Cambridge Journal of Mathematics

Volume 6 (2018)

Number 1

Indefinite theta functions arising in Gromov–Witten theory of elliptic orbifolds

Pages: 25 – 57



Kathrin Bringmann (Mathematical Institute, University of Cologne, Germany)

Jonas Kaszián (Mathematical Institute, University of Cologne, Germany)

Larry Rolen (Hamilton Mathematics Institute & School of Mathematics, Trinity College, Dublin, Ireland)


In this paper, we consider natural geometric objects coming from Lagrangian Floer theory and mirror symmetry. Lau and Zhou showed that some of the explicit Gromov-Witten potentials computed by Cho, Hong, Kim, and Lau are essentially classical modular forms. Recent work by Zwegers and two of the authors determined modularity properties of several simpler pieces of the last, and most mysterious, function by developing several identities between functions with properties generalizing those of the mock modular forms in Zwegers’ thesis. Here, we complete the analysis of all pieces of Cho, Hong, Kim, and Lau’s functions, inspired by recent work of Alexandrov, Banerjee, Manschot, and Pioline on similar functions. Combined with the work of Lau and Zhou, as well as the aforementioned work of Zwegers and two of the authors, this affords a complete understanding of the modularity transformation properties of the open Gromov-Witten potentials of elliptic orbifolds of the form $\mathbb{P}^1_{a,b,c}$ computed by Cho, Hong, Kim, and Lau. It is hoped that this will provide a fuller picture of the mirror-symmetric properties of these orbifolds in subsequent works.

The research of the first author is supported by the Alfried Krupp Prize for Young University Teachers of the Krupp foundation and the Collaborative Research Centre / Transregio on Symplectic Structures in Geometry, Algebra and Dynamics (CRC/TRR 191) of the German Research Foundation.

Received 17 February 2017

Published 27 March 2018