Positivity conditions on the spin density matrix: A simple parametrization

@article{Chung1975PositivityCO,
  title={Positivity conditions on the spin density matrix: A simple parametrization},
  author={S. U. Chung and T. Laurence Trueman},
  journal={Physical Review D},
  year={1975},
  volume={11},
  pages={633-646}
}
A simple parametrization of the spin density matrix $\ensuremath{\rho}$ is given which ensures that $\ensuremath{\rho}$ is a positive, Hermitian matrix which satisfies the parity symmetry conditions. There is a minimal number of parameters and they can vary independently; no complicated constraints on their allowed region of variation are required. A similar parametrization is given for the real part of $\ensuremath{\rho}$. Rank conditions, polarized targets, and angular distributions are also… 
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