Volume Doubling and Geometric Inequalities on Graphs with Bakry-Émery Curvature

Abstract

We consider irreducible reversible Markov chains whose nonzero off-diagonal transition probabilities are bounded below by $ε>0$ and whose reversible measure satisfies $m_-\le m(x)\leκm_-$. Under the Bakry--Émery curvature condition $\mathrm{CD}(K,\infty)$, with $K\in\mathbb{R}$, we establish Wang's log-Harnack inequality $$ P_t(\log f)(x)\le\log P_tf(y) +\frac{C\mathrm{dist}(x,y)^2}{\int_0^t e^{2Ks}\mathrm{d} s}, $$ for bounded positive $f$ bounded away from zero and all $x,y\in V$, where $C$ is a constant dependent only on $\varepsilon$. Building upon this inequality, we further prove volume doubling property: let $K_-:=\max\{-K,0\}$ $$ \mathrm{Vol}(B(o,2R))\le C_0\exp\!\bigl(C_1\sqrt{K_-}\,R\bigr) \mathrm{Vol}(B(o,R)),\qquad R>0, $$ where $C_0,C_1$ depend only on $ε,κ$. If $d$ is the maximum combinatorial degree of the support graph, we further prove under $\mathrm{CD}(0,\infty)$ the sharp volume growth bound $\mathrm{Vol}(B(o,R))\le m_-CR^{\lfloor d/2\rfloor}$ for all $o$ and $R\geq 1$.