Sharp diameter estimates for compact manifold with boundary

Let $(N,g)$ be an $n$-dimensional complete Riemannian manifold with nonempty boundary $\text{pt}N$. Assume that the Ricci curvature of $N$ has a negative lower bound $Ric\ge -(n-1)c^2$ for some $c>0$, and the mean curvature of the boundary $\text{pt}N$ satisfies $H\ge (n-1)c_0>(n-1)c$ for some $c_0>c>0$. Then a known result (see \cite{LN}) says that $\sup_{x\in N}d(x,\pt N)\leq \frac 1c\coth^{-1}\frac{c_0}c$\mathrm{.}Inthispaper,weprovethatiftheboundary$\pt N$iscompact,thentheequalityholdsifandonlyif$N$ is isometric to the geodesic ball of radius $\frac{1}{c}{\coth }^{-1}\frac{c_0}{c}$ in an $n$-dimensional hyperbolic space ${\mathbb{H}}^n(-c^2)$ of constant sectional curvature $-c^2$. Moreover, we also prove an analogous result for manifold with nonempty boundary and with $m$-Bakry-'{E}mery Ricci curvature bounded below by a negative constant.