Robust Likelihoods for Inflationary Gravitational Waves from Maps of
  Cosmic Microwave Background Polarization
  The B-mode polarization of the cosmic microwave background (CMB) provides a
unique window into tensor perturbations from inflationary gravitational waves.
Survey effects complicate the estimation and description of the power spectrum
on the largest angular scales. The pixel-space likelihood yields parameter
distributions without the power spectrum as an intermediate step, but it does
not have the large suite of tests available to power spectral methods. Searches
for primordial B-modes must rigorously reject and rule out contamination. Many
forms of contamination vary or are uncorrelated across epochs, frequencies,
surveys, or other data treatment subsets. The cross power and the power
spectrum of the difference of subset maps provide approaches to reject and
isolate excess variance. We develop an analogous joint pixel-space likelihood.
Contamination not modeled in the likelihood produces parameter-dependent bias
and complicates the interpretation of the difference map. We describe a null
test that consistently weights the difference map. Excess variance should
either be explicitly modeled in the covariance or be removed through
reprocessing the data.
