Normal extensions escape from the class of weighted shifts on directed trees

Zenon Jan Jablonski, Il Bong Jung, Jan Stochel

Published 2011-04-22Version 1

A formally normal weighted shift on a directed tree is shown to be a bounded normal operator. The question of whether a normal extension of a subnormal weighted shift on a directed tree can be modeled as a weighted shift on some, possible different, directed tree is answered.