On covering paths with 3 dimensional random walk

Abstract

In this paper we find an upper bound for the probability that a $3$ dimensional simple random walk covers each point in a nearest neighbor path connecting 0 and the boundary of an $L_1$ ball of radius $N$ in $\mathbb{Z} ^d$. For $d\ge 4$, it has been shown in [5] that such probability decays exponentially with respect to $N$. For $d=3$, however, the same technique does not apply, and in this paper we obtain a slightly weaker upper bound: $\forall \varepsilon >0,\exists c_\varepsilon >0,$ \[P\left ({\rm Trace}(\mathcal{P} )\subseteq{\rm Trace} \big (\{X_n\}_{n=0}^\infty \big ) \right )\le \exp \left (-c_\varepsilon N\log ^{-(1+\varepsilon )}(N)\right ).\]