String field theory in curved spacetime and the resolution of spacelike singularities

TL;DR

This work targets the problem of spacelike singularities in general relativity by leveraging string theory to compute the quantum stress tensor of string matter in a fixed curved background, using a minisuperspace approach to model the singular region via homogeneous anisotropic metrics and dilaton dynamics.By analyzing large-string dynamics in expanding backgrounds and employing L0 Virasoro constraints alongside adiabatic and semiclassical limits, the authors derive a universal exponential suppression factor for string production per mode, leading to a total production that can diverge when the expansion rate reaches the string scale, i.e., near ρ_c ≈ 2π/(c√α′).The central finding is that fixed-background string production yields either a phase transition or substantial backreaction that could slow or avert the singularity; this motivates incorporating macroscopic string sources into β-function equations and points to the necessity of a more complete, potentially background-independent quantum gravity description to resolve spacelike singularities.Overall, the paper highlights a potentially fundamental interplay between string-scale physics and spacetime evolution, with implications for black hole interiors and the viability of singularity theorems in a quantum string-theoretic setting.

Abstract

We attempt to understand the fate of spacelike gravitational singularities in string theory via the quantum stress tensor for string matter in a fixed background. We first approximate the singularity with a homogeneous anisotropic background and review the minisuperspace equations describing the evolution of the scale factors and the dilaton. We then review and discuss the behavior of large strings in such models. In a simple model which expands isotropically for a finite period of time we compute the number density of strings produced by quantum pair production and find that this number, and thus the stress tensor, becomes infinite when the Hubble volume of the expansion exceeds the string scale, in a manner reminiscent of the Hagedorn transition. Based on this calculation we argue that either the region near the singularity undergoes a phase transition when the density reaches the order of a string mass per string volume, or that the backreaction of the produced string matter dramatically modifies the geometry.