Explicit perfect-matching threshold conjecture for randomly perturbed unbalanced complete bipartite graphs

Let α(0,1/2)\alpha\in(0,1/2) be fixed and let d=αnd=\alpha n. For p=C/np=C/n, define γ\gamma_* as the smallest root of

x=(1α)Cexp((1α)Cex),x=(1-\alpha)C\exp\bigl(-(1-\alpha)C\mathrm{e}^{-x}\bigr),

and define γ=(1α)Ceγ\gamma^*=(1-\alpha)C\mathrm{e}^{-\gamma_*}. The constant C=C(α)C=C(\alpha) is the solution of

1γ+γ+γγ(22α)C=12α22α.1-\frac{\gamma_*+\gamma^*+\gamma_*\gamma^*}{(2-2\alpha)C}=\frac{1-2\alpha}{2-2\alpha}.

Perfect-matching threshold conjecture. The sharp dd-threshold for containing a perfect matching is C/nC/n.

The formula comes from the asymptotic size of the largest matching in a sparse random graph, applied to G(nd,p)G(n-d,p). It gives an explicit prediction for the threshold that the preceding reduction identifies, but the paper does not prove it.

Sources & referencesView supporting material

Primary source

Alberto Espuny Díaz and Richarlotte Valérà Razafindravola, “How many random edges make an almost-Dirac graph Hamiltonian?”, arXiv:2410.14447 (2024).

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