Off-shell amplitudes for nonoriented closed strings

TL;DR

This paper derives a simple operator-based expression for off-shell amplitudes involving multiple massless states on the Klein bottle in bosonic closed string theory.

Contribution

It provides a novel, straightforward formulation of off-shell amplitudes for nonoriented closed strings using the operator formalism.

Findings

Explicit off-shell amplitude expression for massless states on the Klein bottle

Simplifies calculations in bosonic closed string theory

Facilitates further theoretical developments in string amplitudes

Abstract

In the context of the bosonic closed string theory, by using the operatorial formalism, we give a simple expression of the off-shell amplitude with an arbitrary number of external massless states inserted on the Klein bottle.