Branching rules for the subgroups of the unitary group
D. Braunschweig, K. T. Hecht · Journal of Mathematical Physics · 1978
Expressions are given in terms of simple matrices d for the reduction of the Kronecker (outer) product of two or more irreducible representations which can be characterized by Young patterns. These are then used to obtain practical formulas for branching rules. The needed matrices d can be constructed by a very efficient recursive process.