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arXiv · 1702.05497

Multiple D3-instantons and mock modular forms II

Sergei Alexandrov·Sibasish Banerjee·Jan Manschot·Boris Pioline
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Abstract

We analyze the modular properties of D3-brane instanton corrections to the hypermultiplet moduli space in type IIB string theory compactified on a Calabi-Yau threefold. In Part I, we found a necessary condition for the existence of an isometric action of S-duality on this moduli space: the generating function of DT invariants in the large volume attractor chamber must be a vector-valued mock modular form with specified modular properties. In this work, we prove that this condition is also sufficient at two-instanton order. This is achieved by producing a holomorphic action of SL(2,Z) on the twistor space which preserves the holomorphic contact structure. The key step is to cancel the anomalous modular variation of the Darboux coordinates by a local holomorphic contact transformation, which is generated by a suitable indefinite theta series. For this purpose we introduce a new family of theta series of signature (2,n-2), find their modular completion, and conjecture sufficient conditions for their convergence, which may be of independent mathematical interest.

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Sergei Alexandrov, Sibasish Banerjee, Jan Manschot, Boris Pioline. 2017-02-17. Multiple D3-instantons and mock modular forms II. https://doi.org/10.1007/s00220-018-3114-z

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