Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy

Abstract

Recent advances in γ-ray cosmic ray, infrared and radio astronomy have allowed us to develop a significantly better understanding of the galactic medium properties in the last few years. In this work using the DRAGON code, that numerically solves the CR propagation equation and calculating γ-ray emissivities in a 2-dimensional grid enclosing the Galaxy, we study in a self consistent manner models for the galactic diffuse γ-ray emission. Our models are cross-checked to both the available CR and γ-ray data. We address the extend to which dark matter annihilations in the Galaxy can contribute to the diffuse γ-ray flux towards different directions on the sky. Moreover we discuss the impact that astrophysical uncertainties of non DM nature, have on the derived γ-ray limits. Such uncertainties are related to the diffusion properties on the Galaxy, the interstellar gas and the interstellar radiation field energy densities. Light ∼10 GeV dark matter annihilating dominantly to hadrons is more strongly constrained by γ-ray observations towards the inner parts of the Galaxy and influenced the most by assumptions of the gas distribution; while TeV scale DM annihilating dominantly to leptons has its tightest constraints from observations towards the galactic center avoiding the galactic disk plane, with the main astrophysical uncertainty being the radiation field energy density. In addition, we present a method of deriving constraints on the dark matter distribution profile from the diffuse γ-ray spectra. These results critically depend on the assumed mass of the dark matter particles and the type of its end annihilation products.

Composite dark matter and LHC interplay

“…Note that for ξ = 0.1 the antiproton bound, at least adopting the KOL propagation models, can also rule out the right boundary of the funnel-shaped region (i.e. the vertical line corresponding to m η 80 GeV); this confirms the expected result that DM annihilation into bb with a cross-section of the order of the thermal value σv rel 3 × 10 −26 cm 3 s −1 is in tension with the limit extracted from the antiproton spectrum measured by the PAMELA experiment considering values of DM mass up to ∼ 100 GeV [96]. 20 19 It is worth noting that this is a distinctive feature of the composite model.…”

A couplet from flavored dark matter

“…Similar to the case of positron constraints being most sensitive to prompt positrons in the final state, indirect detection in photons is most sensitive to τ 's in the final state, since more photons are produced from τ 's than from e's or µ's. One can therefore formulate the bound from indirect detection in the photon final state [24] in terms of the effective annihilation cross section leading to the production of τ 's,…”

“…where σv bound,γ is the experimental bound quote in [24] for a Majorana DM annihilating to τ + τ − with 100% branching ratio. The constraint from indirect detection in photons is shown in figure 3 as the green-shaded region.…”

Neutrino self-interactions

“…Having pointed out that, our LSP's mass is far below the detection threshold. At the same time severe constraints on light DM annihilations from the CMB [27] and diffuse gamma ray emission [28] do not apply, because the LSP annihilates into invisible neutrino pairs via its U (1) X interaction. 5) Of course, untouched by these considerations is the possibility to enlarge the particle content to obtain a (self-interacting) CDM relic.…”