On the Relativistic Origin of Pseudo spin Symmetry in Nuclei

We review the concept of pseudo spin symmetry and its role in nuclear spectroscopy. We survey the attempts to arrive at a microscopic understanding of this symmetry. In particular, we show that pseudo spin symmetry in nuclei could arise from nucleons moving in a relativistic mean field which has an attractive scalar (Vs) and repulsive vector (Vv) potential nearly equal in magnitude but opposite in sign. We show that the generators of pseudo spin symmetry are the non-relativistic limit of the generators of an SU(2) symmetry which leaves invariant the Dirac Hamiltonian with Vs 2= -Vv. Furthermore within this framework, we demonstrate that this symmetry may be approximately conserved for realistic scalar and vector potentials