Superstrings on Curved Spacetimes

TL;DR

This paper reviews recent advances in understanding superstrings in curved spacetimes, focusing on exact conformal field theories, their geometries, dualities, and quantum properties, with applications to black holes and singularities.

Contribution

It provides a complete classification of gauged Wess-Zumino-Witten models for all dimensions and constructs heterotic superstring models in curved backgrounds based on non-compact groups.

Findings

Exact conformal field theories for gravitational backgrounds identified

Classical and quantum geometries of models analyzed

Large-small duality properties reformulated as group space inversion

Abstract

In this lecture I summarize recent developments on strings propagating in curved spacetime. Exact conformal field theories that describe gravitational backgrounds such as black holes and more intricate gravitational singularities have been discovered and investigated at the classical and quantum level. These models are described by gauged Wess-Zumino-Witten models, or equivalently current algebra G/H coset models based on non-compact groups, with a single time coordinate. The classification of such models for all dimensions is complete. Furthermore the heterotic superstrings in curved spacetime based on non-compact groups have also been constructed. For many of the $d\le 4$ models the gravitational geometry described by a sigma model has been determined. Some general results outlined here include a global analysis of the geometry and the exact classical geodesics for any G/H model. Moreover, in the quantized theory, the conformally exact metric and dilaton are obtained for all orders in an expansion of $k$ (the central extension). All such models have large-small (or mirror) duality properties which we reformulate as an inversion in group space. To illustrate model building techniques a specific 4-dimensional heterotic string in curved spacetime is presented. Finally the methods for investigating the quantum theory are outlined. The construction and analysis of these models at the classical and quantum level involve some aspects of noncompact groups which are not yet sufficiently well understood. Some of the open problems in the physics and mathematics areas are outlined.