Vector-field expansion conjecture for arborescence ratios

Let Γ\Gamma be a graph and let Γ~\tilde{\Gamma} be a kk-fold cover of Γ\Gamma. Let V\mathcal V be the set of vector fields of Γ\Gamma, let wt(γ)\operatorname{wt}(\gamma) denote the weight of a vector field, and let ff be a function from Vk1\mathcal V^{k-1} to Z0\mathbb Z_{\geq 0}. Vector-field expansion conjecture. The arborescence ratio satisfies

Av~(Γ~)Av~(Γ)=(γ1,,γk1)Vk1f(γ1,,γk1)i=1k1wt(γi).\frac{A_{\tilde v}(\tilde\Gamma)}{A_{\tilde v}(\Gamma)}=\sum_{(\gamma_1,\ldots,\gamma_{k-1})\in\mathcal V^{k-1}}f(\gamma_1,\ldots,\gamma_{k-1})\prod_{i=1}^{k-1}\operatorname{wt}(\gamma_i).

The conjecture proposes a nonnegative expansion in products of k1k-1 weighted vector fields. The source presents this as a potential combinatorial interpretation of the arborescence ratio; no general proof or resolution is supplied, and the denominator is written with Av~(Γ)A_{\tilde v}(\Gamma) in the source.

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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