English

Ring isomorphisms in norm between Banach algebras of continuous complex-valued functions

Functional Analysis 2026-01-19 v1

Abstract

Let XX and YY be compact Hausdorff spaces, and let C(X)C(X) and C(Y)C(Y) denote the commutative Banach algebras of all continuous complex-valued functions on XX and YY, respectively. We study bijective maps TT from C(X)C(X) onto C(Y)C(Y) which preserve the ring structure in the norm in the following sense: T(f+g)=T(f)+T(g),T(fg)=T(f)T(g)(f,gC(X)). \|T(f+g)\|=\|T(f)+T(g)\|,\quad \|T(fg)\|=\|T(f)T(g)\| \qquad(f,g\in C(X)). Our main objective is to clarify whether such maps must necessarily be induced by homeomorphisms between the underlying spaces. Under the additional assumption that T(f)=T(f)T(\overline{f})=\overline{T(f)} for fC(X)f\in C(X), we prove that TT is a real-linear isometry. As a consequence, we obtain a concrete representation of such maps as weighted composition operators.

Keywords

Cite

@article{arxiv.2601.11165,
  title  = {Ring isomorphisms in norm between Banach algebras of continuous complex-valued functions},
  author = {T. Miura and T. Takahashi},
  journal= {arXiv preprint arXiv:2601.11165},
  year   = {2026}
}