Classification of quasi-homogeneous holomorphic curves and operators in the Cowen–Douglas class☆

Abstract In this paper we study quasi-homogeneous operators, which include the homogeneous operators, in the Cowen–Douglas class. We give two separate theorems describing canonical models (with respect to equivalence under unitary and invertible operators, respectively) for these operators using techniques from complex geometry. This considerably extends the similarity and unitary classification of homogeneous operators in the Cowen–Douglas class obtained recently by the last author and A. Koranyi. In a significant generalization of the properties of the homogeneous operators, we show that quasi-homogeneous operators are irreducible and determine which of them are strongly irreducible. Applications include the equality of the topological and algebraic K -group of a quasi-homogeneous operator and an affirmative answer to a well-known question of Halmos.