Composition Operators on Some Semi-Hilbert Spaces

In this paper, we study composition and weighted composition operators on semi-Hilbert spaces induced by positive multiplication operators on \( L^۲(\mu) \). Within the framework of \( A \)-adjoint operators, we characterize the conditions under which a composition operator \( C_\varphi \) is \( A \)-selfadjoint, \( A \)-normal, \( A \)-quasinormal, or \( A \)-unitary, where \( A = M_u \) denotes a positive multiplication operator. In addition, we provide necessary and sufficient conditions for \( C_\varphi \) to be an \( A \)-isometry or an \( A \)-partial isometry. Analogous results are also obtained when \( A \) is a positive composition operator. Several examples are included to illustrate the applicability of the main results.

کلیدواژه ها:

composition operator ، Semi-Hilbert space ، Multiplication operator