Estimating f_NL and g_NL from Massive High-Redshift Galaxy Clusters
  There are observations of 15 high-redshift massive galaxy clusters, which
have an extremely small probability with a purely Gaussian initial curvature
perturbation. Here we revisit the estimation of the contribution of
non-Gaussianities to the cluster mass function and point out serious problems
that have resulted in the application of the mass function out of the range of
its validity. We remedy the situation and show that the values of f_NL
previously claimed to completely reconcile (i.e. at ~100% confidence) the
existence of the clusters with LambdaCDM are unphysically small. However, for
WMAP cosmology and at 95% confidence, we arrive at the limit f_NL>411, which is
similar to previous estimates. We also explore the possibility of a large g_NL
as the reason for the observed excess of the massive galaxy clusters. This
scenario, g_NL>2*10^6, appears to be in more agreement with CMB and LSS limits
for the non-Gaussianity parameters and could also provide an explanation for
the overabundance of large voids in the early universe.
