  We have performed an analysis of the diffuse gamma-ray emission with the
Fermi Large Area Telescope in the Milky Way Halo region searching for a signal
from dark matter annihilation or decay. In the absence of a robust dark matter
signal, constraints are presented. We consider both gamma rays produced
directly in the dark matter annihilation/decay and produced by inverse Compton
scattering of the e+e- produced in the annihilation/decay. Conservative limits
are derived requiring that the dark matter signal does not exceed the observed
diffuse gamma-ray emission. A second set of more stringent limits is derived
based on modeling the foreground astrophysical diffuse emission using the
GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the
distribution of the cosmic-ray sources in the Galaxy, the index of the
injection cosmic-ray electron spectrum and the column density of the
interstellar gas are taken into account using a profile likelihood formalism,
while the parameters governing the cosmic-ray propagation have been derived
from fits to local cosmic-ray data. The resulting limits impact the range of
particle masses over which dark matter thermal production in the early Universe
is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic
ray anomalies as annihilation of dark matter.
