Abstract
To a matroidM is associated a graded commutative algebraA=A(M), the Orlik-Solomon algebra ofM. Motivated by its role in the construction of generalized hypergeometric functions, we study the cohomologyH * (A, d ω) ofA(M) with coboundary mapd ω given by multiplication by a fixed element ω ofA 1. Using a description of decomposable relations inA, we construct new examples of “resonant” values of ω, and give a precise calculation ofH 1 (A, d ω) as a function of ω. We describe the setR 1(A={ω|H 1(A(M,d ω)≠}, and use it as a tool in the classification of Orlik-Solomon algebras, with applications to the topology of complex hyperplane complements. We show thatR 1(A) is a complete invariant of the quadratic closure ofA, and show under various hypotheses that one can reconstruct the matroidM, or at least its Tutte polynomial, from the varietyR 1(A). We demonstrate with several examples thatR 1 is easily calculable, may contain nonlocal components, and that combinatorial properties ofR 1(A) are often sufficient to distinguish nonisomorphic rank three Orlik-Solomon algebras.
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Falk, M. Arrangements and cohomology. Annals of Combinatorics 1, 135–157 (1997). https://doi.org/10.1007/BF02558471
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DOI: https://doi.org/10.1007/BF02558471