English

Automatic continuity and $C_0(\Omega)$-linearity of linear maps between $C_0(\Omega)$-modules

Operator Algebras 2010-05-26 v1 Functional Analysis

Abstract

Let Ω\Omega be a locally compact Hausdorff space. We show that any local C\mathbb{C}-linear map (where "local" is a weaker notion than C0(Ω)C_0(\Omega)-linearity) between Banach C0(Ω)C_0(\Omega)-modules are "nearly C0(Ω)C_0(\Omega)-linear" and "nearly bounded". As an application, a local C\mathbb{C}-linear map θ\theta between Hilbert C0(Ω)C_0(\Omega)-modules is automatically C0(Ω)C_0(\Omega)-linear. If, in addition, Ω\Omega contains no isolated point, then any C0(Ω)C_0(\Omega)-linear map between Hilbert C0(Ω)C_0(\Omega)-modules is automatically bounded. Another application is that if a sequence of maps {θn}\{\theta_n\} between two Banach spaces "preserve c0c_0-sequences" (or "preserve ultra-c0c_0-sequences"), then θn\theta_n is bounded for large enough nn and they have a common bound. Moreover, we will show that if θ\theta is a bijective "biseparating" linear map from a "full" essential Banach C0(Ω)C_0(\Omega)-module EE into a "full" Hilbert C0(Δ)C_0(\Delta)-module FF (where Δ\Delta is another locally compact Hausdorff space), then θ\theta is "nearly bounded" (in fact, it is automatically bounded if Δ\Delta or Ω\Omega contains no isolated point) and there exists a homeomorphism σ:ΔΩ\sigma: \Delta \rightarrow \Omega such that θ(eφ)=θ(e)φσ\theta(e\cdot \varphi) = \theta(e)\cdot \varphi\circ \sigma (eE,φC0(Ω)e\in E, \varphi\in C_0(\Omega)).

Keywords

Cite

@article{arxiv.1005.4561,
  title  = {Automatic continuity and $C_0(\Omega)$-linearity of linear maps between $C_0(\Omega)$-modules},
  author = {Chi-Wai Leung and Chi-Keung Ng and Ngai-Ching Wong},
  journal= {arXiv preprint arXiv:1005.4561},
  year   = {2010}
}
R2 v1 2026-06-21T15:27:29.726Z