TENSOR PRODUCT OF GROUP-REPRESENTATIONS AND STRUCTURAL ZEROS OF RACAH COEFFICIENTS

It is shown that structural (or nontrivial) zeros of Racah coefficients (6-j symbols) can be related to decompositions of tensor products of group representations reduced to SO(3). This extends a previous relation between structural zeros of 6-j symbols and boson realizations of exceptional Lie groups. In the present case, both classical and exceptional groups may appear, and examples are given for SU(3), SO(7), SO(9), and F4.