Star decomposition threshold conjecture for random regular graphs

Let d3d\geq 3, let GN,d\mathcal{G}_{N,d} be a uniformly random dd-regular graph on NN vertices, and let kdind=κd(αd)k_d^{\mathrm{ind}}=\lfloor\kappa_d(\alpha_d^\star)\rfloor, where αd\alpha_d^\star is the limiting independence ratio of GN,d\mathcal{G}_{N,d}. A kk-star decomposition partitions the edges into stars with kk edges each. Star decomposition threshold conjecture. If

d/2<kkdind,d/2<k\leq k_d^{\mathrm{ind}},

then GN,d\mathcal{G}_{N,d} a.a.s. has a kk-star decomposition as NN\to\infty whenever NdNd is divisible by 2k2k, apart from d=5d=5 and perhaps a small number of further exceptional degrees. The conjecture asserts that the independent-set obstruction is essentially the only restriction, connecting star decompositions with the extremal independent-set problem in random regular graphs; its status is unresolved in the supplied text.

Sources & referencesView supporting material

Primary source

Viktor Harangi, “Star decompositions and independent sets in random regular graphs”, arXiv:2503.09458 (2025).

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