Dipolar Dark Matter

TL;DR

This paper investigates how dark matter with electric or magnetic dipole moments interacts with nucleons, constraining its properties using experimental data and exploring models that explain signals like DAMA while remaining consistent with null results.

Contribution

It provides new bounds on the dipole moments of dark matter and identifies parameter spaces where Dirac and Majorana fermions can explain experimental signals and relic density.

Findings

DM with <10 GeV mass can fit DAMA and null experiments if Dirac.

Majorana DM with >38 GeV mass and specific mass splitting can explain DAMA and relic density.

Some parameter space is testable at LHC.

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_\chi > 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.