ScalingStacks

Proof. [05E3]

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Proof.

By Lemma 4.5, there is a unique C1C^{1}-map

σk:BhE(0,3​r2)⟶C1,α(dΩ0(Tn)⊕d∗hΩ2(Tn)),byy↦σk(y),\sigma_{k}:B_{h_{E}}(0,\frac{3r}{2})\longrightarrow C^{1,\alpha}(d\Omega^{0}(T^{n})\oplus d^{*_{h}}\Omega^{2}(T^{n})),\ \ {\rm by}\ \ y\mapsto\sigma_{k}(y),

which satisfies

𝔉k​(y,σk​(y))=0,‖σk​(y)‖C1,α​(L,h)≤δ≪1,\mathfrak{F}_{k}(y,\sigma_{k}(y))=0,\ \ \ \|\sigma_{k}(y)\|_{C^{1,\alpha}(L,h)}\leq\delta\ll 1,
and‖D​σk​(y)‖≤2​n​δ​C¯​C​‖(d​αk,d​βk)‖C1,α​(Y2​r,g).{\rm and}\ \ \ \|D\sigma_{k}(y)\|\leq 2n\delta\overline{C}C\|(d\alpha_{k},d\beta_{k})\|_{C^{1,\alpha}(Y_{2r},g)}.

This implies

|∂σk,j​(y)∂yi|≤2​n​δ​C¯​C​‖(d​αk,d​βk)‖C1,α​(Y2​r,g)≪1,|\frac{\partial\sigma_{k,j}(y)}{\partial y_{i}}|\leq 2n\delta\overline{C}C\|(d\alpha_{k},d\beta_{k})\|_{C^{1,\alpha}(Y_{2r},g)}\ll 1,

for k≫k1>1k\gg k_{1}>1.

Define a map Ψk:Y32​r⟶Y2​r\Psi_{k}:Y_{\frac{3}{2}r}\longrightarrow Y_{2r} by

Ψk:(x,y)↦(x,y1+σk,1​(y),⋯,yn+σk,n​(y))=(x,y+σk​(y)).\Psi_{k}:(x,y)\mapsto(x,y_{1}+\sigma_{k,1}(y),\cdots,y_{n}+\sigma_{k,n}(y))=(x,y+\sigma_{k}(y)).

Note that the frame field d​x1,⋯,d​xndx_{1},\cdots,dx_{n} induces local coordinates x1,⋯,xnx_{1},\cdots,x_{n} around any point on LL, and the differential can be expressed as

d​Ψk:(x˙,y˙)↦(x˙j+∑∂σk,j​(y)∂xi​x˙i,y˙j+∑∂σk,j​(y)∂yi​y˙i)d\Psi_{k}:(\dot{x},\dot{y})\mapsto(\dot{x}_{j}+\sum\frac{\partial\sigma_{k,j}(y)}{\partial x_{i}}\dot{x}_{i},\dot{y}_{j}+\sum\frac{\partial\sigma_{k,j}(y)}{\partial y_{i}}\dot{y}_{i})

under such local coordinates. Thus d​Ψkd\Psi_{k} is an isomorphism when k≫1k\gg 1, which implies that Ψk\Psi_{k} is an immersion. Furthermore, for y1≠y2∈ℝny_{1}\neq y_{2}\in\mathbb{R}^{n},

Ψk​(x,y2)−Ψk​(x,y1)\displaystyle\Psi_{k}(x,y_{2})-\Psi_{k}(x,y_{1}) =\displaystyle= (x,⋯,∫01(1+∂σk,j​((1−t)​y2+t​y1)∂yj​𝑑t)​(y2,j−y1,j),⋯)\displaystyle(x,\cdots,\int_{0}^{1}(1+\frac{\partial\sigma_{k,j}((1-t)y_{2}+ty_{1})}{\partial y_{j}}dt)(y_{2,j}-y_{1,j}),\cdots)
≠\displaystyle\neq 0.\displaystyle 0.

Hence Ψk\Psi_{k} is an embedding.

Note that the Γ\Gamma-action on Y2​r=Tn×BhE​(0,2​r)Y_{2r}=T^{n}\times B_{h_{E}}(0,2r) preserves ωk,gk,Ωk,ω,g,Ω\omega_{k},g_{k},\Omega_{k},\omega,g,\Omega, and is a product action on Tn×BhE​(0,2​r)T^{n}\times B_{h_{E}}(0,2r), i.e. there are Γ\Gamma-actions on TnT^{n} and BhE​(0,2​r)B_{h_{E}}(0,2r) such that γ⋅(x,y)=(γ⋅x,γ⋅y)\gamma\cdot(x,y)=(\gamma\cdot x,\gamma\cdot y) for any γ∈Γ\gamma\in\Gamma, x∈Tnx\in T^{n}, and y∈BhE​(0,2​r)y\in B_{h_{E}}(0,2r). Under the identification map (1),

