Large-angle cosmic microwave background anisotropy in an open universe in the one-bubble inflationary scenario

We consider an alternative scenario of inflation which can account for a spatially open universe. It is similar to the old inflation in which the bubble nucleation occurs in the sea of the false vacuum, but it differs from the old inflation in that the second slow rollover inflation occurs inside a nucleated bubble. Hence, our observable universe is entirely contained in one nucleated bubble. The significance of the scenario is that apart from a variance caused by model parameters, it gives us a definite prediction on the spectrum of the primordial density perturbations, and hence it is observationally testable. Here we investigate the spectrum of cosmic microwave background anisotropies on large angular scales. We find that the contribution from peculiar modes which never appear in the usual harmonic analysis is significant in the case Ω₀ ≲ 0.1.