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

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

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

1−γ∗+γ∗+γ∗γ∗(2−2α)C=1−2α2−2α.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(n−d,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.

References

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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