Abstract
We propose a novel mechanism to explain the positron excesses, which are observed by satellite-based telescopes including PAMELA and AMS-02, in dark matter (DM) scenarios. The novelty behind the proposal is that it makes direct use of DM around the Galactic Center where DM populates most densely, allowing us to avoid tensions from cosmological and astrophysical measurements. The key ingredients of this mechanism include DM annihilation into unstable states with a very long laboratory-frame life time and their “retarded” decay near the Earth to electron-positron pair(s) possibly with other (in)visible particles. We argue that this sort of explanation is not in conflict with relevant constraints from big bang nucleosynthesis and cosmic microwave background. Regarding the resultant positron spectrum, we provide a generalized source term in the associated diffusion equation, which can be readily applicable to any type of two-“stage” DM scenarios wherein production of Standard Model particles occurs at completely different places from those of DM annihilation. We then conduct a data analysis with the recent AMS-02 data to validate our proposal.
Highlights
JHEP04(2018)093 the gamma-ray data from Milky Way satellite galaxies [15,16,17] often sets quite stringent limits on the allowed dark matter (DM) annihilation cross section, while they may be relaxed by dispersing the positron production zone with a long-lived intermediary state disintegrating to positrons [13]
We propose a novel mechanism to explain the positron excesses, which are observed by satellite-based telescopes including PAMELA and AMS-02, in dark matter (DM) scenarios
Regarding the resultant positron spectrum, we provide a generalized source term in the associated diffusion equation, which can be readily applicable to any type of two-“stage” DM scenarios wherein production of Standard Model particles occurs at completely different places from those of DM annihilation
Summary
Our mechanism is predicated upon a non-conventional situation, wherein DM particles annihilate or decay not promptly to leptonic final states but to unstable particles around the GC We assume that this unstable particle has a sufficiently long life time to propagate a large enough distance from the GC and decay to electron-positron pair(s) potentially with other particles near the Earth. Safe from the bound reported by the Fermi-LAT Collaboration [34] in the sense that our process is topologically similar to the one that the ordinary DM pair annihilates to a pair of muons, followed by their three-body decay Another important issue in realizing our mechanism is to secure an enough ψ flux near the Earth for explaining the positron bump reported by AMS-02. Reflecting this uncertainness, we shall treat the core size and the DM density inside the core as free parameters in our data analysis
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