  Data from 105 days from the High Altitude Water Cherenkov Observatory (HAWC)
have been used to place a new limit on an isotropic diffuse gamma-ray
population above 10 TeV. High- energy isotropic diffuse gamma-ray emission is
produced by unresolved extragalactic objects such as active galactic nuclei,
with potential contributions from interactions of high-energy cosmic rays with
the inter-Galactic medium, or dark matter annihilation. Isotropic diffuse
gamma-ray emission has been observed up to nearly 1 TeV. Above this energy,
only upper limits have been reported. Observations or limits of the isotropic
photon population above these energies are very sensitive to local
astrophysical particle production. Of particular note, we expect a photon
population to accompany the TeV-PeV astrophysical neutrino detection seen in
the IceCube instrument. Observations or limits of a photon population above
this energy can point to the origin of these neutrinos, indicating whether they
are within the gamma-ray horizon or not. HAWC, with superior sensitivity to
gamma rays between 100 GeV and 100 TeV, continuously observes the overhead sky
and will measure or constrain isotropic emission above 1 TeV. We present a
limit above 10 TeV based on the background rejection achieved in a 105-day
observation of the Crab Nebula with HAWC. The limit will improve substantially
with additional data and study.
