Electromagnetic properties of dark matter: Dipole moments and charge form factor

Vernon Barger,Wai-Yee Keung,Danny Marfatia

doi:10.1016/j.physletb.2010.12.008

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.

Highlights

The nature of the dark matter (DM) particle is unknown
The interaction occurs through the electric dipole moment (EDM) or the magnetic dipole moment (MDM) of dark matter
For comparable short distance cutoffs, we find that an EDM may give the dominant contribution to DM-nucleus scattering because it directly couples to the nuclear charge

Summary

Introduction

The nature of the dark matter (DM) particle is unknown. There are many well studied scenarios guided by theoretical niceties such as the Minimal Supersymmetric Standard Model, models with extra dimensions, and the Little Higgs Models with T -parity, all of which posit that the DM particle interacts primarily via weak interactions. The interaction occurs through the electric dipole moment (EDM) or the magnetic dipole moment (MDM) of dark matter. The interactions are described by dimension-5 operators for non-self-conjugate particles, such as Dirac DM, but not for Majorana DM. For comparable short distance cutoffs, we find that an EDM may give the dominant contribution to DM-nucleus scattering because it directly couples to the nuclear charge. In the EDM case, the recoil energy ER distribution is highly enhanced in the low ER region as 1/(vr2ER) (where vr is the speed of the DM particle in the rest frame of the nucleus) in contrast with that from MDM which goes as 1/ER. We provide analytic expressions for the scattering cross sections for the MDM and EDM cases with careful expansions in the relative velocity and recoil energy. The operator has a structure that is similar to that of the spin-independent (SI) interaction

Electric dipole moment of dark matter

Magnetic dipole moment of dark matter

Electric charge form factor of dark matter

Analysis