  We investigate the feasibility of the indirect detection of dark matter in a
simple model using the neutrino portal. The model is very economical, with
right-handed neutrinos generating neutrino masses through the Type-I seesaw
mechanism and simultaneously mediating interactions with dark matter. Given the
small neutrino Yukawa couplings expected in a Type-I seesaw, direct detection
and accelerator probes of dark matter in this scenario are challenging.
However, dark matter can efficiently annihilate to right-handed neutrinos,
which then decay via active-sterile mixing through the weak interactions,
leading to a variety of indirect astronomical signatures. We derive the
existing constraints on this scenario from Planck cosmic microwave background
measurements, Fermi dwarf spheroidal galaxies and Galactic Center gamma-rays
observations, and Alpha Magnetic Spectrometer - 02 antiprotons observations,
and also discuss the future prospects of Fermi and the Cherenkov Telescope
Array. Thermal annihilation rates are already being probed for dark matter
lighter than about 50 GeV, and this can be extended to dark matter masses of
100 GeV and beyond in the future. This scenario can also provide a dark matter
interpretation of the Fermi Galactic Center gamma ray excess, and we confront
this interpretation with other indirect constraints. Finally we discuss some of
the exciting implications of extensions of the minimal model with large
neutrino Yukawa couplings and Higgs portal couplings.
