Ahanjideh–Akbari–Fakharan–Trevisan conjecture on Laplacian eigenvalues and diameter

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Let GG be a connected graph of order nn, let dd be its diameter with d≥2d\ge 2, and let mGIm_GI denote the number of Laplacian eigenvalues of GG in an interval I⊆[0,n]I\subseteq[0,n]. The path on d+1d+1 vertices is denoted by Pd+1P_{d+1}. Ahanjideh–Akbari–Fakharan–Trevisan conjecture. If G≠Pd+1G\ne P_{d+1}, then

mG[n−d+2,n]≤n−d.m_G[n-d+2,n]\le n-d.

This conjecture concerns the distribution of Laplacian eigenvalues of connected graphs in relation to their diameter. The stated source notes that it was verified when d∈{2,3}d\in\{2,3\} or when the diameter is at most the independence number; its general status is not specified here.

References

Primary source

Leyou Xu and Bo Zhou, “Proof of a conjecture on distribution of Laplacian eigenvalues and diameter, and beyond”, arXiv:2303.11503 (2023).

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