Gumbel laws in the symmetric exclusion process

We consider the symmetric exclusion particle system on $\mathbb{Z}$ starting from an infinite particle step configuration in which there are no particles to the right of a maximal one. We show that the scaled position $X_t\mathrm{/}(\sigma b_t)-a_t$ of the right-most particle at time $t$ converges to a Gumbel limit law, where $b_t=\sqrt{t\mathrm{/}\log t}$, $a_t=\log (t\mathrm{/}(\sqrt{2\pi }\log t))$, and $\sigma$ is the standard deviation of the random walk jump probabilities. This work solves a problem left open in Arratia (1983). Moreover, to investigate the influence of the mass of particles behind the leading one, we consider initial profiles consisting of a block of $L$ particles, where $L\to \mathrm{\infty }$ as $t\to \mathrm{\infty }$. Gumbel limit laws, under appropriate scaling, are obtained for $X_t$ when $L$ diverges in $t$. In particular, there is a transition when $L$ is of order $b_t$, above which the displacement of $X_t$ is similar to that under a infinite particle step profile, and below which it is of order $\sqrt{t\log L}$. Proofs are based on recently developed negative dependence properties of the symmetric exclusion system. Remarks are also made on the behavior of the right-most particle starting from a step profile in asymmetric nearest-neighbor exclusion, which complement known results.