H-free extension of Brouwer's Laplacian eigenvalue-sum conjecture

Let k1k\ge 1, let HH be a graph, and let ex(n;H)\operatorname{ex}(n;H) denote the maximum number of edges in an nn-vertex HH-free graph. For a graph G=(V,E)G=(V,E), define

εk(G)=i=1kλi(L(G))E.\operatorname{\varepsilon}_k(G)=\sum_{i=1}^k\lambda_i(L(G))-|E|.

H-free Brouwer conjecture. For every HH-free graph G=(V,E)G=(V,E) with Vk|V|\ge k,

εk(G)ex(k+1;H).\operatorname{\varepsilon}_k(G)\le \operatorname{ex}(k+1;H).

The paper notes that the proposed bound is sharp, using an (k+1)(k+1)-vertex extremal HH-free graph together with isolated vertices. The supplied status does not indicate whether the conjecture is resolved.

Sources & referencesView supporting material

Primary source

Alan Lew, “An approximate version of Brouwer's Laplacian conjecture”, arXiv:2601.17575 (2026).

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