The Feynman $i ε$ in String Theory

Abstract

The Feynman $i\varepsilon$ is an important ingredient in defining perturbative scattering amplitudes in field theory. Here we describe its analog in string theory. Roughly one takes the string worldsheet to have Lorentz signature when a string is going on-shell although it has Euclidean signature generically.

24 pp.This article is based on a talk presented at the Zuminofest in Berkeley, California, May 2-4, 2013