Ramsey-Turán theory for partially-ordered sets

Abstract

We introduce weak and strong poset Ramsey-Turán numbers for $t$-chains in host poset families, focusing on the Boolean lattice family $\mathcal{B}=\{B_n:n\ge 1\}$. For any poset $P$, we show $\mathrm{RT}(\mathcal{B};n,P,l,t)\le {\mathrm{RT}}^{♯}(\mathcal{B};n,P,l,t)$, with equality when $P$ is a chain. In particular, for $t=1$, $\mathrm{RT}(\mathcal{B};n,C_k,l)={\mathrm{RT}}^{♯}(\mathcal{B};n,C_k,l)=(k-1)(l-1)$. We also give universal upper bounds for both versions. For fixed $k,l,t$ with $\min \{l-1,k-1\}\ge 1$, we prove ${\mathrm{RT}}^{♯}(\mathcal{B};n,A_k,l,t)=\hat{I}˜(n^t)$. More generally, for every non-chain poset $P$, the strong number is $\hat{I}˜(n^t)$ for fixed $l,t$. Finally, if $h(P)=r>t$ and $l(n)=\lfloor M_n^2\rfloor$ with $0<{\hat{I}}^2\le \hat{I}\pm <1$, then both weak and strong versions admit lower bounds of order $\hat{I}\text{c◯}\left(2^{{\hat{I}}^{2}n}{n}^{-{\hat{I}}^2/2}\right)$.

22 pages