Sharpness for fusion systems

Let F\mathcal{F} be a saturated fusion system on a finite pp-group SS. Write O(Fc)\mathcal{O}(\mathcal{F}^c) for the centric orbit category, whose objects are the F\mathcal{F}-centric subgroups of SS, and consider, for each j0j\geq 0, the cohomology functor with trivial coefficients

Hj(;Fp) ⁣:O(Fc)Fp-mod.H^j(-;\mathbb{F}_p)\colon\mathcal{O}(\mathcal{F}^c)\rightarrow \mathbb{F}_p\text{-}\mathsf{mod}.

Sharpness for fusion systems. For all i1i\geq 1 and j0j\geq 0, the higher limits vanish:

limO(Fc)iHj(;Fp)=0.\varprojlim^i_{\mathcal{O}(\mathcal{F}^c)} H^j(-;\mathbb{F}_p)=0.

This asserts that the subgroup decomposition of the classifying space of a saturated fusion system is sharp, generalizing the corresponding result for finite groups proved by Dwyer. The conjecture remains open in the general fusion-system setting.

Sources & referencesView supporting material

Primary source

Antonio Díaz and Sejong Park, “Mackey functors and sharpness for fusion systems”, arXiv:1211.3557 (2014).

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