Powers of Hamiltonian cycles in randomly augmented P\'osa-Seymour graphs

TL;DR

This paper investigates the minimum number of random edges needed to ensure the presence of the m-th power of a Hamiltonian cycle in Pósa-Seymour graphs, revealing threshold behaviors and providing tight bounds.

Contribution

It introduces asymptotically tight bounds on over-thresholds for adding random edges to Pósa-Seymour graphs to guarantee Hamiltonian cycle powers, including for specific small parameters.

Findings

Established asymptotically tight bounds on over-thresholds for large m.

Identified conditions where bounds coincide for infinitely many m.

Determined thresholds for small values of k and m.

Abstract

We study the question of the least number of random edges that need to be added to a P\'osa-Seymour graph, that is, a graph with minimum degree exceeding $\frac k{k+1}n$, to secure the existence of the $m$-th power of a Hamiltonian cycle, $m>k$. It turns out that, depending on $k$ and $m$, this quantity may be captured by two types of thresholds, with one of them, called over-threshold, becoming dominant for large $m$. Indeed, for each $k\ge2$ and $m>m_0(k)$, we establish asymptotically tight lower and upper bounds on the over-thresholds (provided they exist) and show that for infinitely many instances of $m$ the two bounds coincide. In addition, we also determine the thresholds for some small values of $k$ and $m$.