General Relativity as a non-Abelian gauge theory

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Discussion Overview

The discussion explores the concept of general relativity (GR) being framed as a non-Abelian gauge theory, similar to quantum chromodynamics (QCD) and electroweak theory. Participants examine the technical feasibility of this approach and its implications within the context of differential geometry.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes the absence of a developed framework for GR as a gauge theory akin to QCD/electroweak theories and inquires about potential technical obstacles.
  • Another participant suggests that GR has influenced the development of Yang-Mills theories and discusses the introduction of an orthonormal frame to connect frame indices to tangent indices, proposing that the Riemann tensor acts as a Lie-algebra valued 2-form.
  • A later reply asserts that the analogy between GR and gauge theories is valid, particularly in the Palatini formalism, but highlights that the Riemann tensor involves second derivatives of the metric, contrasting with the first derivatives typically seen in the fibre bundle perspective.

Areas of Agreement / Disagreement

Participants express differing views on the technical aspects and implications of framing GR as a gauge theory, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

The discussion touches on the complexity of the principal bundle formalism and the mathematical intricacies involved, suggesting that a deeper understanding of differential geometry is necessary to fully engage with the topic.

masudr
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It occurred to me that I hadn't seen GR developed as a gauge theory in the same way QCD/electroweak are.

Are there any technical obstacles, or is it reasonably straightforward? And if it is well known, can someone please point me to a reference? Thanks.
 
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I think GR was actually one of the motivations behind Yang-Mills theories. I could wax poetically for hours about the subject, but any good "geometry for physicists" book will cover it. Basically you introduce an orthonormal frame which connects frame indices to tangent indices, and gauge those indices. So, for instance, your "field strength" is a Lie-algebra valued 2-form, namely the Riemann tensor. The method goes under the "principal bundle" formalism and can get quite heavy. But it is really simple, mathematicians just like to mathemagicate it.

The book by Nakahara is good, the book by Nash and Sen is good but contains a lot of typos. Anyway, it is more a thing about differential geometry than about GR. Ask if you need more.
 
I'll have a look at both. Thanks.
 
It works perfectly fine, especially in the Palatini formalism.

The main issue with the analogy is that the Riemann tensor contains second derivatives of the fundamental field 'entity' (the metric) whereas in the fibre bundle point of view, its really first derivatives
 

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