Are there separate quantum fields for spin 1/2 particles in modern QFT?

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Discussion Overview

The discussion centers on the nature of quantum fields for spin 1/2 particles within modern quantum field theory (QFT). Participants explore the relationship between the spin observable, represented by Pauli Matrices, and the implications for the existence of separate quantum fields for these particles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the spin observable for spin 1/2 particles is represented by Pauli Matrices in a 2-dimensional Hilbert Space and questions whether this "TWO-ness" translates to modern QFT with separate quantum fields.
  • Another participant affirms that the Dirac Equation is applicable in relativistic quantum field theory.
  • A third participant raises concerns about the separation of angular momentum into orbital and spin components, suggesting that this is problematic in relativistic QFT and referencing Wigner's analysis of irreducible unitary representations of the Poincare group.
  • Additionally, a participant mentions that the Dirac equation can be viewed as a single fourth-order differential equation for one function, providing links to their own article and further derivations.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the Dirac Equation and the nature of spin in QFT, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

There are unresolved questions regarding the interpretation of spin in the context of relativistic QFT and the implications of the Dirac Equation, as well as the potential limitations of separating angular momentum components.

LarryS
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The spin observable for spin 1/2 particles is represented by Pauli Matrices acting upon a 2-dimensional Hilbert Space. In RQM, forgetting about the matter-antimatter duality for the moment, that TWO-state Hilbert Space is directly related, through the Lorentz Group, to the TWO separate differential equations in the Dirac Equation. Is that same "TWO-ness" also found in modern QFT for spin 1/2 particles? Are there TWO separate quantum fields for a spin 1/2 particle in modern QFT? As always, thanks in advance.
 
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The Dirac Equation holds in relativistic quantum field theory.
 
In addition one cannot stress early enough that a split of angular momentum in an orbital and a spin part is problematic in relativistic quantum field theory (to say the least). A thorough understanding of what's "spin" in relativistic QFT necessarily leads to Wigner's analysis of the irreducible unitary representations of the (quantum version of the) Poincare group. See

Weinberg, S.: The Quantum Theory of Fields, volume 1, Cambridge University Press, 1995

or my QFT lecture notes:

http://fias.uni-frankfurt.de/~hees/publ/lect.pdf
 
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