Quasi-Carousel Tournaments

TL;DR

This paper characterizes sequences of large tournaments that are nearly balanced in outdegree and locally transitive, by analyzing the asymptotic behavior of specific sub-tournaments and their densities.

Contribution

It introduces new characterizations of almost balanced, asymptotically locally transitive tournament sequences using quasi-random properties.

Findings

Characterizations of tournament sequences with vanishing $W_4$ and $L_4$ densities.

Connections between local transitivity and quasi-random properties.

Conditions under which large tournaments approximate locally transitive structures.

Abstract

A tournament is called locally transitive if the outneighbourhood and the inneighbourhood of every vertex are transitive. Equivalently, a tournament is locally transitive if it avoids the tournaments $W_4$ and $L_4$, which are the only tournaments up to isomorphism on four vertices containing a unique $3$-cycle. On the other hand, a sequence of tournaments $(T_n)_{n\in\mathbb{N}}$ with $|V(T_n)| = n$ is called almost balanced if all but $o(n)$ vertices of $T_n$ have outdegree $(1/2 + o(1))n$. In the same spirit of quasi-random properties, we present several characterizations of tournament sequences that are both almost balanced and asymptotically locally transitive in the sense that the density of $W_4$ and $L_4$ in $T_n$ goes to zero as $n$ goes to infinity.