Imprint ofΩon the Cosmic Microwave Background

We investigate the dependence of large-angular-scale cosmic microwave background anisotropies on various initial conditions, including both adiabatic and isocurvature perturbations and the initial power-law index $n$, in a variety of low-$\Omega$ cosmological models. $\Lambda$-dominated flat models, inflationary open adiabatic models, with $n_{\mathrm{eff}}<1\mathrm{}$, and open isocurvature models, with $n_{\mathrm{eff}}\simeq 2$, are significantly constrained.