Tropical Lagrangian multi-sections and smoothing of locally free sheaves over degenerate Calabi-Yau surfaces

Abstract

We introduce the notion of tropical Lagrangian multi-sections over a $2$-dimensional integral affine manifold $B$ with singularities, and use them to study the reconstruction problem for higher rank locally free sheaves over Calabi-Yau surfaces. To certain tropical Lagrangian multi-sections $\mathbb{L}$ over $B$, which are explicitly constructed by prescribing local models around the ramification points, we construct locally free sheaves ${\mathcal{E}}_0(\mathbb{L},{\mathbf{k}}_s)$ over the singular projective scheme $X_0(B,\mathcal{P},s)$ associated to $B$ equipped with a polyhedral decomposition $\mathcal{P}$ and a gluing data $s$. We then find combinatorial conditions on such an $\mathbb{L}$ under which the sheaf ${\mathcal{E}}_0(\mathbb{L},{\mathbf{k}}_s)$ is simple. This produces explicit examples of smoothable pairs $(X_0(B,\mathcal{P},s),{\mathcal{E}}_0(\mathbb{L},{\mathbf{k}}_s))$ in dimension 2.

29 pages, 7 figures; v5: final version to appear in Adv. Math