Theta integrals and generalized error functions

TL;DR

This paper links generalized error functions and indefinite theta series of signature (n-2,2) to integrals of theta series over certain surfaces, providing new geometric interpretations and modular properties.

Contribution

It demonstrates that ABMP-indefinite theta series can be realized as integrals of theta series over specific surfaces, extending previous constructions and interpretations.

Findings

ABMP-indefinite theta series expressed as integrals over surfaces

The associated q-series as generating functions for intersection numbers

Connection between theta series, geometry, and modular forms

Abstract

In a recent preprint, arXiv:1606.05495v1, Alexandrov, Banerjee, Manschot and Pioline introduced generalized error functions and used them to construct indefinite theta series associated to quadratic lattices L of signature (n-2,2). These series are generalizations of those constructed by Zwegers for lattices of signature (n-1,1) and are shown to be `modular completions' of certain nice $q$-series. In this paper, we show that the ABMP-indefinite theta series for signature (n-2,2) can also be obtained as integrals of the form valued theta series introduced in joint work with J. Millson in 1986. Given two pairs {C1,C2} and {C2,C2'} of negative vectors in the real quadratic space V obtained from L, we suppose that these vectors determine 4 distinct oriented negative 2-planes {C1,C2},{C1,C2'},{C1',C2'},{C1',C2} lying in the same component of the space D of oriented negative 2 -planes in V. These 2-planes determined a surface S in D and the non-holomorphic modular form obtained by integrating the KM-theta series over S is show to coincide with the ABMP-indefinite theta series. Moreover, the associated q-series in interpreted as the generating series for the intersection numbers of S with the codimension 2 subspaces D_x of D defined by positive lattice vectors.