Doubly connected graphs with arbitrarily close hot spots conjecture

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Let ϵ>0\epsilon>0. A doubly connected metric graph is a graph of the type specified in the paper's location discussion. Let diam⁡γ\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

diam⁡γ=1,\operatorname{diam}\gamma=1,

mu2(γ)mu_2(\gamma) is simple, and

max{dist⁡(x,y):x,y∈M}<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.

References

Primary source

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

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