(γ⋅x,γ⋅y)=(γ⋅x,ι⁡(γ∗​∑jyj​∂∂yj)​ω)\displaystyle(\gamma\cdot x,\gamma\cdot y)=(\gamma\cdot x,\iota(\gamma_{*}\sum_{j}y_{j}\frac{\partial}{\partial y_{j}})\omega) =\displaystyle= (γ⋅x,γ∗ω(∑jyj∂∂yj,γ∗−1⋅))\displaystyle(\gamma\cdot x,\gamma^{*}\omega(\sum_{j}y_{j}\frac{\partial}{\partial y_{j}},\gamma^{-1}_{*}\cdot))
=\displaystyle= (γ⋅x,γ−1,∗​∑jyj​d​xj).\displaystyle(\gamma\cdot x,\gamma^{-1,*}\sum_{j}y_{j}dx_{j}).

Thus

γ⋅L⁡(y,σk​(y))\displaystyle\gamma\cdot L(y,\sigma_{k}(y)) =\displaystyle= {(γ⋅x,γ⋅(y1+σk,1​(y)​(x),⋯,yn+σk,n​(y)​(x)))|x∈Tn}\displaystyle\{(\gamma\cdot x,\gamma\cdot(y_{1}+\sigma_{k,1}(y)(x),\cdots,y_{n}+\sigma_{k,n}(y)(x)))|x\in T^{n}\}
=\displaystyle= {(γ⋅x,γ−1,∗∑j(yj+σk,j(y)(x))dxj|x∈Tn}\displaystyle\{(\gamma\cdot x,\gamma^{-1,*}\sum_{j}(y_{j}+\sigma_{k,j}(y)(x))dx_{j}|x\in T^{n}\}
=\displaystyle= L⁡(γ⋅y,γ−1,∗​σk​(y)),\displaystyle L(\gamma\cdot y,\gamma^{-1,*}\sigma_{k}(y)),

for any γ∈Γ\gamma\in\Gamma and y∈BhE​(0,2​r)y\in B_{h_{E}}(0,2r). Since the Γ\Gamma-action preserves ωk\omega_{k} and Ωk\Omega_{k}, L⁡(γ⋅y,γ−1,∗​σk​(y))L(\gamma\cdot y,\gamma^{-1,*}\sigma_{k}(y)) are special lagrangian submanifolds. By the uniqueness of σk​(y)\sigma_{k}(y), γ−1,∗σk(y)=σk(γ⋅y)∈C1,α(dΩ0(Tn)⊕d∗hΩ2(Tn))\gamma^{-1,*}\sigma_{k}(y)=\sigma_{k}(\gamma\cdot y)\in C^{1,\alpha}(d\Omega^{0}(T^{n})\oplus d^{*_{h}}\Omega^{2}(T^{n})). Hence

Ψk​(γ⋅x,γ⋅y)\displaystyle\Psi_{k}(\gamma\cdot x,\gamma\cdot y) =\displaystyle= (γ⋅x,γ⋅y+σk​(γ⋅y))\displaystyle(\gamma\cdot x,\gamma\cdot y+\sigma_{k}(\gamma\cdot y))
=\displaystyle= (γ⋅x,γ−1,∗​∑j(yj+σk,j​(y))​d​xj)\displaystyle(\gamma\cdot x,\gamma^{-1,*}\sum_{j}(y_{j}+\sigma_{k,j}(y))dx_{j})
=\displaystyle= (γ⋅x,γ⋅(y1+σk,1​(y),⋯,yn+σk,n​(y)))\displaystyle(\gamma\cdot x,\gamma\cdot(y_{1}+\sigma_{k,1}(y),\cdots,y_{n}+\sigma_{k,n}(y)))
=\displaystyle= γ⋅Ψk​(x,y),\displaystyle\gamma\cdot\Psi_{k}(x,y),

i.e. Ψk\Psi_{k} is a Γ\Gamma-equivariant map.

We denote 𝒫:Y2​r⟶BhE​(0,2​r)\mathcal{P}:Y_{2r}\longrightarrow B_{h_{E}}(0,2r) the natural projection, Bk=BhE​(0,32​r)B_{k}=B_{h_{E}}(0,\frac{3}{2}r) and Wk=Ψk​(Y32​r)W_{k}=\Psi_{k}(Y_{\frac{3}{2}r}). Since the Γ\Gamma-action on BhE​(0,2​r)B_{h_{E}}(0,2r) preserves the metric hEh_{E} and 00, Bk=BhE​(0,32​r)B_{k}=B_{h_{E}}(0,\frac{3}{2}r) is invariant. By δ≪1≪r\delta\ll 1\ll r, Wk⊃YrW_{k}\supset Y_{r}. Then fk=𝒫∘Ψk−1:Wk⟶Bkf_{k}=\mathcal{P}\circ\Psi_{k}^{-1}:W_{k}\longrightarrow B_{k} is a Γ\Gamma-equivariant special lagrangian fibration of (Wk,ωk,Ωk)(W_{k},\omega_{k},\Omega_{k}) of phase θk\theta_{k}. We obtain the conclusion. ∎

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