The Overall Coefficient of the Two-loop Superstring Amplitude Using Pure Spinors

TL;DR

This paper calculates the two-loop four-point amplitude coefficient in superstring theory using pure spinor formalism, providing a direct and smooth computation method that overcomes previous normalization challenges.

Contribution

It introduces a first-principles calculation of the superstring amplitude coefficient using pure spinor superspace integrals, avoiding the normalization issues of earlier formalisms.

Findings

Successful direct computation of the two-loop amplitude coefficient

Demonstration of the pure spinor formalism's computational advantages

Clarification of normalization issues in superstring amplitude calculations

Abstract

Using the results recently obtained for computing integrals over (non-minimal) pure spinor superspace, we compute the coefficient of the massless two-loop four-point amplitude from first principles. Contrasting with the mathematical difficulties in the RNS formalism where unknown normalizations of chiral determinant formulae force the two-loop coefficient to be determined only indirectly through factorization, the computation in the pure spinor formalism can be smoothly carried out.