A note on on-shell recursion relation of string amplitudes

TL;DR

This paper addresses the challenge of summing infinite intermediate states in on-shell recursion relations for string amplitudes by including unphysical states to complete the Fock space.

Contribution

It introduces a method to explicitly sum over infinite string states by incorporating unphysical states, enhancing the on-shell recursion approach.

Findings

Explicit summation over infinite states achieved

Unphysical states inclusion simplifies calculations

Method improves recursion relation applications

Abstract

In the application of on-shell recursion relation to string amplitudes, one challenge is the sum over infinite intermediate on-shell string states. In this note, we show how to sum these infinite states explicitly by including unphysical states to make complete Fock space.