English

Operational 2-local automorphisms/derivations

Operator Algebras 2024-07-16 v1 Functional Analysis

Abstract

Let ϕ:AA\phi: A\to A be a (not necessarily linear, additive or continuous) map of a standard operator algebra. Suppose for any a,bAa,b\in A there is an algebra automorphism θa,b\theta_{a,b} of A A such that \begin{align*} \phi(a)\phi(b) = \theta_{a,b}(ab). \end{align*} We show that either ϕ\phi or ϕ-\phi is a linear Jordan homomorphism. Similar results are obtained when any of the following conditions is satisfied: \begin{align*} \phi(a) + \phi(b) &= \theta_{a,b}(a+b), \\ \phi(a)\phi(b)+\phi(b)\phi(a) &= \theta_{a,b}(ab+ba), \quad\text{or} \\ \phi(a)\phi(b)\phi(a) &= \theta_{a,b}(aba). \end{align*} We also show that a map ϕ:MM\phi: M\to M of a semi-finite von Neumann algebra M M is a linear derivation if for every a,bMa,b\in M there is a linear derivation Da,bD_{a,b} of MM such that ϕ(a)b+aϕ(b)=Da,b(ab). \phi(a)b + a\phi(b) = D_{a,b}(ab).

Keywords

Cite

@article{arxiv.2407.10150,
  title  = {Operational 2-local automorphisms/derivations},
  author = {Liguang Wang and Ngai-Ching Wong},
  journal= {arXiv preprint arXiv:2407.10150},
  year   = {2024}
}

Comments

10 pages; to appear in J. Nonlinear and Convex Analysis

R2 v1 2026-06-28T17:40:13.983Z