
handle: 2123/22985
Recently, Brady, Falk and Watt introduced a simplicial complex which has the homotopy type of the Milnor fibre F_Q of the reflection arrangement associated to a finite Coxeter group W. This thesis is devoted to developing a combinatorial approach to computing the integral homology groups of F_Q based on this simplicial complex. Our main result is a chain complex of free abelian groups whose integral homology is isomorphic to that of F_Q. Each chain group is isomorphic to a tensor product of the integral group ring ZW with the top reduced homology group of a rank-selected subposet of the noncrossing partition (NCP) lattice of W. Associated to the NCP lattice of W we define two isomorphic graded Z-algebras A and B, which have similarities to the Orlik-Solomon algebra and characterise the homology of the NCP lattice. The algebra A is defined in terms of generators and relations, while the algebra B is defined in a combinatorial manner which has to do with the Hurwitz actions. In particular, each element of B (or A) produces an explicit cycle of the top reduced homology group of the corresponding interval or rank-selected subposet of the NCP lattice. This permits us to calculate the homology of our chain complex computationally. The actions of both W and the monodromy may also be partly described by our chain complex. In particular, we prove that the homology of the subcomplex of W-invariant chain groups is isomorphic to the homology of F_P=F_Q/W, the Milnor fibre of the discriminant of W. This recovers the result of Brady, Falk and Watt.
Milnor fibre, noncrossing partition lattice, 514, hyperplane arrangement, noncrossing algebras
Milnor fibre, noncrossing partition lattice, 514, hyperplane arrangement, noncrossing algebras
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