Integral representations of projective norm-attaining tensors

TL;DR

This paper introduces a measure-theoretic approach to projective norm attainment in tensor products of Banach spaces, establishing approximation results, density equivalences, and examples of non-norm-attaining tensors.

Contribution

It develops the concept of integral projective norm-attaining tensors using Bochner integrals, broadening the framework for studying norm attainment in tensor products.

Findings

Every integral norm-attaining tensor can be approximated by finite representation tensors.

The density problem for classical norm-attaining tensors is equivalent to that for integral tensors.

Certain tensor products contain non-norm-attaining tensors, extending previous constructions.

Abstract

We introduce a Bochner integral approach to projective norm attainment in tensor products of Banach spaces by defining the class of integral projective norm-attaining tensors. This framework provides a broader, measure-theoretic approach to the study of projective norm attainment in tensor products of Banach spaces. We show that every integral norm-attaining tensor can be approximated in norm by norm-attaining tensors with finite representations. As a consequence, the Bishop-Phelps type density problem for classical norm-attaining tensors is equivalent to the corresponding density problem for integral norm-attaining tensors. Moreover, we prove that if an integral projective norm-attaining tensor represented by a Radon measure is an extreme point, then it must be an elementary tensor. We further investigate weaker topological versions of integral norm-attainment, including weak and weak$^*$ integral representations, providing sufficient conditions for the existence of Bochner representations. Finally, we extend known constructions of projective tensor products containing non-norm-attaining tensors to the integral setting. We show, for instance, that $L_1\widehat{\otimes}_\pi L_p$ and the real $c_0\widehat{\otimes}_\pi L_p$ contain non-norm-attaining tensors for $1<p<\infty$.