English

Simultaneously nonvanishing higher derived limits

Logic 2024-11-26 v1 Algebraic Topology Category Theory

Abstract

The derived functors limn\lim^n of the inverse limit find many applications in algebra and topology. In particular, the vanishing of certain derived limits limnA[H]\lim^n \mathbf{A}[H], parametrized by an abelian group HH, has implications for strong homology and condensed mathematics. In this paper, we prove that if d=ωn\mathfrak{d}=\omega_n, then limnA[H]0\lim^n \mathbf{A}[H] \neq 0 holds for H=Z(ωn)H=\mathbb{Z}^{(\omega_n)} (i.e. the direct sum of ωn\omega_n-many copies of Z\mathbb{Z}). The same holds for H=ZH=\mathbb{Z} under the assumption that w(Skk+1)\mathrm{w}\diamondsuit(S^{k+1}_k) holds for all k<nk < n. In particular, this shows that if limnA[H]=0\lim^n \mathbf{A}[H] = 0 holds for all n1n \geq 1 and all abelian groups HH, then 20ω+12^{\aleph_0} \geq \aleph_{\omega+1}, thus answering a question of Bannister. Finally, we prove some consistency results regarding simultaneous nonvanishing of derived limits, again in the case of H=ZH = \mathbb{Z}. In particular, we show the consistency, relative to ZFC\mathsf{ZFC}, of 2k<ωlimkA0\bigwedge_{2 \leq k < \omega} \lim^k \mathbf{A} \neq 0.

Keywords

Cite

@article{arxiv.2411.15856,
  title  = {Simultaneously nonvanishing higher derived limits},
  author = {Matteo Casarosa and Chris Lambie-Hanson},
  journal= {arXiv preprint arXiv:2411.15856},
  year   = {2024}
}

Comments

31 pages

R2 v1 2026-06-28T20:10:31.698Z