ScalingStacks

Theorem 8.3 . [01Z8]

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Theorem 8.3.

For every ϵ>0\epsilon>0 there exists δ⁡(v,ϵ)>0\delta({\rm v},\epsilon)>0 such that if M4M^{4} satisfies |RicM4|≤3​δ|{\rm Ric}_{M^{4}}|\leq 3\delta, Vol⁡(B1​(p))>v>0{\rm Vol}(B_{1}(p))>{\rm v}>0 and |𝒱4δ​(p)−𝒱1/4δ​(p)|<δ|\mathcal{V}^{\delta}_{4}(p)-\mathcal{V}^{\delta}_{1/4}(p)|<\delta, then there exists a discrete subgroup Γ⊆O⁡(4)\Gamma\subseteq{\rm O}(4) with |Γ|≤N⁡(v)|\Gamma|\leq N({\rm v}) such that the following hold:

  1. (1)

    For each x∈Aϵ,2​(p)x\in A_{\epsilon,2}(p) we have the harmonic radius lower bound rh​(x)>r0​(v)​ϵr_{h}(x)>r_{0}({\rm v})\epsilon.

  2. (2)

    There exists a subset Aϵ,2​(p)⊆U⊆Aϵ/2,2+ϵ​(p)A_{\epsilon,2}(p)\subseteq U\subseteq A_{\epsilon/2,2+\epsilon}(p) and a diffeomorphism Φ:Aϵ,2​(0)→U\Phi:A_{\epsilon,2}(0)\to U, with 0∈ℝ4/Γ0\in\mathds{R}^{4}/\Gamma, such that if gi​j=Φ∗​gg_{ij}=\Phi^{*}g is the pullback metric then

    ‖gi​j−δi​j‖C0+‖∂kgi​j‖C0<ϵ.\displaystyle||g_{ij}-\delta_{ij}||_{C^{0}}+||\partial_{k}g_{ij}||_{C^{0}}<\epsilon\,. (8.4)

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