The cohomological decomposition conjecture for crystallographic groups with cyclic holonomy

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

Hk(L⋊G,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 G≅Z9G\cong\mathbb{Z}_9 in dimension 88.

References

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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