On Matoušek-like Embedding Obstructions of Countably Branching Graphs

Abstract: In this paper we present new proofs of the non-embeddability of countably branching trees into Banach spaces satisfying property $(\beta_p)$ and of countably branching diamonds into Banach spaces which are $p$-AMUC for $p > 1$. These proofs are entirely metric in nature and are inspired by previous work of Ji\v{r}\'i Matou\v{s}ek. In addition, using this metric method, we succeed in extending these results to metric spaces satisfying certain curvature-like inequalities. Finally, we extend an embedding result of Tessera to give lower bounds on the compression for a class of Lipschitz embeddings of the countably branching trees into Banach spaces containing $\ell_p$-asymptotic models for $p \geq 1$.