Open Diagrams

Abstract

Simple examples of open diagrams with external lines have been encountered in our discussion of orthogonality relations for 3jm-symbols. One might say that, open diagrams are more general than closed diagrams of the preceding section. Furthermore, open diagrams will be nearer to the calculation of matrix elements of spherical tensor operators, which contain a 3jm-symbol according to the Wigner–Eckart Theorem, and a reduced matrix element with one or more 3nj-symbols. In the end, a realistic calculation can involve products of open and closed diagrams and in Chap. 10 an example is analysed. From Chap. 7, on general rules, we recall that separations are possible if all the external lines stay with one of the separated parts.