On the closed convex hull of unitary orbits in certain C*-algebras. (2) Real rank zero for purely infinite corona algebras.
(1) Ando proved the following result:
Let A, B be self adjoint n by n matrices.
Then A is majorized by B if and only if A is an element of the convex hull
of the unitary orbit of B.
In this talk, we discuss infinite generalizations of the above result.
(2) Theorem: If B is a nonunital separable simple C*-algebra with strict comparison, almost divisibility,
stable rank one and quasicontinuous scale, then M(B)/B has real rank zero.
The above generalizes various results in the literature, with connections
to classical generalizations of the Weyl--von Neumann theorem as well as
attempts to generalize BDF Theory. The above
utilizes the following (earlier) result:
Theorem: Let B be a nonunital simple separable C*-algebra with strict
comparison, almost divisibility and stable rank one.
Then the following are equivalent:
(i.) B has quasicontinuous scale.
(ii.) M(B) has strict comparison.
(iii.) M(B)/B is purely infinite.
(iv.) M(B)/I_{min} is purely infinite.
(v.) M(B) has finitely many ideals.
(vi.) I_{min} = I_{fin}.