## Advanced Studies in Pure Mathematics

### Cohomology rings and nilpotent quotients of real and complex arrangements

#### Abstract

For an arrangement with complement $X$ and fundamental group $G$, we relate the truncated cohomology ring, $H^{\le2} (X)$, to the second nilpotent quotient, $G/G_3$. We define invariants of $G/G_3$ by counting normal subgroups of a fixed prime index $p$, according to their abelianization. We show how to compute this distribution from the resonance varieties of the Orlik–Solomon algebra mod $p$. As an application, we establish the cohomology classification of 2-arrangements of $n \le 6$ planes in ${\mathbb{R}}^4$.

#### Article information

Dates
First available in Project Euclid: 20 August 2018

Permanent link to this document
https://projecteuclid.org/ euclid.aspm/1534788972

Digital Object Identifier
doi:10.2969/aspm/02710185

Mathematical Reviews number (MathSciNet)
MR1796900

Zentralblatt MATH identifier
0974.32020

#### Citation

Matei, Daniel; Suciu, Alexander I. Cohomology rings and nilpotent quotients of real and complex arrangements. Arrangements – Tokyo 1998, 185--215, Mathematical Society of Japan, Tokyo, Japan, 2000. doi:10.2969/aspm/02710185. https://projecteuclid.org/euclid.aspm/1534788972