi-component WIMP scattering off nuclei. We find that second-order elastic scattering, mediated by virtual excited states, provides strong sensitivity to the parameters of the model for a wide range of mass splittings, while for small splittings the WIMP excited states have lifetimes exceeding the age of the universe, and generically have a fractional relative abundance above 0.1%. This generates even stronger constraints for mass splittings less than 200 keV due to exothermic de-excitation events in detectors.

Figures (6)

• Figure 1: First and second Born amplitudes for $\chi_1$-nucleus scattering.
• Figure 2: Endothermic inelastic scattering constraints. 90% CDMS confidence limits on $\kappa$ as a function of vector mass $m_V$ for a 200 GeV WIMP, with $\alpha'$ chosen to yield the correct thermal relic abundance. We show constraints from the endothermic scattering $\chi_1 N\rightarrow \chi_2 N$ for $\Delta m=0$ (solid), 100 keV (dashed), and 150 keV (dotted). No endothermic events are expected in this case for splittings above $\Delta m \sim 190$ keV.
• Figure 3: Elastic scattering constraints: 90% CDMS confidence limits on $\kappa$ as a function of WIMP mass $m_\chi$ for a mass splitting $\Delta m= 10$ MeV, with $\alpha'$ chosen to yield the correct thermal relic abundance. We show constraints from the elastic scattering $\chi_1 N\rightarrow \chi_1 N$ for $m_V$ = 100 MeV (solid) and 10 MeV (dashed).
• Figure 4: Elastic scattering constraints: 90% CDMS confidence limits on $\kappa$ as a function of vector mass $m_V$ for a 200 GeV WIMP with mass splitting $\Delta m =10$ MeV, where $\alpha'$ is chosen to yield the correct thermal relic abundance. We show constraints from elastic scattering $\chi_1 N\rightarrow \chi_1 N$, where the solid line interpolates between the nuclear and nucleon scattering descriptions.
• Figure 5: Exothermic inelastic scattering constraints. 90% CDMS confidence limits on $\kappa$ as a function of mass splitting $\Delta m$ for a vector mass $m_V=1$ GeV, where $\alpha'$ is chosen to yield the correct thermal relic abundance. We show constraints from exothermic inelastic scattering $\chi_2 N\rightarrow \chi_1 N$ for WIMPs with masses $m_\chi = 100 \,$GeV (solid) and 1 TeV (dashed). The constraints rapidly deteriorate for large $\Delta m$ as in this case most scatterings will have a large nuclear recoil well above the maximum detector sensitivity of $E_R = 100$ keV.