The automorphism-extension conjecture for models of normalizers in fusion systems

Let \calf\calf be a saturated fusion system over a pp-group SS such that Op(\calf)=1O_p(\calf)=1. Set \cale=F(\calf)\cale=F^*(\calf), a fusion subsystem over T\nsgST\nsg S, and let \call\call be a centric linking system associated to \cale\cale. Set Γ0=Aut\call(T)\Gamma_0=\operatorname{Aut}_{\call}(T), a model for N\cale(T)N_{\cale}(T). Let Γ\Gamma be a model for N\calf(T)N_{\calf}(T), and identify Γ0\Gamma_0 with a normal subgroup of Γ\Gamma. Write AutI(\call)\operatorname{Aut}^{I}(\call) for the group of isotypical automorphisms of \call\call. Automorphism-extension conjecture. There is a homomorphism τ:ΓAutI(\call)\tau:\Gamma\to\operatorname{Aut}^{I}(\call) making both triangles in the diagram commute, namely its restriction to Γ0\Gamma_0 is conjugation and the induced automorphism of Γ0\Gamma_0 agrees with conjugation by the corresponding element of Γ\Gamma:

Γ0conjAutI(\call)inclααTΓconjAut(Γ0)\begin{CD} \Gamma_0 @>{\operatorname{conj}}>> \operatorname{Aut}^{I}(\call)\\ @V{\operatorname{incl}}VV @VV{\alpha\mapsto\alpha_T}V\\ \Gamma @>{\operatorname{conj}}>> \operatorname{Aut}(\Gamma_0) \end{CD}

This is intended to provide the compatibility needed to construct extensions of fusion systems from normalizer models; the source gives no resolution.

Sources & referencesView supporting material

Primary source

Bob Oliver, “Reductions to simple fusion systems”, arXiv:1601.07978 (2016).

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