Gradient estimates and volume doubling for locally finite weighted graphs with $CDψ(n,-K)$ condition

Abstract

We study gradient estimates and volume growth on locally finite weighted graphs satisfying the $CDψ(n,-K)$ condition with $K\geq0$. We establish a variational inequality for the heat semigroup and derive from it a family of Li-Yau type gradient estimates. Furthermore, under suitable assumptions on $ψ$, we establish a curvature dependent heat retention estimate for metric balls. Combined with a heat kernel Harnack inequality obtained from the established gradient estimate, this yields a curvature dependent exponential volume doubling estimate \begin{equation*} V(x,2r)\leq C e^{c\sqrt{K}r}V(x,r). \end{equation*} When $K=0$, the result reduces to a uniform volume doubling and further implies that the bottom of the spectrum of $-Δ$ vanishes on infinite graphs.