  The X-ray emission from clusters of galaxies is one of the most pursued
observational probe to investigate the distribution of dark matter and the
related density parameter Omega0. The crucial link to derive the statistics of
observables from a dynamical theory is constituted by the physics for the
diffuse baryons (or ICP) responsible of the X-ray emission. Here we present a
physical model for the ICP which leads to a definite L-T relation. Then we
perform a physically based cosmological test, pointing out three cold dark
matter universes: a Tilted critical CDM, a flat CDM with Omega0=0.3, and an
Open CDM with Omega0=0.5, which are discussed on the basis of the RDCS survey.
