All Questions
Tagged with quantum-chromodynamics gauge-theory
77
questions
1
vote
2
answers
424
views
Why does QCD become strongly interacting at low energies and how low is low here?
A few days ago I asked a question about QCD chiral symmetry breaking and hopefully got a very good answer. But the problem is I am not well-versed in QCD to fully appreciate the answer there. I know ...
- 11.8k
2
votes
2
answers
573
views
Understanding the prefactor $\frac{\theta g^2}{32\pi^2}$ of the $F\tilde{F}$ term in Yang-Mills theories
The most general Yang-Mills (YM) action consistent with Lorentz invariance, gauge invariance and renormalizability should contain a term $$\kappa F_{\mu\nu a}\tilde{F}^{\mu\nu a}\tag{1}$$ where $\...
- 26.8k
1
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2
answers
746
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How does the underlying symmetry of QCD imply the allowance of a 4-gluon vertex?
Quantum chromodynamics allows for a four-gluon vertex such as this, in a diagram
Such a vertex would never be allowed in quantum electrodynamics, which has an underlying U(1) gauge symmetry.
I know ...
- 324
3
votes
0
answers
324
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A Question about Wave-Function Renormalization Factor in SQCD
Here, I have a question about the one-loop computation of the wave-function renormalization factor in SQCD.
According to Seiberg duality, the following electric $\mathrm{SQCD}_{e}$
\begin{gather}
...
- 2,923
2
votes
0
answers
72
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What happens to large gauge transformations in gauges different from the temporal gauge?
There are already several questions regarding the meaning and definition of large gauge transformations.
Discussions of large gauge transformations typically only happen in the context of the ...
- 10.1k
2
votes
1
answer
529
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$U(N)$ & $SU(N)$ : What's the conceptual difference in Gauge Theory?
I know the mathematical difference that one means $ absolutevalue(det) = 1$ and one means det = 1 (rotation) and that ones the subgroup of the other and so on.
But:
has a local/gauged $SU(3)$ ...
- 91
6
votes
0
answers
386
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A Naive Question about Gauge Theory
I am suffering from a question I encountered from the lecture notes of gauge theory by David Tong. The problem comes from page 67 on the gauge fixing in back-ground gauge method. In David Tong's ...
- 2,923
4
votes
1
answer
2k
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Why quarks in the fundamental and gluons in the adjoint?
I have been told that in gauge theories
“fermionic matter goes in the fundamental rep of $SU(N)$, while gauge fields go in the adjoint rep”.
I understand how this works, and for instance, in QCD,...
- 1,154
0
votes
0
answers
562
views
Wilson loop and Polyakov loop
As I understand, the Wilson line is the operator $W(x) = P\exp(i\int_{xi}^{xf} A.dx)$, where $P$ is path ordering. The Polyakov loop $P(x)$ on the other hand is the trace of the Wilson loop $W(x)$ ...
- 1,023
0
votes
0
answers
203
views
QCD vs. QED gauge invariance
Trying to understand the difference between QED and QCD gauge invariance treatment I found the following paper: https://arxiv.org/abs/1101.3425
I have the following questions:
I understand Eq. (42) ...
- 1,597
3
votes
2
answers
974
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Invariance of Yang-Mills Lagrangian under charge conjugation
The Yang-Mills Lagrangian gauge invariant under an $SU(N)$ tranformation can be written as
$${\cal L} = -\frac{1}{4}F_{\mu\nu}^i F^{i\ \mu\nu} \tag1$$
(Sum over $i$ implicit)
This Lagrangian ...
- 1,597
4
votes
1
answer
528
views
Is color charge quantized?
I was reading this stackexchange question, and found the answer to my question not totally answered. Clearly there is color and anti-color in analogy to electric charge, and color charge clearly ...
- 1,117
4
votes
0
answers
143
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What is the relation between the Gribov problem and color confinement?
I have heard that the Gribov problem is in some way related to color confinement (For instance: Gribov copies and confinement). Although I understand what both the Gribov and confinement problems are, ...
- 17.8k
3
votes
1
answer
267
views
Isn't there a unique vacuum of the Yang-Mills quantum theory?
The theta vacua$^1$ of a Yang-Mills quantum theory are given by $$|\theta\rangle=\sum\limits_{n=-\infty}^{\infty}e^{in\theta}|n\rangle.$$ In Srednicki's Quantum Field Theory, he claims that the ...
- 26.8k
6
votes
1
answer
2k
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What is the Noether charge associated with the the color $SU(3)$ symmetry of QCD?
A version of the Noether's theorem applies to local gauge symmetries. What is the Noether's charge associated with a non-abelian gauge symmetry such as the color $SU(3)$ and how is that derived? I ...
- 26.8k