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Improvement of the Calculation of Scattering Amplitudes with External Fermions

E. Chopin
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Abstract

In this paper, we present an improvement of a method for computing scattering amplitudes that include external (polarized) fermions with the following features: the formulas are quite general and work for different kinematic configurations and different external masses, they are explicitly covariant, they do not depend on a specific representation of the Dirac matrices and they have a meaningful limit when the masses tend to 0. The results presented make use of some well known formulas describing the density matrices in terms of projection operators within a more general formalism. Since our formulas intend to be as general as possible, we also take into account the possibility of a transverse polarization for massless fermions.

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E. Chopin. 1998-06-17. Improvement of the Calculation of Scattering Amplitudes with External Fermions. https://arxiv.org/abs/hep-ph/9805203

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