ScalingStacks

Remark 3.10 . [00QG]

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Remark 3.10.

A problem when we work with the coordinates zm1,…​zmn−l,z𝔪jz^{m_{1}},\ldots z^{m_{n-l}},z^{\mathfrak{m}_{j}} is the inequality constraint to keep am0′​es​λ​(m0′)​zm0′a_{m_{0}^{\prime}}e^{s\lambda(m_{0}^{\prime})}z^{m_{0}^{\prime}} and am1′​es​λ​(m1′)​zm1′a_{m_{1}^{\prime}}e^{s\lambda(m_{1}^{\prime})}z^{m_{1}^{\prime}} as the two dominant monomials. This means such a holomorphic chart is not quite as simple as the product of D​(1)ℓD(1)^{\ell} with a long annulus in (ℂ∗)n−l(\mathbb{C}^{*})^{n-l}. In practice we will cover this region by lots of simpler charts which we call the charts of boundary type. Let PP be any point in this region, such that maxm⁡|am​es​λ​(m)​zm|\max_{m}{|a_{m}e^{s\lambda(m)}z^{m}|} is large but still comparable to 1 (to guarantee the chart overlaps nontrivially with some toric type chart). The associated chart uses the same coordinates zm1,…​zmn−l,z𝔪jz^{m_{1}},\ldots z^{m_{n-l}},z^{\mathfrak{m}_{j}} as above, but describes only a small region:

UP={|z𝔪j|≲|z𝔪j(P)|,∀j,|zmi−zmi(P)|<c|zmi(P)|,∀i},U_{P}=\{|z^{\mathfrak{m}_{j}}|\lesssim|z^{\mathfrak{m}_{j}}(P)|,\forall j,\quad|z^{m_{i}}-z^{m_{i}}(P)|<c|z^{m_{i}}(P)|,\forall i\},

where 0<c≪10<c\ll 1 is a fixed dimensional constant. These charts have an interpretation in terms of the strata 𝒜λ,σ∞\mathcal{A}_{\lambda,\sigma}^{\infty} (cf. Lemma 3.5): the point PP corresponds roughly to a point P′P^{\prime} on the face Fσ∨⊂Δλ∨F_{\sigma}^{\vee}\subset\Delta_{\lambda}^{\vee}, and allowing |z𝔪j||z^{\mathfrak{m}_{j}}| to decrease to zero corresponds to taking the Minkowski sum with the outward normal cone N​CΔ​(σ)NC_{\Delta}(\sigma), so the tropical analogue of our small chart is {P′}+N​CΔ​(Σ)\{P^{\prime}\}+NC_{\Delta}(\Sigma).

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