Stringy Bubbles Solve de Sitter Troubles

Tristan Hübsch,Djordje Minic,Per Berglund

doi:10.3390/universe7100363

Tristan Hübsch, Djordje Minic + Show 1 more

Open Access

https://doi.org/10.3390/universe7100363

Copy DOI

Abstract

Finding four-dimensional de Sitter spacetime solutions in string theory has been a vexing quest ever since the discovery of the accelerating expansion of the universe. Building on a recent analysis of bubble-nucleation in the decay of (false-vacuum) AdS backgrounds where the interfacing bubbles themselves exhibit a de Sitter geometry we show that this resonates strongly with a stringy cosmic brane construction that naturally provides for an exponential mass-hierarchy and the localization of both gravity and matter, in addition to an exponentially suppressed positive cosmological constant. Finally, we argue that these scenarios can be realized in terms of a generalization of a small resolution of a conifold singularity in the context of a (Lorentzian) Calabi–Yau 5-fold, where the isolated (Lorentzian) two complex dimensional Fano variety is a four-dimensional de Sitter spacetime.

Highlights

For almost a quarter of a century, a specter has been haunting string theory: the accelerated expansion of our universe implies an asymptotically and approximately de Sitter geometry with a small but positive cosmological constant [1,2]
Recent work [6,7,8], as well as [9], turn out to correspond naturally with a stringy cosmic de Sitter (dS)-brane toy-model [10,11,12,13,14,15], which we connect with a generalization of the proposal that allows for more general spacetime varying string vacua [16]
The global geometry of the ten-dimensional spacetime is reviewed in Section 4, where we present evidence that the most generic of spacetime geometries in string theory necessarily include exceptional four-dimensional sub-spacetimes of positive curvature, the simplest of which being dS1,3

Summary

Introduction

For almost a quarter of a century, a specter has been haunting string theory: the accelerated expansion of our universe implies an asymptotically and approximately de Sitter (dS) geometry with a small but positive cosmological constant [1,2]. Constructing solutions in string theory with these features has been argued to be notoriously hard if not impossible: see [3,4,5] for recent comprehensive reviews. This in turn lets us modify the former so as to afford a dynamical scenario akin to the latter. The global geometry of the ten-dimensional spacetime is reviewed, where we present evidence that the most generic of spacetime geometries in string theory necessarily include exceptional four-dimensional sub-spacetimes of positive curvature, the simplest of which being dS1,3.

Nearly Singular Spacetimes

Warped Deformed Conifolds and Alike

A Discretuum of Toy Models

Calabi–Yau 5-Folds

Summary, Outlook and Conclusions