Remarks on bosonic super-WIMP search experiments

Bosonic super–weakly interacting massive particles (WIMPs), including pseudoscalar and vector particles, are dark-matter candidates. To date, many underground experiments searches for super-WIMPs have been performed in the mass range of a few $\mathrm{keV}/c^2$ to $1\mathrm{MeV}/c^2$. All these searches utilize the absorption process of a super-WIMP by a target atom in the detector, which is similar to the photoelectric effect. We consider another process—namely, a Compton-like process. As an example, we compare the cross section of a germanium atom for the absorption process with that of a Compton-like process. Our findings indicate that the cross section for the Compton-like process becomes dominant relative to that for the absorption process for mass above approximately $150\mathrm{keV}/c^2$ for both pseudoscalar and vector super-WIMPs. In particular, the cross section for the Compton-like process for a vector super-WIMP becomes increasingly greater than that for the absorption process by 1 to 2 orders of magnitude in the $400\mathrm{keV}/c^2$ to $1\mathrm{MeV}/c^2$ mass range, respectively. By including the Compton-like process, which has not been used in any other super-WIMP search experiments, the experimental upper limits can be improved.

Figure 1

Cross sections (unit, b/atom) for the absorption and Compton-like processes, and the total cross section, including both processes, for the pseudoscalar (left panel) and vector (right panel) super-WIMPs as a function of the mass. We used the dimensionless coupling constant $g_{aee}=1$ (kinetic mixing parameter $\kappa =1$) for a pseudoscalar (vector) super-WIMP.