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 open universe with cold dark matter (CDM) and a nearly scale-invariant spectrum of adiabatic density perturbations. Results are presented as a function of the nonrelativistic-matter density Ω0 and the x-ray bias bx for both an open universe and a flat cosmological-constant universe. Recent experimental upper limits to the amplitude of this cross correlation provide a new constraint to the Ω0-bx parameter space that open-CDM models (and the open-inflation models that produce them) must satisfy.