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Leptophilic Dark Matter in Direct Detection Experiments and in the Sun

Joachim Kopp, Viviana Niro, Thomas Schwetz, Jure Zupan

TL;DR

The paper investigates leptophilic dark matter using a model‑independent EFT framework, focusing on four direct-detection channels: WIMP-electron scattering, elastic and inelastic WIMP-atom scattering, and loop-induced WIMP-nucleus scattering. It shows that many operators are velocity-suppressed, while unsuppressed ones lead to a hierarchy of signals with loop-induced WNS often dominating unless symmetry forbids it. Direct-detection data (CDMS, XENON-10, CoGeNT, DAMA) constrain the leptophilic parameter space, and while DAMA can be fit in some cases, the overall picture remains incompatible with null results, especially when including Super-Kamiokande solar-neutrino bounds. Neutrino signals from DM annihilation in the Sun provide complementary constraints, reinforcing the conclusion that leptophilic DM cannot simultaneously explain DAMA/CoGeNT and satisfy other experimental bounds. Overall, the work maps a rich phenomenology for leptophilic DM but rules out its ability to resolve the DAMA/CoGeNT tensions under the considered frameworks.

Abstract

Dark matter interacting predominantly with leptons instead of nuclear matter has received a lot of interest recently. In this talk, we investigate the signals expected from such 'leptophilic Dark Matter' in direct detection experiments and in experiments looking for Dark Matter annihilation into neutrinos in the Sun. In a model-independent framework, we calculate the expected interaction rates for different scattering processes, including elastic and inelastic scattering off atomic electron shells, as well as loop-induced scattering off atomic nuclei. In those cases where the last effect dominates, leptophilic Dark Matter cannot be distinguished from conventional WIMPs. On the other hand, if inelastic scattering off the electron shell dominates, the expected event spectrum in direct detection experiments is different and would provide a distinct signal. However, we find that the signals in DAMA and/or CoGeNT cannot be explained by invoking leptophilic DM because the predicted and observed energy spectra do not match, and because of neutrino bounds from the Sun.

Leptophilic Dark Matter in Direct Detection Experiments and in the Sun

TL;DR

The paper investigates leptophilic dark matter using a model‑independent EFT framework, focusing on four direct-detection channels: WIMP-electron scattering, elastic and inelastic WIMP-atom scattering, and loop-induced WIMP-nucleus scattering. It shows that many operators are velocity-suppressed, while unsuppressed ones lead to a hierarchy of signals with loop-induced WNS often dominating unless symmetry forbids it. Direct-detection data (CDMS, XENON-10, CoGeNT, DAMA) constrain the leptophilic parameter space, and while DAMA can be fit in some cases, the overall picture remains incompatible with null results, especially when including Super-Kamiokande solar-neutrino bounds. Neutrino signals from DM annihilation in the Sun provide complementary constraints, reinforcing the conclusion that leptophilic DM cannot simultaneously explain DAMA/CoGeNT and satisfy other experimental bounds. Overall, the work maps a rich phenomenology for leptophilic DM but rules out its ability to resolve the DAMA/CoGeNT tensions under the considered frameworks.

Abstract

Dark matter interacting predominantly with leptons instead of nuclear matter has received a lot of interest recently. In this talk, we investigate the signals expected from such 'leptophilic Dark Matter' in direct detection experiments and in experiments looking for Dark Matter annihilation into neutrinos in the Sun. In a model-independent framework, we calculate the expected interaction rates for different scattering processes, including elastic and inelastic scattering off atomic electron shells, as well as loop-induced scattering off atomic nuclei. In those cases where the last effect dominates, leptophilic Dark Matter cannot be distinguished from conventional WIMPs. On the other hand, if inelastic scattering off the electron shell dominates, the expected event spectrum in direct detection experiments is different and would provide a distinct signal. However, we find that the signals in DAMA and/or CoGeNT cannot be explained by invoking leptophilic DM because the predicted and observed energy spectra do not match, and because of neutrino bounds from the Sun.

Paper Structure

This paper contains 5 sections, 7 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Leptophilic Dark Matter
  3. Exclusion limits on leptophilic Dark Matter from direct detection experiments
  4. Neutrinos from Dark Matter annihilation in the Sun
  5. Conclusions

Figures (3)

  • Figure 1: The momentum space electron wave functions of iodine and sodium. Thick colored curves correspond to shells that contribute to WIMP-electron scattering in DAMA, while thin light curves correspond to electrons that are too tightly bound to be separated from the atom in a WIMP interaction at DAMA energies. The approximate wave functions shown here are taken from ref. Bunge:1993a. They do not include relativistic corrections (which can lead to flattening at high momentum) or multi-electron correlations.
  • Figure 2: DM-nucleus interaction induced by a charged lepton loop and photon exchange.
  • Figure 3: Left: CDMS, XENON-10, and Super-Kamiokande exclusion limits and DAMA/CoGeNT-favored values for the WIMP mass $m_\chi$ and the WIMP--fre electron scattering cross section $\sigma_e^0$. Right: comparison of the observed annual modulation spectrum in DAMA to the prediction for leptophilic DM. The solid curve has been fitted to the DAMA data from 2--8 keV, while for the dashed curve, the first energy bin has been neglected. The top row of panels is for $V \otimes V$ interactions, while the bottom row is for $A \otimes A$ interactions.