In quantum physics, the mathematical notion is usually applied to representations of the gauge group. For example, an SU ( 2 ) gauge theory will have multiplets which are fields whose representation of SU ( 2 ) is determined by the single half-integer number s =: n / 2 , the isospin. Since irreducible SU ( 2 ) representations are isomorphic to the n th symmetric power of the fundamental representation, every field has n symmetrized internal indices.