Summability of sequences and extensions of operator ideals

Abstract

Given a Banach space Y , the so-called right Y and left Y -extensions of operator ideals are introduced and applied to the study of operator ideal properties of well-known classes of operators on Banach spaces. The key is to introduce a general theory (in the context of operator ideal theory) to study some classes of operators which are right or left Y -extensions of classical operator ideals for some Banach space Y . This leads to a study of a class of operators, called (r; Y_q)- limited operators, which generalises some recently introduced operators in the literature. In particular, the results of this study are applied to obtain characterisations and new information about the sequentially p-limited operators, weakly mid (q; p; r)-summing operators, p-convergent (or p-converging) operators and weak^* p-convergent operators.