Probing multi-particle unitarity with the Landau equations

We consider the $2\to 2$ scattering amplitude of identical massive particles. identify Landau curves in multi-particle region $16m^2 \leq s, t < 36m^2$. systematically generate and select relevant graphs numerically solve associated equations for leading singularity. find an infinite sequence that accumulates at finite $s$ $t$ on physical sheet. expect such accumulations are generic $s,t > 16m^2$. Our analysis sheds new light complicated analytic structure nonperturbative relativistic amplitudes.