Bouncing Brane Cosmologies from Warped String Compactifications

TL;DR

This paper explores how a brane in a warped string compactification can induce a bouncing cosmology, providing a string theory resolution to spacelike singularities through a scalar-tensor gravity framework.

Contribution

It demonstrates that warped deformed conifold geometries can produce non-singular bouncing universes in string theory, with a classical violation of the null energy condition enabling the bounce.

Findings

The brane cosmology is a smooth bounce from contraction to expansion.

Warped deformed conifold resolves big crunch singularity.

Effective 4D theory is a scalar-tensor gravity model.

Abstract

We study the cosmology induced on a brane probing a warped throat region in a Calabi-Yau compactification of type IIB string theory. For the case of a BPS D3-brane probing the Klebanov-Strassler warped deformed conifold, the cosmology described by a suitable brane observer is a bouncing, spatially flat Friedmann-Robertson-Walker universe with time-varying Newton's constant, which passes smoothly from a contracting to an expanding phase. In the Klebanov-Tseytlin approximation to the Klebanov-Strassler solution the cosmology would end with a big crunch singularity. In this sense, the warped deformed conifold provides a string theory resolution of a spacelike singularity in the brane cosmology. The four-dimensional effective action appropriate for a brane observer is a simple scalar-tensor theory of gravity. In this description of the physics, a bounce is possible because the relevant energy-momentum tensor can classically violate the null energy condition.