SMALL-SCALE COSMIC MICROWAVE BACKGROUND ANISOTROPIES AS A PROBE OF THE GEOMETRY OF THE UNIVERSE

We perform detailed calculations of cosmic microwave background (CMB) anisotropies in a CDM-dominated open universe with primordial adiabati c density perturbations for a variety of reionization histories. The C MB anisotropies depend primarily on the geometry of the universe, whic h in a matter-dominated universe is determined by OMEGA, and the optic al depth to the surface of last scattering. In particular, the locatio n of the primary Doppler peak depends primarily on OMEGA and is fairly insensitive to the other unknown parameters, such as OMEGA(b), h, LAM BDA, and the shape of the power spectrum. Therefore, if the primordial density perturbations are adiabatic, measurements of CMB anisotropies on small scales may be used to determine OMEGA.