ScalingStacks

7.10 [037P]

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7.10

In an algebraic setting, our goal is to compare the tropical multiplicities introduced in 4.7 with the ones from Definition 7.5. Let us consider an algebraic variety XX over KK of dimension nn and an algebraic moment map φ:X→T=𝔾mr\varphi:X\rightarrow T={\mathbb{G}}_{m}^{r} over KK. We assume that the map is generically finite. Note that φtrop​(X)=Trop⁡(φ⁡(X)¯){\varphi_{\rm trop}}(X)={\rm Trop}(\overline{\varphi(X)}). We conclude that φtrop​(X){\varphi_{\rm trop}}(X) is the support of an integral Γ\Gamma-affine polyhedral complex of dimension nn endowed with the tropical multiplicities of Trop⁡(φ⁡(X)¯){\rm Trop}(\overline{\varphi(X)}). Note that this tropical multiplicities are compatible with refinement and hence they define an integer valued function malgm_{\rm alg} on the regular points of φtrop​(X){\varphi_{\rm trop}}(X). This means that the function is defined and constant in the relative interior of every nn-dimensional polyhedron σ\sigma contained in φtrop​(X){\varphi_{\rm trop}}(X) and if σ\sigma is from the above integral Γ\Gamma-affine polyhedral complex, then malg​(ω)m_{\rm alg}(\omega) is equal to the tropical multiplicity of σ\sigma in Trop⁡(φ⁡(X)¯){\rm Trop}(\overline{\varphi(X)}) for every ω∈relint⁡(σ)\omega\in{\rm relint}(\sigma).

The analytification Xan{X^{\rm an}} is not compact (unless d=0d=0), but as ∂X=∅\partial X=\emptyset, we can define tropical multiplicities in the same analytic manner as in Definition 7.5. Again, this is compatible with refinement and hence leads to a tropical multiplicity function manm_{\rm an} on the regular points of φtrop​(X){\varphi_{\rm trop}}(X).

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