Dirac algebra (contraction gamma matrices)

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SUMMARY

The discussion centers on the contraction of gamma matrices in Dirac algebra, specifically the expression \(\gamma^{\mu}_{ab}\gamma_{\mu \,\alpha\beta}\). Participants highlight the necessity of mixing dotted and undotted indices due to the first gamma matrix being sandwiched between two spinors. The Fierz identities are referenced as a crucial tool for expressing the product of two Dirac matrices in terms of matrices in the crossed channel, specifically transforming \((\gamma^{\mu})_{ab}(\gamma_{\mu})_{cd}\) into \((\gamma^{\mu})_{ad}(\gamma_{\mu})_{bc}\). A comprehensive resource on this topic is provided through a link to a detailed treatment of the Fierz transformations.

PREREQUISITES
  • Understanding of Dirac algebra and gamma matrices
  • Familiarity with spinor notation and indices
  • Knowledge of Fierz identities in quantum field theory
  • Basic principles of quantum mechanics and relativistic quantum fields
NEXT STEPS
  • Study the Fierz identities in detail, focusing on their applications in quantum field theory
  • Explore the properties of gamma matrices and their role in the Dirac equation
  • Learn about the implications of mixing dotted and undotted indices in spinor calculations
  • Investigate advanced topics in quantum field theory, such as perturbation theory and scattering amplitudes
USEFUL FOR

Physicists, particularly those specializing in quantum field theory, theoretical physicists working with Dirac algebra, and students seeking to deepen their understanding of gamma matrices and spinor interactions.

IRobot
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I would like to have a general formula, and I am quite sure it must exist, for: \gamma^{\mu}_{ab}\gamma_{\mu \,\alpha\beta} but I didn't succeed at deriving it, or intuiting it, I am troubled by the fact that it must mix dotted and undotted indices.
 
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Why does it have different type of indices ?
 
Because the first gamma matrix is sandwiched between two spinors.
 
IRobot, I think what you are referring to are the Fierz identities, which express the product of two Dirac matrices in terms of matrices in the crossed channel. That is, (γμ)abμ)cd expressed in terms of (γμ)adμ)bc. See http://gemma.ujf.cas.cz/~brauner/files/Fierz_transform.pdf for an exhaustive treatment!
 

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