Random threshold conjecture for Steiner designs

Let t,k,λNt,k,\lambda\in\mathbb N with k>tk>t, let VV be an nn-element set satisfying the divisibility conditions (kiti)λ(niti)\binom{k-i}{t-i}\mid\lambda\binom{n-i}{t-i} for every i{0}[t1]i\in\{0\}\cup[t-1], and let A\mathcal A consist of independently selected kk-sets from (Vk)\binom Vk, each included with probability pp. A tt-(n,k,λ)(n,k,\lambda) design is a pair (V,B)(V,\mathcal B) with B(Vk)\mathcal B\subseteq\binom Vk such that every tt-set is contained in exactly λ\lambda members of B\mathcal B. Random design threshold conjecture. If p=ω(logn/nkt)p=\omega(\log n/n^{k-t}), then with probability tending to one there exists a tt-(n,k,λ)(n,k,\lambda) design (V,B)(V,\mathcal B) with BA\mathcal B\subseteq\mathcal A. The conjecture asserts that the threshold is governed by the requirement that every tt-set be covered at least λ\lambda times.

Sources & referencesView supporting material

Primary source

Dong Yeap Kang, Tom Kelly, Daniela Kühn, Abhishek Methuku and Deryk Osthus, “Thresholds for Latin squares and Steiner triple systems: Bounds within a logarithmic factor”, arXiv:2206.14472 (2023).

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