ScalingStacks

Remark 3.1.5 . [04PF]

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Remark 3.1.5.

Consider an irreducible component DiD_{i} of 𝒳k\mathscr{X}_{k} and write Ξ”Di=βˆ‘jβ‰ iDj∩Di\Delta_{D_{i}}=\sum_{j\neq i}D_{j}\cap D_{i}. By adjunction, the pair (Di,Ξ”Di)(D_{i},\Delta_{D_{i}}) is log Calabi–Yau, i.e. DiD_{i} is a smooth projective variety over kk and Ξ”Di\Delta_{D_{i}} is a divisor such that KDi+Ξ”DiK_{D_{i}}+\Delta_{D_{i}} is trivial. By [EM21, Theorem 6.14] there exists a Lagrangian torus fibration

Ο•:𝒰→BβŠ†Star⁑(vDi)βˆ–W\phi:\mathcal{U}\rightarrow B\subseteq\Star(v_{D_{i}})\setminus W

where 𝒰\mathcal{U} is a symplectic tubular neighborhood of the 11-dimensional strata of Ξ”Di\Delta_{D_{i}}, BB is a retract of Star⁑(vDi)βˆ–W\Star(v_{D_{i}})\setminus W, and WW is the union of cells of codimension β©Ύ2\geqslant 2 in Sk⁑(𝒳)\Sk(\mathscr{X}). The fibration Ο•\phi is constructed gluing toric moment maps defined in the neighborhood of each stratum curve of Ξ”Di\Delta_{D_{i}}. Evans and Mauri compare the monodromy TΟ•T_{\phi} induced by Ο•\phi on BB to the monodromy Tρ𝒳T_{\rho_{\mathscr{X}}} induced by the affinoid torus fibration

ρ𝒳:Οπ’³βˆ’1​(Star⁑(vDi)βˆ–W)β†’Star⁑(vDi)βˆ–W{\rho_{\mathscr{X}}}:\rho_{\mathscr{X}}^{-1}(\Star(v_{D_{i}})\setminus W)\rightarrow\Star(v_{D_{i}})\setminus W

and conclude that they are dual. This means that given a loop Ξ³βˆˆΟ€1​(B)≃π1​(Star⁑(vDi)βˆ–W)\gamma\in\pi_{1}(B)\simeq\pi_{1}(\Star(v_{D_{i}})\setminus W), we have Tρ𝒳​(Ξ³)=(Tϕ​(Ξ³)βˆ’1)TT_{\rho_{\mathscr{X}}}(\gamma)=(T_{\phi}(\gamma)^{-1})^{T}. Thus the affine structure constructed in [NXY19] has a symplectic topological analog. The duality is due to the fact that the image of the moment maps is MℝM_{\mathbb{R}}, while the image of the tropicalization map val\val is in NℝN_{\mathbb{R}}.

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