On the Rankin-Selberg method for higher genus string amplitudes

TL;DR

This paper extends the Rankin-Selberg method to higher genus string amplitudes involving Siegel modular functions with polynomial growth, enabling the computation of integrals related to string theory partition functions.

Contribution

It generalizes Zagier's Rankin-Selberg extension to genus 2 and 3, providing a framework for renormalized integrals with polynomial growth near cusps.

Findings

Renormalized integrals relate to residues of Langlands-Eisenstein series.

Method applies to Siegel-Narain partition functions of self-dual lattices.

Establishes a link between string amplitudes and automorphic forms.

Abstract

Closed string amplitudes at genus $h\leq 3$ are given by integrals of Siegel modular functions on a fundamental domain of the Siegel upper half-plane. When the integrand is of rapid decay near the cusps, the integral can be computed by the Rankin-Selberg method, which consists of inserting an Eisenstein series $E_h(s)$ in the integrand, computing the integral by the orbit method, and finally extracting the residue at a suitable value of $s$. String amplitudes, however, typically involve integrands with polynomial or even exponential growth at the cusps, and a renormalization scheme is required to treat infrared divergences. Generalizing Zagier's extension of the Rankin-Selberg method at genus one, we develop the Rankin-Selberg method for Siegel modular functions of degree 2 and 3 with polynomial growth near the cusps. In particular, we show that the renormalized modular integral of the Siegel-Narain partition function of an even self-dual lattice of signature $(d,d)$ is proportional to a residue of the Langlands-Eisenstein series attached to the $h$-th antisymmetric tensor representation of the T-duality group $O(d,d,Z)$.