Accelerating universes and string theory

Accelerating Universes and String Theory

This article reviews recent developments in the study of universes with a positive cosmological constant in string theory. 1. The Challenge of Time It is evident that the world around us changes in time. At cosmological scales there is strong evidence that the universe was much hotter and denser some 13 billion years ago and has expanded and cooled since then, probably even undergoing an early ...

Gödel Universes in String Theory

We show that homogeneous Gödel spacetimes need not contain closed timelike curves in low-energy-effective string theories. We find exact solutions for the Gödel metric in string theory for the full O(α) action including both dilaton and axion fields. The results are valid for bosonic, heterotic and super-strings. To first order in the inverse string tension α, these solutions display a simple r...

Baby universes in string theory

Robbert Dijkgraaf, Rajesh Gopakumar, Hirosi Ooguri, and Cumrun Vafa Institute for Theoretical Physics & KdV Institute for Mathematics, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India California Institute for Technology, 452-48, Pasadena, California 91125, USA Jefferson Physical Labo...

Supersymmetric Gödel Universes in String Theory

Supersymmetric backgrounds in string and M-theory of the Gödel Universe type are studied. We find several new Gödel Universes that preserve up to 20 supersymmetries. In particular, we obtain an interesting Gödel Universe in M-theory with 18 supersymmetries which does not seem to be dual to a pp-wave. We show that not only T-duality but also the typeIIA/M-theory S-duality can give supersymmetric...

Complex geometry and vacua: Counting universes in string theory