Doubly connected graphs with arbitrarily close hot spots conjecture

Let ϵ>0\epsilon>0. A doubly connected metric graph is a graph of the type specified in the paper's location discussion. Let diamγ\operatorname{diam}\gamma denote its diameter, μ2(γ)\mu_2(\gamma) its second eigenvalue, and MM its hot-spot set.

Close hot-spots conjecture. For every ϵ>0\epsilon>0, there exists a doubly connected graph γ\gamma such that

diamγ=1,\operatorname{diam}\gamma=1,

mu2(γ)mu_2(\gamma) is simple, and

max{dist(x,y):x,yM}<ϵ.{\text{\rm max}}\{\operatorname{dist}(x,y):x,y\in M\}<\epsilon.

This shows that even without a tree-like boundary structure, the hot spots may be arbitrarily close relative to the graph diameter. The source gives no resolution status.

Sources & referencesView supporting material

Primary source

James B. Kennedy and Jonathan Rohleder, “On the hot spots of quantum graphs”, arXiv:2003.14335 (2021).

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