Three Exceptions for Thermal Dark Matter with Enhanced Annihilation to Gamma Gamma

Abstract

Recently, there have been hints for dark matter (DM) annihilation in the galactic center to one or more photon lines. In order to achieve the observed photon line flux, DM must have a relatively large effective coupling to photons, typically generated radiatively from large couplings to charged particles. When kinematically accessible, direct annihilation of DM to these charged particles is far too large to accommodate both the DM relic density and constraints from the observed flux of continuum photons from the galactic center, halo and dwarf galaxies. We discuss three exceptions to these obstacles, generating the observed line signal while providing the correct relic density and evading photon continuum constraints. The exceptions are (i) coannihilation, where the DM density is set by interactions with a heavier state that is not populated today, (ii) forbidden channels, where DM annihilates to heavier states that are kinematically blocked today, but open in the early Universe, and (iii) asymmetric DM, where the relic density is set by a primordial asymmetry. We build simple models to realize these scenarios.

14 pages, 9 figures; discussion expanded, refs added, minor numerical errors and typos corrected, conclusions unchanged

References in corpus (19)

• Asymmetric Dark Matter
• A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope
• Turning off the Lights: How Dark is Dark Matter?
• Electromagnetic properties of dark matter: dipole moments and charge form factor
• Magnetic Inelastic Dark Matter
• How Dark Are Majorana WIMPs? Signals from MiDM and Rayleigh Dark Matter
• Gamma Ray Line Constraints on Effective Theories of Dark Matter
• Fermi 130 GeV gamma-ray excess and dark matter annihilation in sub-haloes and in the Galactic centre
• Dipolar Dark Matter
• Loop-induced dark matter direct detection signals from gamma-ray lines
• Two Lines or Not Two Lines? That is the Question of Gamma Ray Spectra
• The WIMP Forest: Indirect Detection of a Chiral Square
• Dark matter line search using a joint analysis of dwarf galaxies with the Fermi Gamma-ray Space Telescope
• Explaining PAMELA and WMAP data through Coannihilations in Extended SUGRA with Collider Implications
• Gamma-ray Lines in the Fermi Data: is it a Bubble?
• Searching for the continuum spectrum photons correlated to the 130 GeV gamma-ray line
• Increasing the Neutralino Relic Abundance with Slepton Coannihilations: Consequences for Indirect Dark Matter Detection
• Statistical interpretation of the spatial distribution of current 130 GeV gamma-ray line signal within the dark matter annihilation scenario
• Dipole-interacting Fermionic Dark Matter in positron, antiproton, and gamma-ray channels