Euclidean signature and compact gauge group

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Discussion Overview

The discussion revolves around the analytic continuation to Euclidean space in the context of gauge fields and the implications for maintaining a compact gauge group. Participants explore the relationship between the continuation of gauge fields and the properties of gauge transformations, particularly in the transition from Minkowski to Euclidean space.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes the necessity of continuing the gauge field when transitioning to Euclidean space to maintain the compactness of the gauge group.
  • Another participant suggests that this requirement is related to keeping the representation of the gauge transformation unitary and finite dimensional.
  • A request for sources or methods to demonstrate this relationship is made, indicating a desire for further clarification or evidence.
  • It is mentioned that transitioning from Minkowski space to Euclidean space involves substituting the proper orthochronous Lorentz group with O(4), which affects the nature of four-vectors and the gauge group.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and seek clarification on specific aspects, indicating that the discussion remains unresolved with multiple viewpoints on the implications of the analytic continuation.

Contextual Notes

There are references to specific texts and authors that may address the topic, but no consensus on a definitive source or explanation is reached. The discussion highlights the complexity of the relationship between gauge fields and their transformations in different spacetime signatures.

Who May Find This Useful

This discussion may be of interest to graduate students and researchers in theoretical physics, particularly those studying quantum field theory and gauge theories.

Einj
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Hello everyone,
I have been reading around that when performing the analytic continuation to Euclidean space (t\to-i\tau) one also has to continue the gauge field (A_t\to iA_4) in order to keep the gauge group compact.
I already knew that the gauge field had to be continued as well but I didn't know anything about keeping the gauge group compact. Can someone explain it to me?

Thanks!
 
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I believe it has to do with keeping the representation of the gauge transformation unitary and finite dimensional.
 
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Do you have any idea on how to show it or any source I could look at? Thanks for you reply!
 
I would guess any decent grad text on field theory might cover this. I don't know of one myself. I recall reading something on the complexification in Ryder's book "Quantum Field Theory" but I don't recall him speaking of justification. I don't recall Kaku addressing it directly in his book but I haven't peeked in his text in a while and didn't read it extensively when I last did. Maybe someone else has a suggestion?
 
The point is that you entirely go from Minkowski space with a fundamental form of signature (1,3) (or (3,1) if you come from the east coast ;-)) to Euclidean space, i.e., the proper orthochronous Lorentz group is substituted by O(4). So all four-vectors become Euclidean vectors. The gauge group stays as it is, i.e., a compact Lie group.
 
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Oh I see! Thanks a lot
 

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