English

A generalized Tur\'an problem in random graphs

Combinatorics 2019-03-20 v2

Abstract

We study the following generalization of the Tur\'an problem in sparse random graphs. Given graphs TT and HH, let ex(G(n,p),T,H)\mathrm{ex}\big(G(n,p), T, H\big) be the random variable that counts the largest number of copies of TT in a subgraph of G(n,p)G(n,p) that does not contain HH. We study the threshold phenomena arising in the evolution of the typical value of this random variable, for every HH and an arbitrary 22-balanced TT. Our results in the case when m2(H)>m2(T)m_2(H) > m_2(T) are a natural generalization of the Erd\H{o}s--Stone theorem for G(n,p)G(n,p), which was proved several years ago by Conlon and Gowers and by Schacht; the case T=KmT = K_m has been recently resolved by Alon, Kostochka, and Shikhelman. More interestingly, the case when m2(H)m2(T)m_2(H) \le m_2(T) exhibits a more complex and subtle behavior. Namely, the location(s) of the (possibly multiple) threshold(s) are determined by densities of various coverings of HH with copies of TT and the typical value(s) of ex(G(n,p),T,H)\mathrm{ex}\big(G(n,p), T, H\big) are given by solutions to deterministic hypergraph Tur\'an-type problems that we are unable to solve in full generality.

Keywords

Cite

@article{arxiv.1806.06609,
  title  = {A generalized Tur\'an problem in random graphs},
  author = {Wojciech Samotij and Clara Shikhelman},
  journal= {arXiv preprint arXiv:1806.06609},
  year   = {2019}
}
R2 v1 2026-06-23T02:32:59.375Z