Halo Shape and Relic Density Exclusions of Sommerfeld-Enhanced Dark Matter Explanations of Cosmic Ray Excesses

TL;DR

It is shown that the required enhancement implies thermal relic densities that are too small to be all of dark matter, and that the dark matter is sufficiently self-interacting that observations of elliptical galactic dark matter halos exclude large Sommerfeld enhancement for light force carriers.

Abstract

Dark matter with Sommerfeld-enhanced annihilation has been proposed to explain observed cosmic ray positron excesses in the 10 GeV to TeV energy range. We show that the required enhancement implies thermal relic densities that are too small to be all of dark matter. We also show that the dark matter is sufficiently self-interacting that observations of elliptical galactic dark matter halos exclude large Sommerfeld enhancement for light force carriers. Resonant Sommerfeld enhancement does not modify these conclusions, and the astrophysical boosts required to resolve these discrepancies are disfavored, especially when significant self-interactions suppress halo substructure.

Figures (2)

• Figure 1: Regions above the contours are excluded by the relic density constraint and by halo ellipticity observations for the $m_\phi$ indicated. The classical approximation used to obtain the halo bounds becomes inaccurate for $m_\phi \agt 100~\text{MeV}$.
• Figure 2: Upper bounds on Sommerfeld enhancement factor $S$ from relic density (solid), along with PAMELA- and Fermi-favored regions and the best fit point $(m_X, S) = (2.35~\text{TeV}, 1500)$Bergstrom:2009fa, all for $m_{\phi} = 250~\text{MeV}$. Halo shape bounds are also shown for the values of $m_\phi$ indicated (dashed).