ScalingStacks

Example 3.32 . [03PR]

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Example 3.32.

Example 2.16 described a family of Lagrangian MCF translators LL in ℂm{\mathbin{\mathbb{C}}}^{m} given in equation (2.10), asymptotic to the union of two Lagrangian planes Π0,Πϕ≅ℝm\Pi_{0},\Pi_{\boldsymbol{\phi}}\cong{\mathbin{\mathbb{R}}}^{m} intersecting in ℝ{\mathbin{\mathbb{R}}}. We have sketched LL in Figure 3.9 (not easy to draw in only two dimensions).

⟶\textstyle{\longrightarrow}direction oftranslationintersection of LL with zmz_{m}-axisJJ-holomorphic curve Σ\SigmaΠ~0\textstyle{\tilde{\Pi}_{0}}Π~ϕ\textstyle{\tilde{\Pi}_{\boldsymbol{\phi}}}L\textstyle{L}

Figure 3.9: Joyce–Lee–Tsui Lagrangian MCF translator from Example 2.16

We indicate the intersection of LL with the zmz_{m}-axis, the curve

L∩\displaystyle L\,\cap\, {(0,…,0,zm):zm∈ℂ}={(0,…,0,\displaystyle\bigl\{(0,\ldots,0,z_{m}):z_{m}\in{\mathbin{\mathbb{C}}}\bigr\}=\bigl\{\bigl(0,\ldots,0,
12y2−iα∑j=1m−1ψj(y)−iαarg(y+iP(y)−1/2)):y∈ℝ},\displaystyle{\textstyle\frac{1}{2}}y^{2}-\textstyle\frac{i}{\alpha}\sum_{j=1}^{m-1}\psi_{j}(y)-\textstyle\frac{i}{\alpha}\arg(y+iP(y)^{-1/2})\bigr):y\in{\mathbin{\mathbb{R}}}\bigr\},

which bounds a noncompact JJ-holomorphic curve Σ\Sigma in the zmz_{m}-axis as shown.

We will try and describe a type II singularity of Lagrangian MCF {Lt:t∈[0,T)}\{L^{t}:t\in[0,T)\} with a singularity at x∈Mx\in M modelled on these LMCF translators LL, using Principle 3.9(b). Identifying MM with TxM≅ℂmT_{x}M\cong{\mathbin{\mathbb{C}}}^{m} near x∈Mx\in M, each LtL^{t} should to ‘first order’ approximate an LMCF translator LL from Example 2.16, and as t→Tt\rightarrow T these LMCF translators should slowly shrink homothetically, as well as translate. What interests us is the ‘second order’ changes to LL which cause this shrinking.

Far to the right in Figure 3.9, the LMCF translator LL approximates two non-intersecting affine Lagrangian planes Π~0,Π~ϕ\tilde{\Pi}_{0},\tilde{\Pi}_{\boldsymbol{\phi}} in ℂm{\mathbin{\mathbb{C}}}^{m} from (2.11), just as far to the right in Figure 2.1, the ‘grim reaper’ approximates two non-intersecting parallel lines in ℂ{\mathbin{\mathbb{C}}}. I suggest that to ‘second order’ in LtL^{t}, the two planes Π~0,Π~ϕ\tilde{\Pi}_{0},\tilde{\Pi}_{\boldsymbol{\phi}} should be bent towards each other by a small angle, introducing a new immersed self-intersection point, and so that the noncompact JJ-holomorphic curve Σ\Sigma becomes a compact ‘teardrop’ as in Figure 2.3, which makes H​F∗HF^{*} obstructed. This modification L~\tilde{L} of LL is sketched in Figure 3.10.

∙\textstyle{\bullet}⟶\textstyle{\longrightarrow}direction oftranslationintersection of L~\tilde{L} with zmz_{m}-axisJJ-holomorphic curve Σ\SigmaΠ~0\textstyle{\tilde{\Pi}_{0}}Π~ϕ\textstyle{\tilde{\Pi}_{\boldsymbol{\phi}}}L~\textstyle{\tilde{L}}

Figure 3.10: Modification L~\tilde{L} of Joyce–Lee–Tsui LMCF translator

I expect that this ‘bending’ of Π~0,Π~ϕ\tilde{\Pi}_{0},\tilde{\Pi}_{\boldsymbol{\phi}} towards one another is both the ‘outside influence’ in Principle 3.9(b) which makes LL shrink and causes the finite time singularity, and also the cause of the self-intersection point, the ‘teardrop’ curve Σ\Sigma, and the obstructions to H​F∗HF^{*}.

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