C∗-algebras Generated by a Subnormal Operator
نویسنده
چکیده
Using the functional calculus for a normal operator, we provide a result for generalized Toeplitz operators, analogous to the theorem of Axler and Shields on harmonic extensions of the disc algebra. Besides that result, we prove that if T is an injective subnormal weighted shift, then any two nontrivial subspaces invariant under T cannot be orthogonal to each other. Then we show that the C∗-algebra generated by T and the identity operator contains all the compact operators as its commutator ideal, and we give a characterization of that C∗-algebra in terms of generalized Toeplitz operators. Motivated by these results, we further obtain their several-variable analogues, which generalize and unify Coburn’s theorems for the Hardy space and the Bergman space of the unit ball.
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