Alon–Spencer's clique-packing conjecture for random graphs

Let GG be the random graph Gn,1/2G_{n,1/2}. Define f(k)=(nk)2(k2)f(k)={n\choose k}2^{-\binom{k}{2}}, let

k0=min{k:f(k)<1},k_0=\min\{k:f(k)<1\},

and set k=k04k=k_0-4. A packing is a collection of edge-disjoint cliques, and let νk(G)\nu_k(G) denote the maximum size of a packing of kk-cliques in GG. Since

νk(G)(n2)(k2),\nu_k(G)\leq \frac{{n\choose 2}}{{k\choose 2}},

Alon–Spencer's conjecture. The trivial upper bound gives the true order of magnitude of the expected packing number:

Eνk(G)=Ω(n2/k2).\mathbb{E}\nu_k(G)=\Omega(n^2/k^2).

This conjecture predicts that a random graph typically admits a packing of a constant-order fraction of the maximum possible number of edge-disjoint kk-cliques. The paper's abstract states that this conjecture is false, so the conjecture is refuted.

Sources & referencesView supporting material

Primary source

Huseyin Acan and Jeff Kahn, “Disproof of a packing conjecture of Alon and Spencer”, arXiv:1706.01866 (2017).

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