  The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide
field-of-view observatory sensitive to 500 GeV - 100 TeV gamma rays and cosmic
rays. With its observations over 2/3 of the sky every day, the HAWC observatory
is sensitive to a wide variety of astrophysical sources, including possible
gamma rays from dark matter. Dark matter annihilation and decay in the Milky
Way Galaxy should produce gamma-ray signals across many degrees on the sky. The
HAWC instantaneous field-of-view of 2 sr enables observations of extended
regions on the sky, such as those from dark matter in the Galactic halo. Here
we show limits on the dark matter annihilation cross-section and decay lifetime
from HAWC observations of the Galactic halo with 15 months of data. These are
some of the most robust limits on TeV and PeV dark matter, largely insensitive
to the dark matter morphology. These limits begin to constrain models in which
PeV IceCube neutrinos are explained by dark matter which primarily decays into
hadrons.
