String theory and the Classical Stability of Plane Waves

TL;DR

This paper investigates the classical stability of plane wave spacetimes in string theory, showing that despite tachyon-like modes, the type IIB vacuum plane wave remains perturbatively stable.

Contribution

It provides a perturbative stability analysis of the type IIB vacuum plane wave, addressing concerns about negative mass-squared modes.

Findings

The type IIB vacuum plane wave is perturbatively stable.

Negative mass-squared modes do not necessarily imply instability.

The analysis supports the consistency of plane wave backgrounds in string theory.

Abstract

The presence of fields with negative mass-squared typically leads to some form of instability in standard field theories. The observation that, at least in the light-cone gauge, strings propagating in plane wave spacetimes can have worldsheet scalars with such tachyon-like masses suggests that the supergravity background may itself be unstable. To address this issue, we perform a perturbative analysis around the type IIB vacuum plane wave, the solution which most obviously generates worldsheet scalars with negative mass-squared. We argue that this background is perturbatively stable.