Electromagnetic properties of dark matter: dipole moments and charge form factor
Vernon Barger, Wai-Yee Keung, Danny Marfatia
TL;DR
The paper investigates electromagnetic interactions of dark matter through electric dipole moments, magnetic dipole moments, and a charge form factor, deriving complete cross sections and recoil spectra for these interactions. It shows that EDM scattering is strongly enhanced at low recoil via $d\sigma/dE_R \propto 1/(v_r^2 E_R)$ and provides a comprehensive MDM treatment including nuclear charge and magnetic contributions, plus a dimension-6 CFF framework linking to spin-independent scattering. The authors apply the formalism to a 7 GeV DM scenario, demonstrating that EDM, MDM, or CFF can reconcile CoGeNT’s low-energy excess with null results from XENON10, and they quantify the parameter choices and fit quality. The work clarifies how electromagnetic DM interactions map onto conventional SI cross sections and establishes benchmark scales $\Lambda_{EDM}$, $\Lambda_{MDM}$, and $\Lambda_{CFF}$ relevant for direct detection experiments and solar capture.
Abstract
A neutral dark matter particle may possess an electric dipole moment (EDM) or a magnetic dipole moment (MDM), so that its scattering with nuclei is governed by electromagnetic interactions. If the moments are associated with relevant operators of dimension-5, they may be detectable in direct search experiments. We calculate complete expressions of the scattering cross sections and the recoil energy spectra for dark matter with these attributes. We also provide useful formulae pertinent to dark matter that interacts via an electric charge form factor (CFF) which is related to the charge radius defined by an effective dimension-6 operator. We show that a 7 GeV dark matter particle with an EDM, MDM or CFF easily reproduces the CoGeNT excess while remaining consistent with null searches.