Derivations with values in an ideal $F$-spaces of measurable functions
A. A. Alimova,
V. I. Chilinb a Tashkent Islamic University,
11 Abdulla Kodiriy Ave., Tashkent, 100011, Uzbekistan
b National University of Uzbekistan,
Vuzgorodok, Tashkent, 100011, Uzbekistan
Abstract:
It is known that any derivation on a commutative von Neumann algebra
$ \mathcal {L}_{\infty} (\Omega, \mu)$ is identically equal to zero. At the same time, the commutative algebra
$\mathcal {L}_{0}(\Omega, \mu)$ of complex measurable functions defined on a non-atomic measure space
$(\Omega,\mu)$ admits non-zero derivations. Besides, every derivation on
$\mathcal{L}_{\infty}(\Omega, \mu)$ with the values in an ideal normed subspace
$X \subset \mathcal{L}_{0}(\Omega,\mu)$ is equal to zero. The same remains true for an ideal quasi-normed subspace
$X \subset\mathcal{L}_{0}(\Omega, \mu)$.
Naturally, there is the problem of describing the class of ideal
$F$-normed spaces
$X \subset \mathcal{L}_{0}(\Omega, \mu)$ for which there is a non-zero derivation on
$\mathcal{L}_{\infty}(\Omega, \mu)$ with the values in
$X $. We give necessary and sufficient conditions for a complete ideal
$F$-normed spaces
$X$ to be such that there is a non-zero derivation
$\delta: \mathcal{L}_{\infty}(\Omega, \mu) \to X$. In particular, it is shown that if the
$F$-norm on
$X$ is order semicontinuous, each derivation
$\delta: \mathcal{L}_{\infty}(\Omega, \mu) \to X$ is equal to zero. At the same time, existence of a non-atomic idempotent
$0\neq e \in X$,
$\mu(e) < \infty$ for which the measure topology in
$e \cdot X$ coincides with the topology generated by the
$F$-norm implies the existence of a non-zero derivation
$\delta: \mathcal{L}_{\infty}(\Omega, \mu)\to X$. Examples of such ideal
$F$-normed spaces are algebras
$\mathcal{L}_{0}(\Omega, \mu)$ with non-atomic measure spaces
$(\Omega, \mu)$ equipped with the
$F$-norm $\| f\|_{\Omega} = \int_{\Omega} \frac {| f |} {1+ | f |} d\mu $. For such ideal
$ F$-spaces there is at least a continuum of pairwise distinct non-zero derivations $\delta: \mathcal{L}_{\infty}(\Omega, \mu)\to (\mathcal{L}_{0}(\Omega, \mu), \|\cdot\|_{\Omega})$.
Key words:
derivation, an ideal space, $F$-norm.
UDC:
517.98 Received: 07.12.2017
DOI:
10.23671/VNC.2018.1.11393