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High Energy Positrons and the WMAP Haze from Exciting Dark Matter

Ilias Cholis, Lisa Goodenough, Neal Weiner

TL;DR

This work investigates exciting dark matter (XDM), where a light mediator φ boosts annihilation products to produce high-energy e^± capable of explaining the INTEGRAL 511 keV signal, the HEAT positron excess, and the WMAP haze. By computing injection spectra for direct and muon decay channels, propagating cosmic rays with GALPROP, and testing three halo profiles, the authors connect XDM to HEAT and haze observations and generate PAMELA predictions. They find that XDM can account for the observed electronic anomalies across reasonable DM densities, with the positron fraction largely robust to halo choice but sensitive to propagation parameters and Alfvén velocity, and that the DM synchrotron component can match the haze under plausible magnetic-field and halo assumptions. The study implies that PAMELA should observe a notable high-energy positron signal for many parameter choices, providing a critical test of XDM as a unified source for multiple galactic electron/positron phenomena.

Abstract

We consider the signals of positrons and electrons from "exciting" dark matter (XDM) annihilation. Because of the light (m_phi ~< 1 GeV) force carrier phi into which the dark matter states can annihilate, the electrons and positrons are generally very boosted, yielding a hard spectrum, in addition to the low energy positrons needed for INTEGRAL observations of the galactic center. We consider the relevance of this scenario for HEAT, PAMELA and the WMAP "haze," focusing on light (m_phi ~< 2 m_pi) phi bosons, and find that significant signals can be found for all three, although significant signals generally require high dark matter densities. We find that measurements of the positron fraction are generally insensitive to the halo model, but do suffer significant astrophysical uncertainties. We discuss the implications for upcoming PAMELA results.

High Energy Positrons and the WMAP Haze from Exciting Dark Matter

TL;DR

This work investigates exciting dark matter (XDM), where a light mediator φ boosts annihilation products to produce high-energy e^± capable of explaining the INTEGRAL 511 keV signal, the HEAT positron excess, and the WMAP haze. By computing injection spectra for direct and muon decay channels, propagating cosmic rays with GALPROP, and testing three halo profiles, the authors connect XDM to HEAT and haze observations and generate PAMELA predictions. They find that XDM can account for the observed electronic anomalies across reasonable DM densities, with the positron fraction largely robust to halo choice but sensitive to propagation parameters and Alfvén velocity, and that the DM synchrotron component can match the haze under plausible magnetic-field and halo assumptions. The study implies that PAMELA should observe a notable high-energy positron signal for many parameter choices, providing a critical test of XDM as a unified source for multiple galactic electron/positron phenomena.

Abstract

We consider the signals of positrons and electrons from "exciting" dark matter (XDM) annihilation. Because of the light (m_phi ~< 1 GeV) force carrier phi into which the dark matter states can annihilate, the electrons and positrons are generally very boosted, yielding a hard spectrum, in addition to the low energy positrons needed for INTEGRAL observations of the galactic center. We consider the relevance of this scenario for HEAT, PAMELA and the WMAP "haze," focusing on light (m_phi ~< 2 m_pi) phi bosons, and find that significant signals can be found for all three, although significant signals generally require high dark matter densities. We find that measurements of the positron fraction are generally insensitive to the halo model, but do suffer significant astrophysical uncertainties. We discuss the implications for upcoming PAMELA results.

Paper Structure

This paper contains 32 sections, 12 equations, 17 figures, 9 tables.

Table of Contents

  1. Introduction
  2. Indirect Detection of Dark Matter
  3. Signals from Positrons and Electrons
  4. Direct Measurement of $e^{+}$ and $e^{-}$ Spectra
  5. High Energy Positron and Electron Signals in Synchrotron Radiation
  6. INTEGRAL/SPI
  7. Exciting Dark Matter (XDM)
  8. Calculations
  9. The Injection Spectra for $e^{+}$ $e^{-}$ Arising from DM Annihilation
  10. Dark Matter Density Functions (Halo Profiles)
  11. The Electron and Positron Backgrounds
  12. The Positron Fraction
  13. DM Synchrotron Radiation
  14. Uncertainties
  15. DM Halo Uncertainties
  16. ...and 17 more sections

Figures (17)

  • Figure 1: Diagrams contributing to annihilation of $\chi$.
  • Figure 2: Injection spectra of positrons.
  • Figure 3: Dark Matter density profiles.
  • Figure 4: Positron fraction backgrounds for $v_A = 0$, $v_A = 20$, and $v_A = 35$ km/s. The $\chi^2$ quoted is for the fit to the five lowest energy points.
  • Figure 5: Canonical models for $v_A = 0$ km/s.
  • ...and 12 more figures