ScalingStacks

Theorem 2.5 . [03DD]

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Theorem 2.5.

The fundamental group π1​(starΣ⁡(σ^,τ^)\D)\pi_{1}(\operatorname{star}_{\Sigma}(\hat{\sigma},\hat{\tau})\backslash D) is a free group with k⋅lk\cdot l generators. In a suitable basis the monodromy

T:π1​(starΣ⁡(σ^,τ^)\D)→SL⁡(d−1,ℤ)T\colon\pi_{1}(\operatorname{star}_{\Sigma}(\hat{\sigma},\hat{\tau})\backslash D)\rightarrow\operatorname{SL}(d-1,\mathbb{Z})

can be represented (faithfully on the abelianization of π1\pi_{1}) by an index vol⁡(σ)⋅vol⁡(τ)\operatorname{vol}(\sigma)\cdot\operatorname{vol}(\tau) subgroup of the (abelian) group of matrices in the form

(10…∗…∗01…⋮⋱⋮00⋱∗…∗⋮⋮⋱⋱⋮⋮00…01000…001)\left(\begin{array}[]{cccccc}1&0&\ldots&*&\ldots&*\\ 0&1&\ldots&\vdots&\ddots&\vdots\\ 0&0&\ddots&*&\ldots&*\\ \vdots&\vdots&\ddots&\ddots&\vdots&\vdots\\ 0&0&\ldots&0&1&0\\ 0&0&\ldots&0&0&1\\ \end{array}\right)

(the identity matrix plus an l×kl\times k block in the right upper corner).

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