Factorization in the invertible group of a $C^*$-algebra

http://dx.doi.org/10.4153/CJM-1997-058-7
Canad. J. Math. 49(1997), 1188-1205

  Published:1997-12-01
 Printed: Dec 1997

In this paper we consider the following problem: Given a unital \cs\ $A$ and a collection of elements $S$ in the identity component of the invertible group of $A$, denoted \ino, characterize the group of finite products of elements of $S$. The particular $C^*$-algebras studied in this paper are either unital purely infinite simple or of the form \tenp, where $A$ is any \cs\ and $K$ is the compact operators on an infinite dimensional separable Hilbert space. The types of elements used in the factorizations are unipotents ($1+$ nilpotent), positive invertibles and symmetries ($s^2=1$). First we determine the groups of finite products for each collection of elements in \tenp. Then we give upper bounds on the number of factors needed in these cases. The main result, which uses results for \tenp, is that for $A$ unital purely infinite and simple, \ino\ is generated by each of these collections of elements.