ScalingStacks

Theorem 7.4 (Naber-Zhang, [ NZ16 ] ) . [03J6]

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Theorem 7.4 (Naber-Zhang, [NZ16]).

Let (Mn,g,p)(M^{n},g,p) satisfy Ricg≡λ​g\Ric_{g}\equiv\lambda g and |λ|≤n−1|\lambda|\leq n-1. Given a manifold (Zk,zk)(Z^{k},z^{k}) with k=dim(Zk)<nk=\dim(Z^{k})<n, there are uniform constants δ0>0\delta_{0}>0, w0>0w_{0}>0 and C0>0C_{0}>0 which depend only on nn and the geometry of B1​(zk)B_{1}(z^{k}) such that the following property holds: if

(7.39) dG​H​(B2​(p),B2​(zk))<δ0,d_{GH}(B_{2}(p),B_{2}(z^{k}))<\delta_{0},

then the group Γδ0(p)≡Image[π1(Bδ0(p))→π1(B2(p))]\Gamma_{\delta_{0}}(p)\equiv\Image[\pi_{1}(B_{\delta_{0}}(p))\to\pi_{1}(B_{2}(p))] has a nilpotent subgroup 𝒩\mathcal{N} of index bounded by w0w_{0} such that rank⁡(𝒩)≤n−k\rank(\mathcal{N})\leq n-k.

Furthermore, if rank⁡(𝒩)=n−k\rank(\mathcal{N})=n-k, then supB1​(p)|Rm|≤C0\sup\limits_{B_{1}(p)}|\Rm|\leq C_{0}. Conversely, if supB3​(p)|Rm|≤C0\sup\limits_{B_{3}(p)}|\Rm|\leq C_{0}, then rank⁡(𝒩)=n−k\rank(\mathcal{N})=n-k.

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