Integral homology lattices of matching and circulant complexes

Abstract

Bouc's hook cycles span the rational top homology of the matching complex of $K_{2k+1}$. We prove that their integral saturation quotient has exponent exactly $2^{\lfloor k/2\rfloor}$ for every $k\geq1$, and construct divided-power cycles attaining this bound. For $k\geq2$, the homology lattice is not isomorphic to the standard integral hook lattice as an $\mathfrak S_{2k+1}$-module. For circulant complexes, we determine the integral dihedral homology modules of $\operatorname{Ind}(C_{3s}^{s-1})$, $\operatorname{Ind}(C_{3s+1}^{s-1})$ and $\operatorname{Ind}(C_{3s+2}^{s-1})$, for $s\geq3$, $s\geq2$ and $s\geq3$, respectively, and classify the least scalar lifts of all primitive equivariant quotients to the rank-one module with trivial rotation and negative reflection. Tate localization relates prime-order gluing to fixed-point homology under a free, single-degree homology hypothesis. Explicit cycle subgroups separate saturation defects from obstructions to equivariant sections. For circulant independence complexes with jumps two and three, we prove an eight-periodic ordinary homotopy classification and a fixed-space obstruction to uniform representation suspensions. For every fixed nonempty bounded positive jump set, a finite-state construction gives a rational critical-face series.