Dipolar Dark Matter

TL;DR

The paper examines dark matter models that couple electromagnetically via electric or magnetic dipole moments, including transition moments for Majorana states. It derives the relevant elastic and inelastic scattering cross sections, computes direct-detection rates, and confronts these with XENON, CDMS, DAMA, and COGENT data, as well as LEP/L3 collider bounds. Relic-density arguments are used to map the dipole moments to cosmological abundance, yielding tight bounds on the moments and identifying regions where DAMA can be reconciled with null experiments, particularly in low-mass or inelastic scenarios. The work also highlights potential collider and LHC signatures, emphasizing that dipolar interactions could be testable across direct-detection and collider experiments under specific mass and splitting ranges.

Abstract

If dark matter (DM) has non-zero direct or transition, electric or magnetic dipole moment then it can scatter nucleons electromagnetically in direct detection experiments. Using the results from experiments like XENON, CDMS, DAMA and COGENT we put bounds on the electric and magnetic dipole moments of DM. If DM consists of Dirac fermions with direct dipole moments, then DM of mass less than 10 GeV is consistent with the DAMA signal and with null results of other experiments. If on the other hand DM consists of Majorana fermions then they can have only non-zero transition moments between different mass eigenstates. We find that Majorana fermions with mass m_χ> 38 GeV and mass splitting of the order of (50-200) keV can explain the DAMA signal and the null observations from other experiments and in addition give the observed relic density of DM by dipole-mediated annihilation. This parameter space for the mass and for dipole moments is allowed by limits from L3 but may have observable signals at LHC.

Figures (8)

• Figure 1: Electromagnetic scattering of a proton with DM with non-zero dipole moments.
• Figure 2: Plot shows the allowed regions for DM electric dipole moment with varying DM mass for elastic scattering for different experiments. Shaded region shows the allowed parameter space for DAMA which is consistent with all other experiments.
• Figure 3: Plot of DM electric dipole moment against the mass difference $\delta$ for inelastic scattering for different experiments. Shaded region shows the allowed parameter space for DAMA which is consistent with all other experiments and in case of $m_\chi>38$ GeV it is also consistent with the relic density.
• Figure 4: Plot of allowed DM mass and mass splitting $\delta$ for a fixed $\mathcal{D}$ which gives the correct relic density of DM.
• Figure 5: Plot shows the allowed regions for DM magnetic dipole moment with varying DM mass for elastic scattering for different experiments. Shaded region shows the allowed parameter space for DAMA which is consistent with all other experiments.