There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
We assess two potential signals of the formation of our universe by the decay of a
false vacuum. Negative spatial curvature is one possibility, but the window for its
detection is now small. However, another possible signal is a suppression of the CMB
power spectrum at large angles. This arises from the steepening of the effective potential
as it interpolates between a flat inflationary plateau and the high barrier separating
us from our parent vacuum. We demonstrate that these two effects can be parametrically
separated in angular scale.
Observationally, the steepening effect appears to be excluded at large l; but it remains
consistent with the slight lack of power below l about 30 found by the WMAP and Planck
collaborations. We give two simple models which improve the fit to the Planck data;
one with observable curvature and one without. Despite cosmic variance, we argue that
future CMB polarization and most importantly large-scale structure observations should
be able to corroborate the Planck anomaly if it is real.
If we further assume the specific theoretical setting of a landscape of metastable
vacua, as suggested by string theory, we can estimate the probability of seeing a
low-l suppression in the CMB. There are significant theoretical uncertainties in such
calculations, but we argue the probability for a detectable suppression may be as
large as O(1), and in general is significantly larger than the probability of seeing
curvature.