ScalingStacks

Proof. [04PY]

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Proof.

Over Int​(τ)\textrm{Int}(\tau) of any 22-dimensional face τ⊂Sk⁡(𝒳)\tau\subset\Sk(\mathscr{X}), ρ¯\overline{\rho} is equal to ρ𝒵\rho_{\mathscr{Z}}, hence is an affinoid torus fibration. Around any vertex vDv_{D}, ρ¯\overline{\rho} is equal to ρ𝒳i​j​k\rho_{\mathscr{X}_{ijk}} for any triple such that D≠Di,Dj,DkD\neq D_{i},D_{j},D_{k}. It follows from Section 3.3.1 that ρ¯\overline{\rho} is an affinoid torus fibration around vDv_{D}. We denote by p0+p∞p_{0}+p_{\infty} the boundary of CeC_{e}, with p0=Ce∩Di0p_{0}=C_{e}\cap D_{i_{0}} and p∞=Ce∩Di∞p_{\infty}=C_{e}\cap D_{i_{\infty}}; we write ae,0=vDe1a_{e,0}=v_{D_{e_{1}}} and ae,5=vDe2a_{e,5}=v_{D_{e_{2}}}, and denote by (⋅,⋅)(\cdot,\cdot) the open segment joining two points. Then, for j∈{0,…,4}j\in\{0,\ldots,4\}, ρ¯\overline{\rho} is equal to ρ𝒳e,j\rho_{\mathscr{X}_{e,j}} over Int​(τp0)∪Int​(τp∞)∪(ae,j,ae,j+1)\textrm{Int}(\tau_{p_{0}})\cup\textrm{Int}(\tau_{p_{\infty}})\cup(a_{e,j},a_{e,j+1}), thus is an affinoid torus fibration. We conclude that ρ¯\overline{\rho} is an affinoid torus fibration away from the points ae,ia_{e,i} for i∈{1,…,4}i\in\{1,\ldots,4\} .

For a singular point ae,ia_{e,i}, we consider a loop γ\gamma around it and contained in Int​(τp0)∪Int​(τp∞)∪(ae,i−1,ae,i)∪(ae,i,ae,i+1)\textrm{Int}(\tau_{p_{0}})\cup\textrm{Int}(\tau_{p_{\infty}})\cup(a_{e,i-1},a_{e,i})\cup(a_{e,i},a_{e,i+1}). We apply Corollary 3.2.4 to compute the monodromy along γ\gamma: the numbers be1,𝒳e,i−1b_{e_{1},\mathscr{X}_{e,i-1}} and be1,𝒳e,ib_{e_{1},\mathscr{X}_{e,i}} differ by 11, as the model 𝒳e,i\mathscr{X}_{e,i} has an additional exceptional curves in De1D_{e_{1}} with respect to 𝒳e,i−1\mathscr{X}_{e,i-1}. Therefore, we obtain

Tρ¯​(γae,i)\displaystyle T_{\overline{\rho}}(\gamma_{a_{e,i}}) =(10be1,𝒳e,i−1−be1,𝒳e,i1)\displaystyle=\left(\begin{matrix}1&0\\ b_{e_{1},\mathscr{X}_{e,i-1}}-b_{e_{1},\mathscr{X}_{e,i}}&1\end{matrix}\right)
=(103−(i−1)−(3−i)1)\displaystyle=\left(\begin{matrix}1&0\\ 3-(i-1)-(3-i)&1\end{matrix}\right)
=(1011)\displaystyle=\left(\begin{matrix}1&0\\ 1&1\end{matrix}\right)
γae,2\gamma_{a_{e,2}}ae,1a_{e,1}ae,2a_{e,2}ae,3a_{e,3}ae,4a_{e,4}v2=ve2=ae,5v_{2}=v_{e_{2}}=a_{e,5}vi∞=v4v_{i_{\infty}}=v_{4}v3=vi0v_{3}=v_{i_{0}}v1=ve1=ae,0v_{1}=v_{e_{1}}=a_{e,0}

with respect to the basis (vDi0,vDe1)(v_{D_{i_{0}}},v_{D_{e_{1}}}) and origin vDe2v_{D_{e_{2}}}. ∎

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