Abstract:

In the theory of Hilbert $C^*$-modules over a $C^*$-algebra $\mathcal A$ (in contrast with the theory of Hilbert spaces) not each bounded operator ($\mathcal A$-homomorphism) admits an adjoint. The interplay between the sets of adjointable and non-adjointable operators plays a very important role in the theory. We study an intermediate notion of locally adjointable operator $F:\mathcal M \to \mathcal N$, i.e. such an operator that $F\circ \gamma$ is adjointable for any adjointable $\gamma:\mathcal A \to \mathcal M$. We have introduced this notion recently and it has demonstrated its usefulness in the context of theory of uniform structures on Hilbert $C^*$-modules. In the present paper we obtain an explicit description of locally adjointable operators in important cases.