Title:Exact threshold and lognormal limit for non-linear Hamilton cycles

Abstract:For positive integers $r > \ell \geq 1$, an $\ell$-cycle in an $r$-uniform hypergraph is a cycle where each edge consists of $r$ vertices and each pair of consecutive edges intersect in $\ell$ vertices. We show that for $\ell \geq 2$, a random $r$-uniform hypergraph contains a Hamilton $\ell$-cycle with high probability whenever the expected number of such cycles tends to infinity. Moreover, for $\ell = 2$, we show that the normalized number of Hamilton $2$-cycles converges to a lognormal distribution. This determines the exact threshold for the appearance of non-linear Hamilton cycles in random hypergraphs, confirming a conjecture of Narayanan and Schacht.