The relativized Alon conjecture for random graph covers

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Let BB be a fixed graph, let B^\widehat B be its universal cover, and let AB^A_{\widehat B} be the adjacency operator on B^\widehat B. Let Cn(B)\mathcal{C}_n(B) denote the model of degree-nn covering graphs of BB, and let ρBnew(AG)\rho^{\mathrm{new}}_B(A_G) be the new adjacency spectral radius of a cover GG relative to BB. The relativized Alon conjecture. For every ϵ>0\epsilon>0,

Pr⁡G∈Cn(B)[ρBnew(AG)≥ρ(AB^)+ϵ]⟶0\Pr_{G\in\mathcal{C}_n(B)}\left[\rho^{\mathrm{new}}_B(A_G)\ge \rho(A_{\widehat B})+\epsilon\right]\longrightarrow 0

as n→∞n\to\infty. This asserts that the new spectrum of a random high-degree cover is asymptotically bounded by the spectral radius of the universal cover. The source attributes the conjecture to earlier work and presents results toward it; no resolution is supplied here.

References

Primary source

Joel Friedman and David-Emmanuel Kohler, “The Relativized Second Eigenvalue Conjecture of Alon”, arXiv:1403.3462 (2014).

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