CPT Invariance of String Models in a Minkowski Background

TL;DR

This paper investigates the CPT symmetry properties of string theories in flat Minkowski space, proving invariance of the S-matrix and exploring related issues like spin-statistics connection.

Contribution

It introduces a world-sheet transformation definition of CPT and demonstrates the CPT invariance of string S-matrix elements in a Minkowski background.

Findings

Proves CPT invariance of string S-matrix in Minkowski space

Defines CPT as a world-sheet transformation on vertex operators

Explores the spin-statistics relation in string states

Abstract

We study the space-time CPT properties of string theories formulated in a flat Minkowski background of even dimension. We define CPT as a world-sheet transformation acting on the vertex operators and we prove the CPT invariance of the string $S$-matrix elements. Some related issues, including the connection between spin and statistics of physical string states, are also considered.