Separation conjecture for Hilbert C*-submodules by bounded modular functionals

Let AA be a C*-algebra, and let M\mathcal M be a Hilbert AA-submodule of a Hilbert AA-module N\mathcal N. Suppose that the orthogonal complement of M\mathcal M relative to N\mathcal N is trivial:

M={0}.\mathcal M^\perp=\{0\}.

Separation conjecture. There does not exist any non-trivial bounded AA-linear map from N\mathcal N to AA that is equal to the zero map on M\mathcal M.

This is equivalent to asking whether adequate bounded modular functionals always separate Hilbert C*-submodules, or equivalently whether non-trivial extensions of the zero modular functional exist. It is also related to the existence of non-regular bounded modular operators on the hosting Hilbert C*-module; the supplied text does not state whether the conjecture is resolved.

Sources & referencesView supporting material

Primary source

Michael Frank and Cristian Ivanescu, “Bounded modular functionals and operators on Hilbert C*-modules that are regular”, arXiv:2603.24042 (2026).

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