Heinz mean curvature estimates in warped product spaces $M\times_{e^ψ}N$

Abstract: If a graph submanifold $(x,f(x))$ of a Riemannian warped product space $(M^m\times_{e^{\psi}}N^n,\tilde{g}=g+e^{2\psi}h)$ is immersed with parallel mean curvature $H$, then we obtain a Heinz type estimation of the mean curvature. Namely, on each compact domain $D$ of $M$, $m|H|\leq \frac{A_{\psi}(\partial D)}{V_{\psi}(D)}$ holds, where $A_{\psi}(\partial D)$ and $V_{\psi}(D)$ are the ${\psi}$-weighted area and volume, respectively. In particular, $H=0$ if $(M,g)$ has zero weighted Cheeger constant, a concept recently introduced by D.\ Impera et al.\ (\cite{[Im]}). This generalizes the known cases $n=1$ or $\psi=0$. We also conclude minimality using a closed calibration, assuming $(M,g_)$ is complete where $g_=g+e^{2\psi}f^*h$, and for some constants $\alpha\geq \delta\geq 0$, $C_1>0$ and $\beta\in [0,1)$, $|\nabla^\psi|^2_{g_}\leq \delta$, $\mathrm{Ricci}{\psi,g}\geq \alpha$, and $det_g(g_)\leq C_1 r^{2\beta}$ holds when $r\to +\infty$, where $r(x)$ is the distance function on $(M,g_*)$ from some fixed point. Both results rely on expressing the squared norm of the mean curvature as a weighted divergence of a suitable vector field.