Anisotropic Kantowski-Sachs Universe from Gravitational Tunneling and its Observational Signatures

TL;DR

This paper explores a model where our universe originated from a gravitational tunneling event involving decompactification, resulting in an anisotropic Kantowski-Sachs universe that could produce observable signatures in the CMB.

Contribution

It introduces a novel anisotropic universe model from gravitational tunneling with specific observational predictions for CMB anisotropies.

Findings

Predicts a quadrupolar power asymmetry in the CMB

Matches the sign and oscillations of WMAP anomalies

Amplitude of anisotropy is below current detection bounds

Abstract

In a landscape of compactifications with different numbers of macroscopic dimensions, it is possible that our universe has nucleated from a vacuum where some of our four large dimensions were compact while other, now compact, directions were macroscopic. From our perspective, this shapeshifting can be perceived as an anisotropic background spacetime. As an example, we present a model where our universe emerged from a tunneling event which involves the decompactification of two dimensions compactified on the two-sphere. In this case, our universe is of the Kantowski-Sachs type and therefore homogeneous and anisotropic. We study the deviations from statistical isotropy of the Cosmic Microwave Background induced by the anisotropic curvature, with particular attention to the anomalies. The model predicts a quadrupolar power asymmetry with the same sign and acoustic oscillations as found by WMAP. The amplitude of the effect is however too small given the current estimated bound on anisotropic curvature derived from the quadrupole.