Global Structure of Deffayet (Dvali-Gabadadze-Porrati) Cosmologies

TL;DR

This paper explores the five-dimensional bulk structure of Dvali-Gabadadze-Porrati cosmologies, revealing how bulk geometry influences brane universe evolution, causality, and perturbation behavior.

Contribution

It provides a detailed framework for understanding the global bulk structure and its impact on cosmological phenomena in DGP braneworld models.

Findings

Bulk observer sees the brane as an expanding bubble

Shortcuts through the bulk can cause apparent causality violations

Large-scale metric perturbations show power depletion

Abstract

We detail the global structure of the five-dimensional bulk for the cosmological evolution of Dvali-Gabadadze-Porrati braneworlds. The picture articulated here provides a framework and intuition for understanding how metric perturbations leave (and possibly reenter) the brane universe. A bulk observer sees the braneworld as a relativistically expanding bubble, viewed either from the interior (in the case of the Friedmann-Lemaitre-Robertson-Walker phase) or the exterior (the self-accelerating phase). Shortcuts through the bulk in the first phase can lead to an apparent brane causality violation and provide an opportunity for the evasion of the horizon problem found in conventional four-dimensional cosmologies. Features of the global geometry in the latter phase anticipate a depletion of power for linear metric perturbations on large scales.