The Sunyaev-Zel'dovich Effect as a Probe of $\Omega_{o}$
  We examine how the Sunyaev-Zel'dovich (SZ) effect of clusters can probe $\Omega_{o}$. Using self-consistent models of X-ray clusters in the context of hierarchical models of structure formation, we show that both the mean Compton {\it y} parameter and the number of clusters observed via the SZ effect strongly depend on $\Omega_{o}$. These quantities are higher in open cosmological models due to the earlier epoch of structure formation. Specifically, we compare two models which are able to reproduce the present abundance of X-ray clusters, one for $\Omega_{o}=0.2$ and the other $\Omega = 1$. For $\Omega_{o}=0.2$, ${\ymean}$ exceeds the current FIRAS limit of $1.5\times10^{-5}$. Also, the SZ redshift source distribution considerably differs in the two cosmological models. Thus, these results show that both an improvement in our knowledge of CMB spectral distortions and the realization of millimeter surveys to look for SZ sources over a large area of the sky should produce interesting constraints on $\Omega_{o}$ and on the evolution of the baryonic fractionof virialized structures. 
Domingos Barbosa, James G. Bartlett, Alain Blanchard, Jamila Oukbir