Hidden-sector dark matter achieves standard thermal relic abundance via early decoupling with temperature-matched freeze-out, enabling WIMP-like cross sections without late-time thermalization.
Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
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abstract
We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10 degrees around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25 degrees and 10 degrees from the Galactic Center is well described by a the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25 degrees (~175 parsecs) of the Galactic Center, in contrast, departs from the expectations for by these processes. Instead, we find an additional component of gamma ray emission that is highly concentrated around the Galactic Center. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution (density proportional to r^{-gamma}, with gamma=1.18 to 1.33). The observed spectrum of this component, which peaks at energies between 1-4 GeV (in E^2 units), can be well fit by a 7-10 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of 4.6 x 10^-27 to 5.3 x 10^-26 cm^3/s, depending on how the dark matter distribution is normalized. We also discuss other sources for this emission, including the possibility that much of it originates from the Milky Way's supermassive black hole.
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Cosmic ray protons scattering off dark matter produce the Galactic Center gamma-ray excess through inelastic up-scattering followed by decay or direct elastic 2-to-3 photon production.
Paleo-detectors can achieve high sensitivity to sub-GeV dark matter boosted by cosmic rays and supernovae, covering previously inaccessible parameter space with orders of magnitude better reach than current experiments.
Joint prompt and inverse-Compton modeling of MSP-injected e± yields strong upper limits on η_e/η_γ from recent Fermi-LAT GCE spectra that exceed MAGIC globular-cluster bounds.
An optimized Fermi-LAT analysis finds the Galactic Center Excess follows an approximately spherical generalized NFW morphology with inner slope ~1.15, a spectrum peaking at a few GeV, and only upper limits above tens of GeV.
WIMP models for the Galactic Center Excess survive only in finely tuned resonant funnels with portal couplings around 10^-4, with leptophilic vectors and pseudoscalar portals remaining most viable after current bounds.
Projects COSI and AMEGO-X sensitivities to sub-GeV DM in vector-scalar portals, finding COSI leading in some regions beyond CMB limits and AMEGO-X covering most continuum cases.