On C*-Extreme Maps and *-Homomorphisms of a Commutative C*-Algebra

TL;DR

This paper characterizes C*-extreme points of the generalized state space of a commutative C*-algebra, showing they satisfy spectral conditions and are multiplicative when mapping into certain operator algebras, thus generalizing previous results.

Contribution

It establishes spectral conditions for C*-extreme maps and proves their multiplicativity into the algebra generated by compact and scalar operators, extending prior work.

Findings

C*-extreme points satisfy specific spectral conditions

C*-extreme maps into K^+ are multiplicative

Structure of these maps is explicitly determined

Abstract

The generalized state space of a commutative C*-algebra, denoted S_H(C(X)), is the set of positive unital maps from C(X) to the algebra B(H) of bounded linear operators on a Hilbert space H. C*-convexity is one of several non-commutative analogs of convexity which have been discussed in this context. In this paper we show that a C*-extreme point of S_H(C(X)) satisfies a certain spectral condition on the operators in the range of the associated positive operator-valued measure. This result enables us to show that C*-extreme maps from C(X) into K^+, the algebra generated by the compact and scalar operators, are multiplicative. This generalizes a result of D. Farenick and P. Morenz. We then determine the structure of these maps.