Yang-Mills, QED, QCD and Yukawa theories

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Discussion Overview

The discussion revolves around the differences between Yang-Mills theory, Quantum Electrodynamics (QED), Quantum Chromodynamics (QCD), and Yukawa theory, particularly focusing on their Lagrangians and the interactions they describe. It also touches on the historical context of Yukawa's work on meson-nucleon interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that Yang-Mills and QCD are based on non-abelian gauge symmetries, while QED is based on abelian gauge symmetry.
  • Others mention that Yukawa theory involves fermions and scalars, lacking spin-1 particles.
  • One participant questions the specific focus of Yukawa on meson-neutron interactions, prompting a clarification about the context of this focus.
  • Another participant corrects a typo regarding "nucleon" and emphasizes that the meson-nucleon interaction is central to Yukawa's theory, which predicts the existence of a meson that was unknown at the time.
  • It is suggested that the interaction Lagrangian in Yukawa theory is effective, applicable at energies lower than the QCD scale, due to the nature of the particles involved.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and interest in the differences between the theories, with some clarifying points and others posing questions. There is no consensus on the implications of these differences or the historical context of Yukawa's focus.

Contextual Notes

The discussion includes assumptions about the reader's familiarity with gauge theories and the specific interactions described by each theory. The nuances of the Lagrangians and their implications remain unresolved.

Who May Find This Useful

This discussion may be of interest to those studying theoretical physics, particularly in the areas of quantum field theory and particle physics.

Breo
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What is the difference between Yang-Mills and QED theories? Yukawa and QCD? specially in terms of the lagrangians.

I really want to get into this subject with a previously first sight.
 
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Breo said:
What is the difference between Yang-Mills and QED theories? Yukawa and QCD? specially in terms of the lagrangians.

I really want to get into this subject with a previously first sight.

Yang Mills and QCD ( which is just a particular Yang Mills theory) are based on non abelian gauge symmetries while QED is based on abelian gauge symmetry.

Yukawa theory doesn't have spin 1 particles, just fermions and scalars.

However, this is a very general question. I would recommend that you study the subject ( which would take some effort) and come back with more specific questions.
 
Why Yukawa focused on the search of the meson-neutron interaction?
 
Breo said:
Why Yukawa focused on the search of the meson-neutron interaction?

In what context? do you mean focused on meson-neutron and not meson-proton interactions?
 
Nucleon* typo
 
Breo said:
Nucleon* typo

In the Yukawa theory, the meson nucleon interaction is the pillar of theory. The nucleon-nucleon interaction is mediated by meson exchange, which is present due to the meson nucleon interaction.
The first and foremost prediction was that a meson with such properties exists, which was not known at the time the theory was published.
 
Why did he focus on the pion-nucleons? Because nucleons are fermions spin 1/2 particles while pions are scalar spin 0 particles.
Of course the interaction Lagrangian would be an effective one, since it corresponds to energies lower than the QCD scale...
 

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