Statistical diagnostics to identify Galactic foregrounds in B-mode maps
  Recent developments in the search for inflationary gravitational waves in the
cosmic microwave background (CMB) polarization motivate the search for new
diagnostics to distinguish the Galactic foreground contribution to B modes from
the cosmic signal. We show that B modes from these foregrounds should exhibit a
local hexadecapolar departure in power from statistical isotropy (SI). We
present a simple algorithm to search for a uniform SI violation of this sort,
as may arise in a sufficiently small patch of sky. We then show how to search
for these effects if the orientation of the SI violation varies across the
survey region, as is more likely to occur in surveys with more sky coverage. If
detected, these departures from Gaussianity would indicate some level of
Galactic foreground contamination in the B-mode maps. Given uncertainties about
foreground properties, though, caution should be exercised in attributing a
null detection to an absence of foregrounds.
