English

Higher derivatives of operator functions in ideals of von Neumann algebras

Operator Algebras 2023-12-27 v3 Functional Analysis

Abstract

Let M\mathscr{M} be a von Neumann algebra and aa be a self-adjoint operator affiliated with M\mathscr{M}. We define the notion of an "integral symmetrically normed ideal" of M\mathscr{M} and introduce a space OC[k](R)Ck(R)OC^{[k]}(\mathbb{R}) \subseteq C^k(\mathbb{R}) of functions RC\mathbb{R} \to \mathbb{C} such that the following result holds: for any integral symmetrically normed ideal I\mathscr{I} of M\mathscr{M} and any fOC[k](R)f \in OC^{[k]}(\mathbb{R}), the operator function Isabf(a+b)f(a)I\mathscr{I}_{\mathrm{sa}} \ni b \mapsto f(a+b)-f(a) \in \mathscr{I} is kk-times continuously Fr\'{e}chet differentiable, and the formula for its derivatives may be written in terms of multiple operator integrals. Moreover, we prove that if fB˙11,(R)B˙1k,(R)f \in \dot{B}_1^{1,\infty}(\mathbb{R}) \cap \dot{B}_1^{k,\infty}(\mathbb{R}) and ff' is bounded, then fOC[k](R)f \in OC^{[k]}(\mathbb{R}). Finally, we prove that all of the following ideals are integral symmetrically normed: M\mathscr{M} itself, separable symmetrically normed ideals, Schatten pp-ideals, the ideal of compact operators, and -- when M\mathscr{M} is semifinite -- ideals induced by fully symmetric spaces of measurable operators.

Keywords

Cite

@article{arxiv.2107.03693,
  title  = {Higher derivatives of operator functions in ideals of von Neumann algebras},
  author = {Evangelos A. Nikitopoulos},
  journal= {arXiv preprint arXiv:2107.03693},
  year   = {2023}
}

Comments

43 pages. This version has been updated to match the published version, aside from the inclusion of a sketch of proof of Proposition 2.2.8 (omitted from the published version), the correction of some typos, and the adjustment of some references