Neutrinoless double beta decay matrix elements beyond closure approximation

Abstract

The nuclear matrix elements of all operators entering 0ν ββ-decay beyond closure approximation have been calculated in the case of A = 48. Within the 0 f 7 2 model we find that the closure approximation is quite good. The various intermediate states contribute additively. The retardation of the usual matrix elements can be traced to the reduced matrix elements connecting the intermediate states to the final. The matrix elements associated with heavy neutrinos and the recoil term are not retarded.