Motivated by the Milnor fiber of a central arrangement, we study the cohomology of a family of cyclic covers of the complement of an arbitrary arrangement. We give an explicit proof of the polynomial periodicity of the Betti numbers of the members of this family of cyclic covers.
We compute the cohomology of the complement of toric arrangements associated to root systems as representations of the corresponding Weyl groups. Specifically, we develop an algorithm for computing the cohomology of the complement of toric arrangements associated to general root systems and we carry out this computation for the exceptional root systems $G_2$, $F_4$, $E_6$ and $E_7$. We also compute the total cohomology of the complement of the toric arrangement associated to $A_n$ as a representation of the Weyl group and give a formula for its Poincaré polynomial.
Let $\mathcal A$ be a hyperplane arrangement in $\mathbb C^n$. We show that the number of decomposition factors as a perverse sheaf of the direct image $Rj_*\mathbb C_U $ of the constant sheaf on the complement $U$ to the arrangement is given by the Poincaré polynomial of the arrangement. Furthermore we describe the composition factors of $Rj_*\mathbb C_U $ as certain local cohomology sheaves and give their multiplicity.
Homology of Local Systems on Real Line Arrangement Complements
Qiuzhen College, Tsinghua University(清华大学丘成桐大学);Center for Mathematics and Interdisciplinary Sciences, Fudan University(复旦大学数学与交叉科学研究院);Shanghai Institute for Mathematics and Interdisciplinary Sciences (SIMIS)(上海数学与交叉科学研究院)
We prove that the mod $2$ Betti numbers of double coverings of a complex hyperplane arrangement complement are combinatorially determined. The proof is based on a relation between the mod $2$ Aomoto complex and the transfer long exact sequence. Applying the above result to the icosidodecahedral arrangement ($16$ planes in the three dimensional space related to the icosidodecahedron), we conclude that the first homology of the Milnor fiber has non-trivial $2$-torsion.
On the homotopy type of the complement of an arrangement that is a 2-generic section of the parallel connection of an arrangement and a pencil of lines
Non-vanishing of homotopy groups of Manin--Schechtman arrangements
Institute for Chemical Reaction Design and Discovery, Hokkaido University(化学反应用设计发现研究所,北海道大学);Department of Applied Mathematics, Fukuoka University(福冈大学应用数学系)
We study geometric structures on the complement of a toric mirror arrangement associated with a root system. Inspired by those special hypergeometric functions found by Heckman-Opdam, as well as the work of Couwenberg-Heckman-Looijenga on geometric structures on projective arrangement complements, we consider a family of connections on a total space, namely, a $\mathbb{C}^{\times}$-bundle on the complement of a toric mirror arrangement (=finite union of hypertori, determined by a root system). We prove that these connections are torsion free and flat, and hence define a family of affine struct…
Let $\mathscr{A}$ be a real projective line arrangement and $M(\mathscr{A})$ its complement in $\mathbb{CP}^2$. We obtain an explicit expression in terms of Randell's generators of the meridians around the exceptional divisors in the blow-up $\bar{X}$ of $\mathbb{CP}^2$ in the singular points of $\mathscr{A}$. We use this to investigate the partial compactifications of $M(\mathscr{A})$ contained in $\bar{X}$ and give a counterexample to a statement suggested by A. Dimca and P. Eyssidieux to the effect that the fundamental group of such an algebraic variety is finite whenever its abelianization…
We compute the total cohomology of the complement of the toric arrangement associated to the root system $A_n$ as a representation of the corresponding Weyl group via fixed point theory of a "twisted" action of the group. We also provide several proofs of an explicit formula for the Poincaré polynomial of the complement of the toric arrangement associated with $A_n$.
Let $Ω$ be the complement of a connected, essential hyperplane arrangement. We prove that every dominant endomorphism of $Ω$ extends to an endomorphism of the tropical compactification $X$ of $Ω$ associated to the Bergman fan structure on the tropicalization of $Ω$. This generalizes a previous result by Rémy, Thuillier and the second author which states that every automorphism of Drinfeld's half-space over a finite field $\mathbb{F}_q$ extends to an automorphism of the successive blow-up of projective space at all $\mathbb{F}_q$-rational linear subspaces. This successive blow-up is in fact the…
Some projective wonderful models for the complement of a toric arrangement in a n-dimensional algebraic torus T were constructed in [3]. In this paper we describe their integer cohomology rings by generators and relations.