English

Elementary embeddings into ultrapower $\mathrm{II}_1$ factors without a UCP lift

Operator Algebras 2025-12-12 v1 Logic

Abstract

We show that there are II1\mathrm{II}_1 factors MM and elementary embeddings MMUM \to M^{\mathcal{U}} which do not lift to sequences of UCP maps, and in fact MM can be chosen from any given elementary equivalence class. Furthermore, under continuum hypothesis, we show that in the sense of cardinality "most" automorphisms of a ultrapower MUM^{\mathcal{U}} of a separable II1\mathrm{II}_1 factor do not lift to a sequence of UCP maps φn:MM\varphi_n: M \to M.

Keywords

Cite

@article{arxiv.2512.10129,
  title  = {Elementary embeddings into ultrapower $\mathrm{II}_1$ factors without a UCP lift},
  author = {David Gao and David Jekel},
  journal= {arXiv preprint arXiv:2512.10129},
  year   = {2025}
}

Comments

8 pages. Comments welcome