X-ray Cluster Cosmology
  Sensitive, wide-area X-ray surveys which would be possible with the WFXT will
detect huge samples of virialized objects spanning the mass range from
sub-groups to the most massive clusters, and extending in redshift to beyond
z=2. These samples will be an excellent dataset for carrying out many
traditional cosmological tests using the cluster mass function and power
spectrum. Uniquely, WFXT will be able not only to detect clusters but also to
make detailed X-ray measurements for a large number of clusters and groups
right from the survey data. Very high quality measurements of the cluster mass
function and spatial correlation over a very wide range of masses, spatial
scales, and redshifts, will be useful for expanding the cosmological discovery
space, and in particular, in searching for departures from the "concordant"
Lambda-CDM cosmological model. Finding such departures would have far-reaching
implications on our understanding of the fundamental physics which governs the
Universe.
