Resonant scattering and recombination of pseudo-degenerate WIMPs
  We consider the direct and indirect detection signatures of WIMPs \chi^0 in kinematic regimes with a heavier, but nearly degenerate, charged state \chi^{+-}. For small splittings of O(10) MeV, the scattering of WIMPs off nuclei may be dominated by inelastic recombination processes mediated by the formation of (\chi^- N) bound states, leading to a distinct signature for direct detection. These cross-sections are bound primarily by limits on the abundance of heavy isotopes, and may be considerably larger than the elastic scattering cross section in more conventional models. If the mass splitting is too large for recombination to occur, there may still be a significant resonant enhancement of loop-induced electromagnetic form-factors of the WIMP, which can enhance the elastic scattering cross-section. We also discuss how this regime affects the annihilation cross-section and indirect detection signatures, and note the possibility of a significant mono-energetic \gamma-signal, mediated by resonant processes near the (\chi^+\chi^-) bound state threshold. 
Maxim Pospelov, Adam Ritz