Off-shell tachyon amplitudes: analyticity and projective invariance

TL;DR

This paper computes off-shell tachyon amplitudes in string theory, demonstrating that the four-tachyon amplitude maintains the same analyticity properties as the on-shell case, using projective invariance.

Contribution

It introduces a method to compute off-shell tachyon amplitudes that preserves analyticity and projective invariance, extending previous on-shell results to off-shell scenarios.

Findings

Off-shell four-tachyon amplitude matches on-shell analyticity properties.

Method applies to both bosonic and fermionic strings.

Results extend to type 0 string theory.

Abstract

We compute off-shell three- and four-tachyon amplitudes at tree level by using a prescription based on the requirement of projective invariance. In particular we show that the off-shell four-tachyon amplitude can be put in the same form as the corresponding on-shell one, exhibiting therefore the same analyticity properties. This is shown both for the bosonic and the fermionic string. The result obtained in the latter case can be extended to the off-shell four-tachyon amplitude in type 0 theory.