On the modularity of certain functions from the Gromov-Witten theory of elliptic orbifolds

Abstract: In this paper, we study modularity of several functions which naturally arose in a paper of Lau and Zhou on open Gromov-Witten potentials of elliptic orbifolds. They derived a number of examples of indefinite theta functions, and we provide modular completions for several such functions which involve more complicated objects than ordinary modular forms. In particular, we give new closed formulas for special indefinite theta functions of type $(1,2)$ in terms of products of mock modular forms. This formula is also of independent interest.