Spatial Brownian motion in renormalized Poisson potential: A critical case

Let $B_s$ be a three dimensional Brownian motion and $ω(dx)$ be an independent Poisson field on $\mathbb{R}^3$. It is proved that for any $t>0$, conditionally on $ω(\cdot)$, \label{*} \mathbb{E}_0 \exp\{θ\int_0^t \bar{V}(B_s) ds\} \ < \infty \ a.s. & \text{if} θ< 1/16, \medskip = \infty \ a.s. & \text{if} θ> 1/16, where $\bar{V}(x)$ is the renormalized Poisson potential $\bar{V}(x)=\int_{\mathbb{R}^3} \frac{1}{| x-y |^2} \big[ω(dy)-dy\big].$ Then the long term behavior of the quenched exponential moment \eqref{*} is determined for $θ\in (0, 1/16)$ in the form of integral tests. This paper exhibits and builds upon the interrelation between the exponential moment \eqref{*} and the celebrated Hardy's inequality $\int_{\mathbb{R}^3} \frac{f^2(x)}{| x |^2} dx \le 4 \|\nabla f\|_2^2, 2in f \in W^{1,2}(\mathbb{R}^3).$

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