The spectral extremal conjecture for bowties with q added edges

Let Tn,2T_{n,2} be the balanced complete bipartite graph on nn vertices, and let Yn,2,qY_{n,2,q} be obtained from Tn,2T_{n,2} by embedding qq pairwise disjoint edges into the vertex part of size n/2\lceil n/2\rceil. Let λ(G)\lambda(G) denote the spectral radius, and let a bowtie be the graph consisting of two triangles sharing one vertex.

Spectral bowtie conjecture. For q3q\ge 3, if GG is a graph of sufficiently large order nn satisfying

λ(G)λ(Yn,2,q),\lambda(G)\ge\lambda(Y_{n,2,q}),

then GG has at least

(q2)n2{q\choose 2}\left\lfloor\frac{n}{2}\right\rfloor

bowties, and Yn,2,qY_{n,2,q} is the unique spectral extremal graph.

This proposes a spectral analogue of the corresponding edge-extremal result for bowties when q=2q=2, extending it to arbitrary fixed q3q\ge3. The asserted uniqueness and the general spectral threshold remain open in the source.

Sources & referencesView supporting material

Primary source

Yongtao Li, Lihua Feng and Yuejian Peng, “Spectral supersaturation: Triangles and bowties”, arXiv:2407.04950 (2025).

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