Detection of QCD axion dark matter by coherent scattering

The QCD axion is a promising candidate of the dark matter. In this paper, we discuss elastic scattering processes between nucleons and the QCD axion dark matter. We point out that the cross section can be enhanced by more than O(1025) by the coherent effect, compared to classical processes. As a result, for example, we show that QCD axions may scatter at the sun with O(1) probability for fa ??? 1011 GeV. In addition, one may expect stimulated emission effects can also enhance the cross section because the number density of the axion DM is very large. The enhancement factor can be as large as another O(1025) and, if the factor exists, the force from the dark matter wind may be detected via, e.g., torsion balance experiments. However, it is also found that there is a cancellation of the stimulated emission factor and the force is too small to be detected.

Automated summary

This paper discusses the elastic scattering processes between nucleons and the QCD axion dark matter, and points out that the cross section can be significantly enhanced by the coherent effect. Additionally, the stimulated emission effects and the high number density of the axion DM can further enhance the scattering cross section. However, the cancellation of the stimulated emission factor reduces the force to a small value that is difficult to detect.