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Real loci in (log) Calabi–Yau manifolds via Kato–Nakayama spaces of toric degenerations

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Abstract

We study the real loci of toric degenerations of complex varieties with reducible central fibre. We show that the topology of such degenerations can be explicitly described via the Kato–Nakayama space of the central fibre as a log space. We furthermore provide generalities of real structures in log geometry and their lift to Kato–Nakayama spaces. A key point of this paper is a description of the Kato–Nakayama space of a toric degeneration and its real locus, both as bundles determined by tropical data. We provide several examples including real toric degenerations of K3-surfaces and a toric degeneration of local \({\mathbb {P}}^2\).

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Notes

  1. The discussions in Sect. 6 on real structures in log geometry and in Sect. 8 on real toric degenerations also hold in the category of schemes over \({\mathbb {R}}\).

  2. See [17, Sections A.1 and A.2] for the translation to the earlier conventions of [18, 20].

  3. The discussion in [17] is on the complement of a part \({\widetilde{\Delta }}\subset B\) of the codimension two skeleton of the barycentric subdivision. There is a retraction of to a subset of \({\widetilde{\Delta }}\). However, the discussion on monomials works on any cell not contained in and with locally toroidal at some point of \(X_\tau \).

  4. This condition is non-trivial only if \(x\in \partial B\).

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Acknowledgements

This work was a part of my PhD thesis, which would not be possible without the support of my adviser Bernd Siebert. I am also indebted to Mark Gross for many useful conversations; a major part of this paper was written during a visit to the University of Cambridge hosted by him. I am grateful to Tom Coates and Dimitri Zvonkine for their useful suggestions which improved the exposition of the paper. Finally, many thanks to anonymous referees for their very useful feedback and corrections.

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Correspondence to Hülya Argüz.

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This project has received funding from the “Research Training Group 1670 Mathematics inspired by String Theory” at Universität Hamburg funded by the Deutsche Forschungsgemeinschaft (DFG), the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 682603), and from Fondation Mathématiques Jacques Hadamard.

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Argüz, H. Real loci in (log) Calabi–Yau manifolds via Kato–Nakayama spaces of toric degenerations. European Journal of Mathematics 7, 869–930 (2021). https://doi.org/10.1007/s40879-021-00454-z

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