Asymmetric Ramsey numbers of trees
Fuente:
arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866915626977591296 |
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| author | Yan, Jun |
| author_facet | Yan, Jun |
| contents | Let $n\geqν$, let $T$ be an $n$-vertex tree with bipartition class sizes $t_1\geq t_2$, and let $S$ be a $ν$-vertex tree with bipartition class sizes $τ_1\geqτ_2$. Using four natural constructions, we show that the Ramsey number $R(T,S)$ is lower bounded by $\underline{R}(T,S)=\max\{n+τ_2,ν+\min\{t_2,ν\},\min\{2t_1,2ν\},2τ_1\}-1$.
Our main result shows that there exists a constant $c>0$, such that for all sufficiently large integers $n\geqν$, if (i) $Δ(T)\leq cn/\log n$ and $Δ(S)\leq cν/\logν$, (ii) $τ_2\geq t_2$, and (iii) $ν\geq t_1$, then $R(T,S)=\underline{R}(T,S)$. In particular, this determines the exact Ramsey numbers for a large family of pairs of trees. We also provide examples showing that $R(T,S)$ can exceed $\underline{R}(T,S)$ if any one of the three assumptions (i), (ii), and (iii) is removed. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_15673 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Asymmetric Ramsey numbers of trees Yan, Jun Combinatorics 05D10, 05C05 Let $n\geqν$, let $T$ be an $n$-vertex tree with bipartition class sizes $t_1\geq t_2$, and let $S$ be a $ν$-vertex tree with bipartition class sizes $τ_1\geqτ_2$. Using four natural constructions, we show that the Ramsey number $R(T,S)$ is lower bounded by $\underline{R}(T,S)=\max\{n+τ_2,ν+\min\{t_2,ν\},\min\{2t_1,2ν\},2τ_1\}-1$. Our main result shows that there exists a constant $c>0$, such that for all sufficiently large integers $n\geqν$, if (i) $Δ(T)\leq cn/\log n$ and $Δ(S)\leq cν/\logν$, (ii) $τ_2\geq t_2$, and (iii) $ν\geq t_1$, then $R(T,S)=\underline{R}(T,S)$. In particular, this determines the exact Ramsey numbers for a large family of pairs of trees. We also provide examples showing that $R(T,S)$ can exceed $\underline{R}(T,S)$ if any one of the three assumptions (i), (ii), and (iii) is removed. |
| title | Asymmetric Ramsey numbers of trees |
| topic | Combinatorics 05D10, 05C05 |
| url | https://arxiv.org/abs/2511.15673 |