Compactness of products and commutators of inner projections
Functional Analysis
2026-04-28 v2
Abstract
In this paper, we study the compactness of the product and the commutator of two inner projections on the Hardy spaces over the unit disk and the polydisc. For the single-variable case, we provide a complete characterization of the compactness of the commutator of two inner projections by means of Douglas algebra. In the multivariable setting, we discover a rigidity phenomenon: on the bidisc, the product of two inner projections is compact if and only if it has finite rank, whereas on the polydisc of dimension strictly greater than two, any such compact product must be trivial.
Cite
@article{arxiv.2604.22284,
title = {Compactness of products and commutators of inner projections},
author = {Peiran Zhang and Roumei Tian and Yufeng Lu and Yixin Yang and Chao Zu},
journal= {arXiv preprint arXiv:2604.22284},
year = {2026}
}