Abstract
We consider photon signals arising from the annihilation or decay of low-mass (sub-GeV) dark matter which couples dominantly to quarks. In this scenario, the branching fractions to the various kinematically accessible hadronic final states can largely be determined from chiral perturbation theory. Several of these final states yield striking spectral features in the sub-GeV photon spectrum. New experiments, such as e-ASTROGAM and AMEGO, are in development to improve sensitivity in this energy range, and we discuss their potential sensitivity to this class of models.
Highlights
There has been much recent interest in dark matter models in which the candidate particle has a mass ≲OðGeVÞ
If we denote by Iexp the exposure of the instrument, and by ΔΩ the solid angle viewed, the number of events due to dark matter annihilation or decay expected to be observed within the energy window E− ≤ Eobs ≤ Eþ is given by while the number of expected events observed is given by
We have considered the indirect detection of sub-GeV dark matter annihilation or decay
Summary
There has been much recent interest in dark matter models in which the candidate particle has a mass ≲OðGeVÞ. It has recently been pointed out that, if sub-GeV dark matter couples predominantly to quarks, the indirect detection signatures are striking [9,10,11,12,13,14] This is because there are few kinematically accessible particles when the center-pofffi-ffimass energy of the annihilation or decay process is s ≲ OðGeVÞ, and those particles tend tpoffiyffi ield fairly striking photon signatures. Our main assumption will be that primary electroweak interactions are negligible; the primary products of dark matter annihilation or decay will consist only of light mesons, with photons produced only by meson decay. For this purpose, we will find that the most important final states are those containing an η, which decays to γγ with ∼40% branching fraction. We will take mπ0 ∼ mπÆ 1⁄4 mπ, as this approximation will only have a non-negligible effect very near the threshold for πÆ production
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