Random-cover expectation conjecture for arborescence ratios

Let Γ=(E,V)\Gamma=(E,V) be a graph, fix a vertex vv with non-trivial arborescence, and let V\mathcal V be the set of vector fields of Γ\Gamma. Let Γ\Gamma' be a uniformly random kk-fold cover of Γ\Gamma. Random-cover expectation conjecture. The expected arborescence ratio is

E[Av(Γ)Av(Γ)]=1k(γVwt(γ))k1=1kwV(αEs(w)wt(α))k1.\mathbb E\left[\frac{\mathcal A_{v'}(\Gamma')}{\mathcal A_v(\Gamma)}\right]=\frac{1}{k}\left(\sum_{\gamma\in\mathcal V}\operatorname{wt}(\gamma)\right)^{k-1}=\frac{1}{k}\prod_{w\in V}\left(\sum_{\alpha\in E_s(w)}\operatorname{wt}(\alpha)\right)^{k-1}.

This conjecture is motivated by the claim that, over all kk-fold covers, the ratios exhaust all possible (k1)(k-1)-tuples of vector fields. That exhaustion is known only in the 2-fold case, leaving the general random-cover expectation open.

Sources & referencesView supporting material

Primary source

Sunita Chepuri, CJ Dowd, Andy Hardt, Gregory Michel, Sylvester W. Zhang and Valerie Zhang, “Arborescences of Covering Graphs”, arXiv:1912.01060 (2021).

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