On the Invariants of the Cohomology of Complements of Coxeter Arrangements

We refine Brieskorn's study of the cohomology of the complement of the reflection arrangement of a finite Coxeter group $W$. As a result we complete the verification of a conjecture by Felder and Veselov that gives an explicit basis of the space of $W$-invariants in this cohomology ring.Comment: 12 pages, 3 figures; final versio