Low-mass constraints on WIMP effective models of inelastic scattering using the Migdal effect (2407.16187v2)

Abstract: We use the Migdal effect to extend to low masses the bounds on each of the effective couplings of the non-relativistic effective field theory of a WIMP of mass $m_\chi$ and spin 1/2 that interacts inelastically with nuclei by either upscattering to a heavier state with mass splitting $\delta>0$ or by downscattering to a lighter state with $\delta<0$. In order to do so we perform a systematic analysis of the Migdal bounds in the $m_\chi-\delta$ parameter space comparing them to those from nuclear recoil searches. The Migdal effect allows to significantly extend to low WIMP masses the nuclear recoil bounds for $\delta<0$. In this case the bounds are driven by XENON1T, except when $\delta$ is vanishing or very small, when, depending on the WIMP-nucleus interaction, in the lower end of the $m_\chi$ range either DS50 or SuperCDMS are more constraining. On the other hand, when $\delta>0$ and the WIMP particle upscatters to a heavier state nuclear recoil bounds are stronger than those from the Migdal effect.