Universal cover of Salvetti’s complex and topology of simplicial arrangements of hyperplanes

Author:

Paris Luis

Abstract

Let V V be a real vector space. An arrangement of hyperplanes in V V is a finite set A \mathcal {A} of hyperplanes through the origin. A chamber of A \mathcal {A} is a connected component of V ( H A H ) V - ({ \cup _{H \in \mathcal {A}}}H) . The arrangement A \mathcal {A} is called simplicial if H A H = { 0 } { \cap _{H \in \mathcal {A}}}H = \{ 0\} and every chamber of A \mathcal {A} is a simplicial cone. For an arrangement A \mathcal {A} of hyperplanes in V V , we set \[ M ( A ) = V C ( H A H C ) , M(\mathcal {A}) = {V_\mathbb {C}} - \left ({\bigcup \limits _{H \in \mathcal {A}} {{H_\mathbb {C}}} } \right ), \] where V C = C V {V_\mathbb {C}} = \mathbb {C} \otimes V is the complexification of V V , and, for H A H \in \mathcal {A} , H C {H_\mathbb {C}} is the complex hyperplane of V C {V_\mathbb {C}} spanned by H H . Let A \mathcal {A} be an arrangement of hyperplanes of V V . Salvetti constructed a simplicial complex Sal ( A ) \operatorname {Sal}(\mathcal {A}) and proved that Sal ( A ) \operatorname {Sal}(\mathcal {A}) has the same homotopy type as M ( A ) M(\mathcal {A}) . In this paper we give a new short proof of this fact. Afterwards, we define a new simplicial complex Sal ^ ( A ) \hat {\operatorname {Sal}}(\mathcal {A}) and prove that there is a natural map p : Sal ^ ( A ) Sal ( A ) p:\hat {\operatorname {Sal}}(\mathcal {A}) \to \operatorname {Sal}(\mathcal {A}) which is the universal cover of Sal ( A ) \operatorname {Sal}(\mathcal {A}) . At the end, we use Sal ^ ( A ) \hat {\operatorname {Sal}}(\mathcal {A}) to give a new proof of Deligne’s result: "if A \mathcal {A} is a simplicial arrangement of hyperplanes, then M ( A ) M(\mathcal {A}) is a K ( π , 1 ) K(\pi ,1) space." Namely, we prove that Sal ^ ( A ) \hat {\operatorname {Sal}}(\mathcal {A}) is contractible if A \mathcal {A} is a simplicial arrangement.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference16 articles.

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1. K(π,1) conjecture for Artin groups;Annales de la Faculté des sciences de Toulouse : Mathématiques;2014-04-06

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