Two-loop scalar diagrams from string theory

TL;DR

This paper derives two-loop scalar Feynman diagrams for $\

Contribution

It introduces a method to obtain normalized $\

Findings

Explicit two-loop $\

Preparation for multiloop non-abelian gauge theory amplitudes.

Abstract

We show how to obtain correctly normalized expressions for the Feynman diagrams of $\Phi^3$ theory with an internal $U(N)$ symmetry group, starting from tachyon amplitudes of the open bosonic string, and suitably performing the zero--slope limit by giving an arbitrary mass $m$ to the tachyon. In particular we present explicit results for the two--loop amplitudes of $\Phi^3$ theory, in preparation for the more interesting case of the multiloop amplitudes of non--abelian gauge theories.