The String Light Cone in the pp-wave Background

TL;DR

This paper derives the particle and string light cones in the pp-wave background, revealing a periodic structure in light cone time and implications for the consistency of quantum theories in such backgrounds.

Contribution

It provides the first explicit determination of the light cone structure in the pp-wave background, showing a periodicity that influences quantum theory formulation.

Findings

Light cone is a deformed version of flat space

Light cone exhibits periodicity in light cone time x^+

Quantum theory in pp-wave background requires periodicity in x^+

Abstract

In this letter, we determine the particle and the string light cone in the pp-wave background. The result is a deformed version of the flat one. We point out the light cone exhibits an intriguing periodicity in the light cone time direction x^+ with a period \sim 1/ \mu. Our results also suggest that a quantum theory in the pp-wave background can be formulated consistently only if the background is periodic in the light cone time x^+.