Quantum backreaction in string theory

TL;DR

This paper reviews how finite string quanta can cause significant backreaction effects in string theory, challenging traditional fixed-background approaches, with examples like D0-brane recoil and compact universe evolution.

Contribution

It provides a review of solved problems and current research on quantum backreaction effects in string theory, highlighting the need for amended formulations.

Findings

D0-brane recoil causes infrared divergences

Backreaction impacts evolution of compact universes

Current investigations address these backreaction effects

Abstract

There are situations in string theory when a finite number of string quanta induce a significant backreaction upon the background and render the perturbation theory infrared-divergent. The simplest example is D0-brane recoil under an impact by closed strings. A more physically interesting case is backreaction on the evolution of a totally compact universe due to closed string gas. Such situations necessitate qualitative amendments to the traditional formulation of string theory in a fixed classical background. In this contribution to the proceedings of the XVII European Workshop on String Theory in Padua, I review solved problems and current investigations in relation to this kind of quantum backreaction effects.