English

Thresholds vs. expectation thresholds for non-spanning graphs

Combinatorics 2026-02-03 v1

Abstract

The threshold pc(H)p_c(H) for the event that the binomial random graph Gn,pG_{n,p} contains a copy of a graph HH is the unique pp for which P(HGn,p)=1/2\mathbb{P}(H \subseteq G_{n,p}) = 1/2, and the fractional expectation threshold qf(H)q_f(H) is roughly the best lower bound on pc(H)p_c(H) using simple expectation considerations. All previously known HH's with pc(H)p_c(H) substantially larger than qf(H)q_f(H) have the property that vH>n/2v_H > n/2 (where vHv_H is the number of vertices of HH). We construct small graphs whose threshold for containment in Gn,pG_{n,p} is of different order than their corresponding fractional expectation threshold: there is a constant c>0c > 0 such that for any m  (n)m \; (\leq n), there is a graph HH with vH=mv_H = m and pc(H)>qf(H)clog1/2(vH).p_c(H) > q_f(H) c \log^{1/2}(v_H).

Keywords

Cite

@article{arxiv.2602.00278,
  title  = {Thresholds vs. expectation thresholds for non-spanning graphs},
  author = {Quentin Dubroff},
  journal= {arXiv preprint arXiv:2602.00278},
  year   = {2026}
}
R2 v1 2026-07-01T09:28:42.387Z