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Dark matter interpretation of recent electron and positron data

Lars Bergstrom, Joakim Edsjo, Gabrijela Zaharijas

TL;DR

This paper evaluates whether the Fermi-LAT measurement of the combined electron–positron spectrum can be explained by dark matter annihilation or decay. It compares two DM archetypes—direct leptonic annihilation (favoring μ⁺μ⁻ final states) and annihilation through a light mediator (AH/N models)—using DarkSUSY with a MED propagation model and an isothermal halo, and incorporates boost factors from substructure and Sommerfeld effects. The fits to Fermi and PAMELA data require large enhancement factors (~10³), with the μ⁺μ⁻ channel providing the best agreement; gamma-ray and radio constraints depend strongly on the assumed halo profile, excluding steeper halos but remaining viable for isothermal halos. The study highlights a potential final state radiation signature in diffuse gamma rays as a discriminating test and notes that future gamma-ray data will be crucial to confirm or rule out the DM interpretation.

Abstract

We analyze the recently released Fermi-LAT data on the sum of electrons and positrons. Compared to a conventional, pre-Fermi, background model, a surprising excess in the several hundred GeV range is found and here we analyze it in terms of dark matter models. We also compare with newly published results from PAMELA and HESS, and find models giving very good fits to these data sets as well. If this dark matter interpretation is correct, we also predict the possibility of a sharp break in the diffuse gamma ray spectrum coming from final state radiation.

Dark matter interpretation of recent electron and positron data

TL;DR

This paper evaluates whether the Fermi-LAT measurement of the combined electron–positron spectrum can be explained by dark matter annihilation or decay. It compares two DM archetypes—direct leptonic annihilation (favoring μ⁺μ⁻ final states) and annihilation through a light mediator (AH/N models)—using DarkSUSY with a MED propagation model and an isothermal halo, and incorporates boost factors from substructure and Sommerfeld effects. The fits to Fermi and PAMELA data require large enhancement factors (~10³), with the μ⁺μ⁻ channel providing the best agreement; gamma-ray and radio constraints depend strongly on the assumed halo profile, excluding steeper halos but remaining viable for isothermal halos. The study highlights a potential final state radiation signature in diffuse gamma rays as a discriminating test and notes that future gamma-ray data will be crucial to confirm or rule out the DM interpretation.

Abstract

We analyze the recently released Fermi-LAT data on the sum of electrons and positrons. Compared to a conventional, pre-Fermi, background model, a surprising excess in the several hundred GeV range is found and here we analyze it in terms of dark matter models. We also compare with newly published results from PAMELA and HESS, and find models giving very good fits to these data sets as well. If this dark matter interpretation is correct, we also predict the possibility of a sharp break in the diffuse gamma ray spectrum coming from final state radiation.

Paper Structure

This paper contains 5 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. Dark matter and propagation models
  3. Data and backgrounds
  4. Results of fits
  5. Conclusions and discussion

Figures (2)

  • Figure 1: The $2\sigma$ contours in the enhancement factor - mass plane for a) annihilation to $\mu^+\mu^-$, b) the Nomura-Thaler model N3 and c) the Arkani-Hamed et al. model AH4. The contours are shown for PAMELA and Fermi, whereas the HESS data is only used as an upper limit. The black dot is the example model shown in Fig.\ref{['fig:spec']}.
  • Figure 2: Spectra for examples of good fit models in \ref{['fig:boost']}. The signal and background are shown for electrons ($e^+ + e^-$) together with Fermi fermicre and HESS data hesshessle. The HESS data and the background model has been rescaled with a factor 0.85. In the inset, the positron fraction as measured with PAMELA is shown together with the predicted signal for the same model.