The cohomological decomposition conjecture for crystallographic groups with cyclic holonomy

Let GG be a finite cyclic group and LL a finitely generated ZG\mathbb{Z}G-lattice. For the split crystallographic group LGL\rtimes G, consider its integral cohomology and the cohomology of GG with coefficients in the cohomology of LL. Cohomological decomposition conjecture. For every k0k\geq 0, there should be an isomorphism

Hk(LG,Z)i+j=kHi(G,Hj(L,Z)).\mathrm{H}^k(L\rtimes G,\mathbb{Z})\cong\bigoplus_{i+j=k}\mathrm{H}^i(G,\mathrm{H}^j(L,\mathbb{Z})).

The conjecture extends the known prime-order cyclic holonomy case. It is refuted by counterexamples, including examples in dimensions at most 55 and an example with odd-order holonomy GZ9G\cong\mathbb{Z}_9 in dimension 88.

Sources & referencesView supporting material

Primary source

Nansen Petrosyan and Bartosz Putrycz, “On cohomology of crystallographic groups with cyclic holonomy of split type”, arXiv:1106.4216 (2011).

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