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Zenith Grant Awardee

Hiranya V. Peiris

University College London


Matthew C. Johnson, Perimeter Institute for Theoretical Physics

Project Title

Detecting signatures of eternal inflation using WMAP and Planck data

Project Summary

Inflation, a postulated epoch of accelerated expansion in the early universe, has become a principal component of the standard model of cosmology. From a wide variety of initial conditions, inflation produces a nearly homogeneous universe populated by density fluctuations that seed large scale structure. However, inflation is such a good homogenizer that, once unleashed, it can become eternal, ending only inside of spontaneously nucleated bubbles. In this picture, our universe resides inside such a bubble, which could have formed from one of a huge variety of eternally inflating parent vacua. Is it possible to observationally verify the picture of eternal inflation, and determine the properties of the parent vacuum from which our observable universe formed? Surprisingly, the answer may be yes. The formation of our bubble, and the collision between bubbles, could leave characteristic signatures in the Cosmic Microwave Background (CMB). We propose to systematically search for these possible signatures of eternal inflation in data produced by the WMAP and Planck satellites, as well as address some outstanding theoretical questions regarding such signals.

Technical Abstract

This proposal aims to develop novel observational tests of the initial conditions for inflation. Theories with extra spatial dimensions, such as string theory, generically produce vast collections of lower dimensional vacua. In the presence of positive vacuum energy, such theories can give rise to the phenomenon of eternal inflation. In this picture, our observable universe is contained inside a bubble which was nucleated out of an eternally inflating parent vacuum, possibly with a different effective dimensionality. The goal of this proposal is to systematically search for signatures of eternal inflation in the Cosmic Microwave Background (CMB) data produced by the WMAP and Planck satellites, and to determine to what extent we can identify the properties of our parent vacuum. There are two classes of signatures we will consider: those arising from the formation of a single bubble universe, and those arising from the collision of bubble universes. We will focus first on search algorithms that rely only on generic properties and symmetries (e.g. azimuthal symmetry in bubble collisions) of various signatures. Simultaneously, we will investigate the theoretical properties of the two classes of signatures, developing more specific or model-dependent predictions, which can then be targeted in new search algorithms.

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