Subnormal Weighted Shifts on Directed Trees and Composition Operators in L 2-Spaces with Nondensely Defined Powers

الملخص EN

It is shown that for every positive integer n there exists a subnormal weighted shift on a directed tree (with or without root) whose nth power is densely defined while its ( n + 1 )th power is not.

As a consequence, for every positive integer n there exists a nonsymmetric subnormal composition operator C in an L 2-space over a σ-finite measure space such that Cn is densely defined and C n + 1 is not.