New constraint on open cold-dark-matter models

We calculate the large-angle cross correlation between the cosmic-microwave -background temperature and the x-ray-background intensity expected in an o pen universe with cold dark matter (CDM) and a nearly scale-invariant spect rum of adiabatic density perturbations. Results are presented as a function of the nonrelativistic-matter density Omega(0) and the x-ray bias b(x) for both an open universe and a flat cosmological-constant universe. Recent ex perimental upper limits to the amplitude of this cross correlation provide a new constraint to the Omega(0)-b(x) parameter space that open-CDM models (and the open-inflation models that produce them) must satisfy. [S0031-9007 (99)09256-X].