The distance-t chromatic index of graphs

TL;DR

This paper establishes new upper bounds for the distance-t chromatic index of graphs, showing it can be bounded by a linear function of ^t and by ^t/\,log  for graphs with certain properties, extending previous results.

Contribution

It provides two novel upper bounds for the distance-t chromatic index, one analogous to known bounds for strong chromatic index, and the other tight up to a constant factor for graphs with large girth.

Findings

Bound of (2-)^t for graphs with maximum degree 

Bound of O(^t/ ) for graphs with girth at least 2t+1

The second bound is tight up to a constant factor for certain graphs

Abstract

We consider two graph colouring problems in which edges at distance at most $t$ are given distinct colours, for some fixed positive integer $t$. We obtain two upper bounds for the distance-$t$ chromatic index, the least number of colours necessary for such a colouring. One is a bound of $(2-\eps)\Delta^t$ for graphs of maximum degree at most $\Delta$, where $\eps$ is some absolute positive constant independent of $t$. The other is a bound of $O(\Delta^t/\log \Delta)$ (as $\Delta\to\infty$) for graphs of maximum degree at most $\Delta$ and girth at least $2t+1$. The first bound is an analogue of Molloy and Reed's bound on the strong chromatic index. The second bound is tight up to a constant multiplicative factor, as certified by a class of graphs of girth at least $g$, for every fixed $g \ge 3$, of arbitrarily large maximum degree $\Delta$, with distance-$t$ chromatic index at least $\Omega(\Delta^t/\log \Delta)$.