Abstract. In this paper we introduce simple multipliers, a special subclass of multipliers on a Banach module. We show that, from a local spectral point of view, these multipliers behave like multipliers on a commutative Banach algebra. Our definition of simple multipliers relies on the notion of point multipliers. These multipliers were studied earlier. However our approach gives new insight into this topic and therefore could be of some interest by itself.2000 Mathematics Subject Classification. Primary 46H25; Secondary 47B40. The goal of the present paper is to discuss the decomposability of multipliers between Banach modules. Since, for a general multiplier, we cannot say very muchfor instance, if A = ,ރ then B A (X) = B(X) -it is quite clear that we have to confine ourselves to a special subclass of multipliers. In Section 4 we introduce simple multipliers on a Banach left module, which seem to be the suitable environment for our questions. Section 5 is devoted to the local spectral theory of simple multipliers. For instance, we extend to the class of simple multipliers on a left Banach module some results that are proven in [8], [16] and [23] only for algebras. Our definition of simple multipliers relies on the notion of point multipliers, which are studied in Sections 2 and 3. We believe that the content of these two sections are of some interest by itself.
Introduction. A mapping T on a Banach algebraIt is assumed that the reader is familiar with the concept of Banach modules. We refer to [1, 18, 24], for details.