Optimal Exponent for Coalescence of Finite Geodesics in Exponential Last Passage Percolation

Abstract

In this note, we study the model of directed last passage percolation on ${\mathbb{Z}}^2$, with i.i.d. exponential weight. We consider the maximum paths from vertices $\left(0,\lfloor k^{2/3}\rfloor \right)$ and $(\lfloor k^{2/3}\rfloor ,0)$ to $(n,n)$, respectively. For the coalescing point of these paths, we show that the probability for it being $>kR$ far away from the origin is in the order of $R^{-2/3}$. This is motivated by a recent work of Basu, Sarkar, and Sly, where the same estimate was obtained for semi-infinite geodesics, and the optimal exponent for the finite case was left open. Our arguments also apply to other exactly solvable models of last passage percolation.