Cluster Cosmology at a Crossroads: Neutrino Masses
  Galaxy clusters --- in combination with CMB and BAO data --- can provide
precise constraints on the sum of neutrino masses. However, these constraints
depend on the calibration of the mass--observable relation. For instance, the
mass calibration employed in Planck Collaboration (2011a,b) rules out the
minimal 6-parameter \Lambda CDM model at 3.7\sigma, and implies a sum of
neutrino masses \sum m_\nu = 0.39 \pm 0.10. By contrast, the mass calibration
favored by Rozo et al. (2012b) from a self-consistent analysis of X-ray, SZ,
and optical scaling relations is consistent with a minimal flat \Lambda CDM
model with no massive neutrinos (1.7\sigma), and is a better fit to additional
data (e.g. H0). We discuss these results in light of the recent SPT and ACT
analysis, noting that the Rozo et al. (2012b) model suggests the current mild
"tension" (<2\sigma) between CMB and BAO+H_0 data will decrease as the
uncertainties in these measurements decrease.
