Magnetic Inelastic Dark Matter

TL;DR

The paper addresses the DAMA–null-results tension by proposing Magnetic Inelastic Dark Matter (MiDM), wherein a WIMP with a magnetic dipole couples to iodine and undergoes inelastic transitions to an excited state. It analyzes two scattering channels—dipole-dipole (DD) and dipole-charge (DZ)—and also contemplates dark-sector mediators, providing cross-section forms and illustrating how MiDM can fit the DAMA modulation while remaining consistent with other experiments. A key feature is the possible de-excitation photon of order ~100 keV produced inside detectors, which, along with the lifetime of the excited state, yields distinctive signals and potential complications for standard nuclear-recoil cuts. The work highlights significant, testable predictions for XENON100, KIMS, and CRESST, while stressing the need for better calculations of the nuclear magnetic dipole form factor to sharpen the viable MiDM parameter space.

Abstract

Iodine is distinguished from other elements used in dark matter direct detection experiments both by its large mass as well as its large magnetic moment. Inelastic dark matter utilizes the large mass of iodine to allay tensions between the DAMA annual modulation signature and the null results from other experiments. We explore models of inelastic dark matter that also take advantage of the second distinct property of iodine, namely its large magnetic moment. In such models the couplings are augmented by magnetic, rather than merely electric, interactions. These models provide simple examples where the DAMA signal is compatible with all existing limits. We consider dipole moments for the WIMP, through conventional magnetism as well as "dark" magnetism, including both magnetic-magnetic and magnetic-electric scattering. We find XENON100 and CRESST should generically see a signal, although suppressed compared with electric inelastic dark matter models, while KIMS should see a modulated signal comparable to or larger than that of DAMA. In a large portion of parameter space, de-excitation occurs promptly, producing a ~ 100 keV photon inside large xenon experiments alongside the nuclear recoil. This effect could be searched for, but if not properly considered may cause nuclear recoil events to fail standard cuts.

Figures (3)

• Figure 1: The weighted-atomic mass and weighted-magnetic dipole moment (Eq. (\ref{['eqn:weighteddipole']}) in units of the nuclear magneton $\mu_{{N}}$ of various dark matter search targets. (C,O and Ca,Ar have been shifted slightly so as not to overlay each other.)
• Figure 2: Allowed ranges of parameter space for inelastic scattering of a magnetic dipole (dominated by dipole-dipole scattering for iodine). Purple (dark) and blue (light) regions are 90% and 99% allowed confidence intervals, respectively, for a $\chi^2$ fit to the DAMA modulation. Constraints are: CDMS (solid), CRESST-II (short light dashed), XENON10 (short dark dashed), KIMS (long dark dashed), and ZEPLIN-III (long light dashed). In the upper row, we utilized only the $2-8~$keVee bins in DAMA, and in the lower row we used the entire range of $2-14~$keVee. This serves to illustrate the strong dependence of the allowed DAMA parameter space for heavy dark matter on the dipole form factor's behavior at high $E_R$ as discussed in Sec. \ref{['sec:formfactor']} in detail.
• Figure 3: Allowed ranges of parameter space for dark dipole scattering with mediator mass $m_{A^\prime} = 70{~\rm MeV}$. In this plot, we have set the dark gauge coupling $\alpha_d = \alpha$. Lines are labeled as in Fig. \ref{['fig:dipoledipoleregions']}. In the upper row, we utilized only the $2-8~$keVee bins in DAMA, and in the lower row we used the entire range of $2-14~$keVee. This serves to illustrate the strong dependence of the allowed DAMA parameter space for heavy dark matter on the dipole form factor's behavior at high $E_R$ as discussed in Sec. \ref{['sec:formfactor']} in detail.