Beyond the MaxCut problem in $H$-free graphs
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arXiv
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| Autori principali: | , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866908454974652416 |
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| author | Jin, Zhihan Milojević, Aleksa Tomon, István |
| author_facet | Jin, Zhihan Milojević, Aleksa Tomon, István |
| contents | In a recent breakthrough, Zhang proves that if $G$ is an $H$-free graph with $m$ edges, then $G$ has a cut of size at least $m/2+c_Hm^{0.5001}$, making a significant step towards a well known conjecture of Alon, Bollobás, Krivelevich and Sudakov. We show that the methods of Zhang can be further boosted, and prove the following strengthening. If $G$ is a graph with $m$ edges and no clique of size $m^{1/2-δ}$, then $G$ has a cut of size at least $m/2+m^{1/2+\varepsilon}$ for some $\varepsilon=\varepsilon(δ)>0$.
In addition, we sharpen another result of Zhang by proving that if $G$ is an $n$-vertex $m$-edge graph with MaxCut of size at most $m/2+n^{1+\varepsilon}$ (or its smallest eigenvalue $λ_n$ satisfies $|λ_n|\leq n^{\varepsilon}$), then $G$ is $n^{-\varepsilon}$-close to the disjoint union of cliques for some absolute constant $\varepsilon>0$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_13298 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Beyond the MaxCut problem in $H$-free graphs Jin, Zhihan Milojević, Aleksa Tomon, István Combinatorics In a recent breakthrough, Zhang proves that if $G$ is an $H$-free graph with $m$ edges, then $G$ has a cut of size at least $m/2+c_Hm^{0.5001}$, making a significant step towards a well known conjecture of Alon, Bollobás, Krivelevich and Sudakov. We show that the methods of Zhang can be further boosted, and prove the following strengthening. If $G$ is a graph with $m$ edges and no clique of size $m^{1/2-δ}$, then $G$ has a cut of size at least $m/2+m^{1/2+\varepsilon}$ for some $\varepsilon=\varepsilon(δ)>0$. In addition, we sharpen another result of Zhang by proving that if $G$ is an $n$-vertex $m$-edge graph with MaxCut of size at most $m/2+n^{1+\varepsilon}$ (or its smallest eigenvalue $λ_n$ satisfies $|λ_n|\leq n^{\varepsilon}$), then $G$ is $n^{-\varepsilon}$-close to the disjoint union of cliques for some absolute constant $\varepsilon>0$. |
| title | Beyond the MaxCut problem in $H$-free graphs |
| topic | Combinatorics |
| url | https://arxiv.org/abs/2507.13298 |