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How to find an initial special Lagrangian [04DE]

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How to find an initial special Lagrangian

The question about finding the initial special Lagrangian is specific to the continuity method, and does not appear in the LMCF approach. A natural suggestion is to look for special Lagrangians near certain degenerate limits, and our relaxation of the complex Monge-Ampère equation ought to give much more flexibility. For instance, conifold degenerations are known to give rise to special Lagrangian spheres appearing as vanishing cycles [37].5252 52 While Hein and Sun’s result is highly nontrivial, the entire difficulty goes into understanding the Calabi-Yau metric near the conifold point. If we are given the license to prescribe arbitrary Kähler metrics, the problem of finding special Lagrangian vanishing spheres near the conifold point becomes easy. Another general source is to work near a suitable large complex structure limit, so that the Kähler metric can be made almost toric outside a small region, such that the torus fibres are much smaller compared to the characteristic length scale of the base. We can then attempt to find special Lagrangians via adiabatic limits, in close analogy with the standard procedure to find holomorphic curves via tropical degenerations [55]. 5353 53 The large complex structure limit is supposed to correspond to the large volume limit in the mirror, which is related to the μ\mu-stability, thus offering the hope of a mirror calculation of counting invariants. The most accessible special Lagrangians in this approach, should be obtainable by small perturbations of the torus fibres. 5454 54 The difficulty in [54] to construct SYZ special Lagrangian fibrations again comes from the Calabi-Yau metrics. If one can freely prescribe Kähler metrics, then finding a special Lagrangian torus is not difficult. The next candidate suggested by the Leray filtration of the torus fibration is already much harder.

Question 8.

Construct special Lagrangians whose toric projection to the base are small thickenings of certain 1-dimensional graphs.

One expects that locally along an edge these Lagrangians are perturbations of Tn−1×ℝT^{n-1}\times\mathbb{R}, with Tn−1T^{n-1} contained in the torus fibre direction, so that we obtain (n−1)(n-1) locally defined closed 1-forms ∫S1ω\int_{S^{1}}\omega on the base corresponding to the cycles S1⊂Tn−1S^{1}\subset T^{n-1}, and the edge is to leading approximation given by requiring these 1-forms to vanish. The local model for the junction where three edges meet, 5555 55 This is conceptually related to Matessi’s ‘Lagrangian pair of pants’ [59]. may have the following topological description. In the n=2n=2 case, we have a ‘pair of pants’ inside T2×ℝ2T^{2}\times\mathbb{R}^{2} with three asymptotic ends S1×ℝS^{1}\times\mathbb{R}; topologically this is the same as algebraic surface {z1+z2=1}⊂ℂ∗×ℂ∗\{z_{1}+z_{2}=1\}\subset\mathbb{C}^{*}\times\mathbb{C}^{*}. In higher dimensions, we take a product of the pair of pants with Tn−2T^{n-2}.

In the next order of perturbation, we expect the deformation of the Lagrangian in the base direction to be at least comparable to the length scale of the fibre, and presumably is fixed by the ‘special condition’ Im​Ω|L=0\text{Im}\Omega|_{L}=0.

Remark 4.2.

From the viewpoint of the Thomas-Yau-Joyce picture, there is an additional problem to assign unobstructed brane structures to the initial special Lagrangian.

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