Jiang et al.'s forbidden-subgraph multiplicity conjecture

From papers

Let λ>0\lambda>0 and pN+p\in\mathbb{N}^+. For a finite family F\mathcal{F} of signed graphs, let Mp,F(λ,N)M_{p,\mathcal{F}}(\lambda,N) be the maximum of mult(λ,G)\operatorname{mult}(-\lambda,G) over all pp-colorable signed graphs GG on at most NN vertices that contain no member of F\mathcal{F} as an induced subgraph and satisfy λp+1(G)λ\lambda_{p+1}(G)\geq-\lambda, where λp+1(G)\lambda_{p+1}(G) is the (p+1)(p+1)-st smallest eigenvalue of GG. Jiang et al.'s forbidden-subgraph conjecture. For every λ>0\lambda>0 and pN+p\in\mathbb{N}^+, there exists a finite family F\mathcal{F} of signed graphs such that λ1(F)<λ\lambda_1(F)<-\lambda for every FFF\in\mathcal{F} and

Mp,F(λ,N){N/kp(λ)+o(N)if kp(λ)<,o(N)otherwise.M_{p,\mathcal{F}}(\lambda,N)\leq \begin{cases} N/k_p(\lambda)+o(N) & \text{if }k_p(\lambda)<\infty,\\ o(N) & \text{otherwise}. \end{cases}

This conjecture is the forbidden-subgraph estimate underlying the proposed asymptotic formula for Nα,β(d)N_{\alpha,\beta}(d). The supplied context does not report a resolution, so the general assertion remains open.

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Sources & referencesView supporting material

Primary source

Zilin Jiang and Zhiyu Wang, “On the smallest eigenvalues of 3-colorable graphs”, arXiv:2505.03014 (2025).

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