Non-Gaussian Distribution and Clustering of Hot and Cold Pixels in the
  WMAP Five-Year Sky
  We present measurements of the clustering of hot and cold patches in the
microwave background sky as measured from the Wilkinson Microwave Anisotropy
Probe (WMAP) five-year data. These measurements are compared with theoretical
predictions which assume that the cosmological signal obeys Gaussian
statistics. We find significant differences from the simplest Gaussian-based
prediction. However, the measurements are sensitive to the fact that the noise
is spatially inhomogeneous (e.g., because different parts of the sky were
observed for different lengths of time). We show how to account for this
spatial inhomogeneity when making predictions. Differences from the
Gaussian-based expectation remain even after this more careful accounting of
the noise. In particular, we note that hot and cold pixels cluster differently
within the same temperature thresholds at few-degree scales. While these
findings may indicate primordial non-Gaussianity, we discuss other plausible
explanations for these discrepancies. In addition, we find some deviations from
Gaussianity at sub-degree scales, especially in the W band, whose origin may be
associated with extragalactic dust emission.
