Abstract

We investigate one-loop four-point scattering of non-abelian gauge bosons in heterotic string theory and identify new connections with the corresponding open-string amplitude. In the low-energy expansion of the heterotic-string amplitude, the integrals over torus punctures are systematically evaluated in terms of modular graph forms, certain non-holomorphic modular forms. For a specific torus integral, the modular graph forms in the low-energy expansion are related to the elliptic multiple zeta values from the analogous open-string integrations over cylinder boundaries. The detailed correspondence between these modular graph forms and elliptic multiple zeta values supports a recent proposal for an elliptic generalization of the single-valued map at genus zero.

Highlights

  • Scattering amplitudes in string theories have become a rewarding laboratory to encounter modern number-theoretic concepts in a simple setup

  • We investigate one-loop four-point scattering of non-abelian gauge bosons in heterotic string theory and identify new connections with the corresponding open-string amplitude

  • The detailed correspondence between these modular graph forms and elliptic multiple zeta values supports a recent proposal for an elliptic generalization of the single-valued map at genus zero

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Summary

Introduction

Scattering amplitudes in string theories have become a rewarding laboratory to encounter modern number-theoretic concepts in a simple setup. By comparing the eMZVs and modular graph functions in one-loop amplitudes of open and closed strings, a conjecture for the explicit form of an elliptic singlevalued map has been made in [22]. Given that the heterotic string relaxes the maximal supersymmetry of type-II superstrings, its extended set of moduli-space integrals (as investigated here at four points) is hoped to give a more general picture of an elliptic single-valued map As another consequence of the half-maximal supersymmetry of the heterotic string, the coefficients of a given modular graph form in massless one-loop amplitudes usually mix different orders in α. Relating an integral of modular weight (2, 0) in the four-point gauge amplitude of the heterotic string to a cylinder integral of the open superstring by applying the tentative elliptic single-valued map of [22] order by order in the α -expansion. Several technical details needed in the analysis have been relegated to a number of appendices

Kronecker-Eisenstein series and elliptic functions
One-loop gauge amplitudes of the heterotic string
Spin-summed current correlators
The key integrals over torus punctures
Modular graph functions
Modular graph forms
Relations among modular graph forms
Holomorphic subgraph reduction
Trihedral modular graph forms
Modular properties
Differential equations and iterated Eisenstein integrals
Cauchy-Riemann derivatives of modular graph forms
Iterated Eisenstein integrals
Fourier expansion of the Vw functions
Heterotic graph forms
Planar heterotic graph forms
Leading orders α 0 and α 1
Subleading orders α 2 and α 3
Non-planar heterotic graph forms
Assembling the results
Uniform transcendentality and α -expansions
The planar results in terms of uniform-transcendentality integrals
The non-planar results in terms of uniform-transcendentality integrals
The integrated amplitude and the low-energy effective action
Planar amplitude up to second order in α
Non-planar amplitude up to second order in α
Consistency with tree-level amplitudes
Modular graph forms in the massless n-point function
Adjoining external gravitons
Heterotic strings versus open superstrings
The closed-string expansion in terms of iterated Eisenstein integrals
Findings
Conclusions
Full Text
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