ScalingStacks

Theorem 6.19 . [04KS]

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Theorem 6.19.

Let U⊂ℝ3U\subset\mathbb{R}^{3}, Γc\Gamma_{c}, Γd\Gamma_{d} and Γe\Gamma_{e} be as in Example 6.18 and let (b1,b2,b3)(b_{1},b_{2},b_{3}) be coordinates on UU. Define Z¯c=T∗​Γc/⟨d​b2,d​b3⟩ℤ\bar{Z}_{c}=T^{\ast}\Gamma_{c}\,/\,\langle db_{2},db_{3}\rangle_{\mathbb{Z}}, Z¯d=T∗​Γd/⟨d​b2,d​b3⟩ℤ\bar{Z}_{d}=T^{\ast}\Gamma_{d}\,/\,\langle db_{2},db_{3}\rangle_{\mathbb{Z}} and Z¯e=T∗​Γe/⟨d​b2,d​b3⟩ℤ\bar{Z}_{e}=T^{\ast}\Gamma_{e}\,/\,\langle db_{2},db_{3}\rangle_{\mathbb{Z}} with projections π¯c\bar{\pi}^{c}, π¯d\bar{\pi}^{d}, π¯e\bar{\pi}^{e} and bundles 𝔏c=ker⁡π¯∗c\mathfrak{L}_{c}=\ker\bar{\pi}^{c}_{\ast}, 𝔏d=ker⁡π¯∗d\mathfrak{L}_{d}=\ker\bar{\pi}^{d}_{\ast}, 𝔏e=ker⁡π¯∗e\mathfrak{L}_{e}=\ker\bar{\pi}^{e}_{\ast}. Suppose we are given integers m1m_{1}, m2m_{2} and sequences ℓc={ℓkc}k∈ℕ∈ℒZ¯c\ell^{c}=\{\ell_{k}^{c}\}_{k\in\mathbb{N}}\in\mathscr{L}_{\bar{Z}_{c}}, ℓd={ℓkd}k∈ℕ∈ℒZ¯d\ell^{d}=\{\ell_{k}^{d}\}_{k\in\mathbb{N}}\in\mathscr{L}_{\bar{Z}_{d}} and ℓe={ℓke}k∈ℕ∈ℒZ¯e\ell^{e}=\{\ell_{k}^{e}\}_{k\in\mathbb{N}}\in\mathscr{L}_{\bar{Z}_{e}} satisfying

∫[d​b2]ℓ1c\displaystyle\int_{[db_{2}]}\ell_{1}^{c} =\displaystyle= ∫[d​b3]ℓ1c=0,\displaystyle\int_{[db_{3}]}\ell_{1}^{c}=0,
∫[d​b2]ℓ1e\displaystyle\int_{[db_{2}]}\ell_{1}^{e} =\displaystyle= 0and∫[d​b3]ℓ1e=m2,\displaystyle 0\quad\ \ \text{and}\quad\int_{[db_{3}]}\ell_{1}^{e}=m_{2}, (60)
∫[d​b2]ℓ1d\displaystyle\int_{[db_{2}]}\ell_{1}^{d} =\displaystyle= m1and∫[d​b3]ℓ1d=0.\displaystyle m_{1}\quad\text{and}\quad\int_{[db_{3}]}\ell_{1}^{d}=0.

Then there exists a smooth symplectic manifold (X,ω)(X,\omega) and a stitched Lagrangian fibration f:X→Uf:X\rightarrow U having the same monodromy of Example 6.18 with respect to some basis γ={γ1,γ2,γ3}\gamma=\{\gamma_{1},\gamma_{2},\gamma_{3}\} of H1​(f−1​(U−(Γd∪Γe)),ℤ)H_{1}(f^{-1}(U-(\Gamma_{d}\cup\Gamma_{e})),\mathbb{Z}) and satisfying the following properties:

  • (i)

    the coordinates (b1,b2,b3)(b_{1},b_{2},b_{3}) are action coordinates of ff with moment map f∗​b1f^{\ast}b_{1};

  • (ii)

    the periods {d​b1,d​b2,d​b3}\{db_{1},db_{2},db_{3}\}, restricted to U±U^{\pm} correspond to the basis γ\gamma;

  • (iii)

    there is a Lagrangian section σ\sigma of ff, such that (Z¯c,ℓc)(\bar{Z}_{c},\ell^{c}), (Z¯d,ℓd)(\bar{Z}_{d},\,\ell^{d}) and (Z¯e,ℓe)(\bar{Z}_{e},\,\ell^{e}) are respectively the invariants of:

    (f|U−(Γd∪Γe),σ,γ),(f|U−(Γc∪Γe),σ,j+​(γ))​and​(f|U−(Γc∪Γd),σ,j+​(γ)).(f|_{U-(\Gamma_{d}\cup\Gamma_{e})},\sigma,\,\gamma),\ (f|_{U-(\Gamma_{c}\cup\Gamma_{e})},\sigma,\,j_{+}(\gamma))\ \textrm{and}\ (f|_{U-(\Gamma_{c}\cup\Gamma_{d})},\sigma,\,j_{+}(\gamma)).

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

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