ScalingStacks

Theorem 6.15 . [04KM]

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Theorem 6.15.

Let U⊂ℝ2U\subset\mathbb{R}^{2} be an annulus as above with coordinates (b1,b2)(b_{1},b_{2}). Let Z¯d=T∗​Γd/⟨d​b2⟩ℤ\bar{Z}_{d}=T^{\ast}\Gamma_{d}\,/\,\langle db_{2}\rangle_{\mathbb{Z}} and Z¯u=T∗​Γu/⟨d​b2⟩ℤ\bar{Z}_{u}=T^{\ast}\Gamma_{u}\,/\,\langle db_{2}\rangle_{\mathbb{Z}} with projections π¯d\bar{\pi}^{d} and π¯u\bar{\pi}^{u} and bundles 𝔏d=ker⁡π¯∗d\mathfrak{L}_{d}=\ker\bar{\pi}^{d}_{\ast} and 𝔏u=ker⁡π¯∗u\mathfrak{L}_{u}=\ker\bar{\pi}^{u}_{\ast} respectively. Given an integer mm and sequences ℓd={ℓkd}k∈ℕ∈ℒZ¯d\ell^{d}=\{\ell_{k}^{d}\}_{k\in\mathbb{N}}\in\mathscr{L}_{\bar{Z}_{d}} and ℓu={ℓku}k∈ℕ∈ℒZ¯u\ell^{u}=\{\ell_{k}^{u}\}_{k\in\mathbb{N}}\in\mathscr{L}_{\bar{Z}_{u}} such that

∫[d​b2]ℓ1u=0and∫[d​b2]ℓ1d=m,\int_{[db_{2}]}\ell_{1}^{u}=0\ \ \text{and}\ \ \int_{[db_{2}]}\ell_{1}^{d}=m,

there exists a smooth symplectic manifold (X,ω)(X,\omega) and a stitched Lagrangian fibration f:X→Uf:X\rightarrow U having monodromy (57) with respect to some basis γ={γ1,γ2}\gamma=\{\gamma_{1},\gamma_{2}\} of H1​(f−1​(U−Γd),ℤ)H_{1}(f^{-1}(U-\Gamma_{d}),\mathbb{Z}) and satisfying the following properties:

  • (i)

    the coordinates (b1,b2)(b_{1},b_{2}) are action coordinates of ff with moment map f∗​b1f^{\ast}b_{1};

  • (ii)

    the periods {d​b1,d​b2}\{db_{1},db_{2}\}, restricted to U±U^{\pm} correspond to the basis {γ1,γ2}\{\gamma_{1},\gamma_{2}\};

  • (iii)

    there is a Lagrangian section σ\sigma of ff, such that (Z¯u,ℓu)(\bar{Z}_{u},\ell^{u}) and (Z¯d,ℓd)(\bar{Z}_{d},\,\ell^{d}) are the invariants of (f−1​(U−Γd),f,U−Γd,σ,γ)(f^{-1}(U-\Gamma_{d}),\,f,\,U-\Gamma_{d},\,\sigma,\,\gamma) and (f−1​(U−Γu),f,U−Γu,σ,j+​(γ))(f^{-1}(U-\Gamma_{u}),\,f,\,U-\Gamma_{u},\,\sigma,\,j_{+}(\gamma)) respectively.

The fibration (X,f,U)(X,f,U) satisfying the above properties is unique up to fibre preserving symplectomorphism.

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