Convergence in Wasserstein Distance for Empirical Measures of Dirichlet Diffusion Processes on Manifolds

Let $M$ be a $d$-dimensional connected compact Riemannian manifold with boundary $\mathrm{\partial }M$, let $V\in C^2(M)$ such that $\mu({\rm d} x):={\rm e}^{V(x)}{\rm d} x$isaprobabilitymeasure,andlet$X_t$ be the diffusion process generated by $L:=\mathrm{\Delta }+\mathrm{\nabla }V$ with $\tau:=\inf{t\ge 0: X_t\in\partial M}$\mathrm{.}Considertheempiricalmeasure$\mu_t:=\frac 1 t \int_0^t \delta_{X_s}{\rm d} s$underthecondition$t<\tau$ for the diffusion process. If $d\le 3$, then for any initial distribution not fully supported on $\partial M$, \begin{align*} &c\sum_{m=1}^\infty \frac{2}{(\lambda_m-\lambda_0)^2} \le \liminf_{t\to \infty} \inf_{T\ge t} \Big{t {\mathbb E}\big[\mathbb W_2(\mu_t, \mu_0)^2\big|T<\tau\big]\Big} \ &\le \limsup_{t\to \infty} \sup_{T\ge t} \Big{ t \mathbb E\big[\mathbb W_2(\mu_t, \mu_0)^2\big|T<\tau\big] \Big}\le \sum_{m=1}^\infty \frac{2}{(\lambda_m-\lambda_0)^2}\end{align*} holds for some constant $c\in (0,1]$ with $c=1$ when $\mathrm{\partial }M$ is convex, where $\mu_0:= \phi_0^2\mu$forthefirstDiricheteigenfunction$\phi_0$of$L$,${\lambda_m}{m\ge 0}$aretheDirichleteigenvaluesof$-L$ listed in the increasing order counting multiplicities, and the upper bound is finite if and only if $d\le 3$. When $d=4$, $\sup{T\ge t} \mathbb E\big[\mathbb W_2(\mu_t, \mu_0)^2\big|T<\tau\big] $decaysintheorder$t^{-1}\log t$,whilefor$d\ge 5$itbehaveslike$t^{-\frac 2 {d-2}}$,as$t\to\infty$.