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arXiv · 2106.15464

Degrees in link graphs of regular graphs

Itai Benjamini·John Haslegrave
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Abstract

We analyse an extremal question on the degrees of the link graphs of a finite regular graph, that is, the subgraphs induced by non-trivial spheres. We show that if $G$ is $d$-regular and connected but not complete then some link graph of $G$ has minimum degree at most $\lfloor 2d/3\rfloor-1$, and if $G$ is sufficiently large in terms of $d$ then some link graph has minimum degree at most $\lfloor d/2\rfloor-1$; both bounds are best possible. We also give the corresponding best-possible result for the corresponding problem where subgraphs induced by balls, rather than spheres, are considered. We motivate these questions by posing a conjecture concerning expansion of link graphs in large bounded-degree graphs, together with a heuristic justification thereof.

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Itai Benjamini, John Haslegrave. 2022-04-05. Degrees in link graphs of regular graphs. https://doi.org/10.37236/10561

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