Articolele autorului Alexandru Ion Suciu
Link la profilul stiintific al lui Alexandru Ion Suciu

Fundamental groups of line arrangements: Enumerative aspects

This is a survey of some recent developments in the study of complements of line arrangements in the complex plane. We investigate the fundamental groups and finite covers of those complements, focusing on homological and enumerative aspects. The unifying framework for this study is the stratification of the character variety of the fundamental group, G, by the jumping loci for cohomology with coefficients in rank 1 local systems. Counting certain

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Translated tori in the characteristic varieties of complex hyperplane arrangements

We give examples of complex hyperplane arrangements A for which the top characteristic variety, V_1(A), contains positive-dimensional irreducible components that do not pass through the origin of the algebraic torus (C^*)^{|A|}. These examples answer several questions of Libgober and Yuzvinsky. As an application, we exhibit a pair of arrangements for which the resonance varieties of the Orlik-Solomon algebra are (abstractly) isomorphic, yet whose

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Systolic freedom of loop space

Given a pair of integers m and n such that 1 < m < n, we show that every n-dimensional manifold admits metrics of arbitrarily small total volume, and possessing the following property: every m-dimensional submanifold of less than unit m-volume is necessarily torsion in homology. This result is different from the case of a pair of complementary dimensions, for which a direct geometric construction works and gives the analogous theorem in complete

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Cohomology rings and nilpotent quotients of real and complex arrangements

For an arrangement with complement X and fundamental group G, we relate the truncated cohomology ring, H^{

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Characteristic varieties of arrangements

The k-th Fitting ideal of the Alexander invariant B of an arrangement A of n complex hyperplanes defines a characteristic subvariety, V_k(A), of the complex algebraic n-torus. In the combinatorially determined case where B decomposes as a direct sum of local Alexander invariants, we obtain a complete description of V_k(A). For any arrangement A, we show that the tangent cone at the identity of this variety coincides with R^1_k(A), one of the cohomology

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Riemannian manifolds, geometric inequalities, and homotopy theory

We outline the current state of knowledge regarding geometric inequalities of systolic type, and prove new results, including systolic freedom in dimension 4. Namely, every compact, orientable, smooth 4-manifold X admits metrics of arbitrarily small volume such that every orientable, immersed surface of smaller than unit area is necessarily null-homologous in X.

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Homotopy types of complements of 2-arrangements in R^4

We study the homotopy types of complements of arrangements of n transverse planes in R^4, obtaining a complete classification for n

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Volumes, middle-dimensional systoles, and Whitehead products
Alexander invariants of complex hyperplane arrangements

Let A be an arrangement of complex hyperplanes. The fundamental group of the complement of A is determined by a braid monodromy homomorphism from a finitely generated free group to the pure braid group. Using the Gassner representation of the pure braid group, we find an explicit presentation for the Alexander invariant of A. From this presentation, we obtain combinatorial lower bounds for the ranks of the Chen groups of A. We also provide a combinatorial

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Homology of iterated semidirect products of free groups

Let G be a group which admits the structure of an iterated semidirect product of finitely generated free groups. We construct a finite, free resolution of the integers over the group ring of G. This resolution is used to define representations of groups which act compatibly on G, generalizing classical constructions of Magnus, Burau, and Gassner. Our construction also yields algorithms for computing the homology of the Milnor fiber of a fiber-type

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