We focus mainly on the scattering between two particles of four-momenta\(p_1\) and\(p_2\) going into a final state of two other particles of four-momenta\(p_3\) and\(p_4\). The types of particles in the final and initial states might be different.

1. 1.

   For a general Lorentz transformation these manipulations give rise to the Wigner rotation [5].

2. 2.

   The Clebsch–Gordan coefficient\((m_1 m_2 m_3|j_1j_2j_3)\) is the composition for\(\mathbf {j}_1+\mathbf {j}_2=\mathbf {j}_3\), with\(m_i\) referring to the third components of the spins.

3. 3.

   They correspond to those indicated under the summation symbol in Eq. (2.30) both for the initial and final states.

4. 4.

   The potential is also required to fulfill this property,\(v(z)^\dagger =v(z^*)\).

Authors and Affiliations

1. Departamento de Física, Universidad de Murcia, Murcia, Spain

   José Antonio Oller

Corresponding author

Correspondence toJosé Antonio Oller.

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