English

Grothendieck ideals of $\ell_\infty$

Functional Analysis 2026-07-27 v1

Abstract

We answer several questions in the literature concerning the Grothendieck property of ideals of the Banach lattice \ell_\infty that contain c0c_0. Any such ideal can be represented as a space c0,Ic_{0,\mathcal I} for I\mathcal I an ideal over the natural numbers. We provide a characterization of when c0,Ic_{0,\mathcal I} is a Grothendieck space in terms of finitely additive measures over P(ω)\mathcal P(\omega) and elements of I\mathcal I. Using this characterization we show that there are analytic ideals I\mathcal I such that c0,Ic_{0,\mathcal I} is Grothendieck. In the opposite direction we show that for any AD family A\mathcal A, c0,I(A)c_{0,\mathcal I(\mathcal A)} and C(KA)C(K_\mathcal A) are not Grothendieck spaces, and that for most of the Borel ideals present in the literature, c0,Ic_{0,\mathcal I} is not Grothendieck. In particular, the family of ideals that do not have the Grothendieck property is cofinal in the Rudin-Keisler order, so the Grothendieck property is not downward closed in the Kat\v{e}tov order. Continuing the work in \cite{Sobota-Zuchowski, Zuchowski}, we also provide similar results on the Nikodym property of the Boolean subalgebras of P(ω)\mathcal P(\omega) generated by the ideal I\mathcal I.

Keywords

Cite

@article{arxiv.2607.25095,
  title  = {Grothendieck ideals of $\ell_\infty$},
  author = {Michael Hrusák and Michael A. Rincón-Villamizar and Luis Sáenz and Carlos Uzcátegui Aylwin},
  journal= {arXiv preprint arXiv:2607.25095},
  year   = {2026}
}