Modular forms for three-loop banana integrals

TL;DR

This paper investigates the automorphic properties of periods of K3 surfaces related to three-loop banana Feynman integrals, revealing their connection to various types of modular forms depending on mass configurations.

Contribution

It demonstrates how periods of K3 surfaces associated with three-loop banana integrals can be expressed as different classes of modular forms, using exceptional isomorphisms and intersection products.

Findings

Maximal cuts correspond to ordinary, Hilbert, Siegel, or hermitian modular forms.

Periods can be expressed in terms of well-studied mathematical modular forms.

Automorphic properties help classify Feynman integral cuts in terms of modular forms.

Abstract

We study periods of multi-parameter families of K3 surfaces, which are relevant to compute the maximal cuts of certain classes of Feynman integrals. We focus on their automorphic properties, and we show that generically the periods define orthogonal modular forms. Using exceptional isomorphisms between Lie groups of small rank, we show how one can use the intersection product on the periods to identify K3 surfaces whose periods can be expressed in terms of other classes of modular forms that have been studied in the mathematics literature. We apply our results to maximal cuts of three-loop banana integrals, and we show that depending on the mass configuration, the maximal cuts define ordinary modular forms or Hilbert, Siegel or hermitian modular forms.