The Recurrence Relation of Irreducible Tensor Operators for O(4)
  We derive the recurrence relation of irreducible tensor operator for O(4) in using the Wigner-Eckart theorem. The physical process like radiative transitions in atomic physics, nuclear transitions between excited nuclear states can be described by the matrix element of an irreducible tensor, which is expressible in terms of a sum of products of two factors, one is a symmetry-related geometric factor, the Clebsch-Gordan coefficients, and the other is a physical factor, the reduced matrix elements. The specific properties of the states enter the physical factor only. It is precisely this fact that makes the Wigner-Eckart theorem invaluable in physics. Often time one is interested in ratio of two transition matrix element where it is sufficient to regard only the Clebsch-Gordan coefficients. In this paper we first get the commutation relations of O(4), and then we choose one of these relations to operate on the certain eigenvectors. Finally we take summation over all possible eigenvectors and obtain rather the compact recurrence relation for irreducible tensor operators. 
Chin-Sheng Wu