English

Seymour's Second Neighborhood Conjecture for orientations of (pseudo)random graphs

Combinatorics 2022-11-15 v1

Abstract

Seymour's Second Neighborhood Conjecture (SNC) states that every oriented graph contains a vertex whose second neighborhood is as large as its first neighborhood. We investigate the SNC for orientations of both binomial and pseudo random graphs, verifying the SNC asymptotically almost surely (a.a.s.) (i) for all orientations of G(n,p)G(n,p) if lim supnp<1/4\limsup_{n\to\infty} p < 1/4; and (ii) for a uniformly-random orientation of each weakly (p,Anp)(p,A\sqrt{np})-bijumbled graph of order nn and density pp, where p=Ω(n1/2)p=\Omega(n^{-1/2}) and 1p=Ω(n1/6)1-p = \Omega(n^{-1/6}) and A>0A>0 is a universal constant independent of both nn and pp. We also show that a.a.s. the SNC holds for almost every orientation of G(n,p)G(n,p). More specifically, we prove that a.a.s. (iii) for all ε>0\varepsilon > 0 and p=p(n)p=p(n) with lim supnp2/3ε\limsup_{n\to\infty} p \le 2/3-\varepsilon, every orientation of G(n,p)G(n,p) with minimum outdegree Ωε(n)\Omega_\varepsilon(\sqrt{n}) satisfies the SNC; and (iv) for all p=p(n)p=p(n), a random orientation of G(n,p)G(n,p) satisfies the SNC.

Keywords

Cite

@article{arxiv.2211.06540,
  title  = {Seymour's Second Neighborhood Conjecture for orientations of (pseudo)random graphs},
  author = {Fábio Botler and Phablo F. S. Moura and Tássio Naia},
  journal= {arXiv preprint arXiv:2211.06540},
  year   = {2022}
}

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14 pages