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 ΛCDM model at 3.7σ, and implies a sum of neutrino masses \sum m_ν= 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 ΛCDM model with no massive neutrinos (1.7σ), 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" (<2σ) between CMB and BAO+H_0 data will decrease as the uncertainties in these measurements decrease.