Convergence of manifolds under some $L^p$-integral curvature conditions

Abstract

Let $\mathcal{C}(\mathcal{R},n,p,\Lambda,D,V_0)$ be the class of compact $n$-dimensional Riemannian manifolds with finite diameter $\leq D$, non-collapsing volume $\geq V_0$ and $L^p$-bounded $\mathcal{R}$-curvature condition $\|\mathcal{R}\|_{L^p}\leq \Lambda$ for some $p>\frac n2$. Let $(M,g_0)$ be a compact Riemannian manifold and $\mathcal{C}(M,g_0)$ the class of manifolds $(M,g)$ conformal to $(M,g_0)$. In this paper we use $\varepsilon$-regularity to show a rigidity result in the conformal class $\mathcal{C}(S^n,g_0)$ of standard sphere under $L^p$-scalar rigidity condition. Then we use harmonic coordinate to show $C^{\alpha}$-compactness of the class $\mathcal{C}(K,n,p,\Lambda,D,V_0)$ with additional positive Yamabe constant condition, where $K$ is the sectional curvature, and this result will imply a generalization of Mumford's lemma. Combining these methods together we give a geometric proof of $C^{\alpha}$-compactness of the class $\mathcal{C}(K,n,p,\Lambda,D,V_0)\cap \mathcal{C}(M,g_0)$. By using Weyl tensor and a blow down argument, we can replace the sectional curvature condition by Ricci curvature and get our main result that the class $\mathcal{C}(Ric,n,p,\Lambda,D,V_0)\cap \mathcal{C}(M,g_0)$ has $C^{\alpha}$-compactness.