All Questions
Tagged with quantum-chromodynamics yang-mills
93
questions
7
votes
1
answer
442
views
Is Yang-Mills theory confining in any dimensions?
What is the current understanding of Yang-Mills theory (pure non-Abelian gauge theory without matter field) in the infrared limit? (To avoid the subtlety of renormalizability, we may restrict our ...
- 11.9k
1
vote
0
answers
61
views
Could we draw field lines for colour charge?
Electromagnetic charge can be represented with field lines. These are pleasingly intuitive and can be used to visualise Gauss's Law and Maxwell's Laws. Later on Gauss and Maxwell get rolled into a ...
- 183
3
votes
0
answers
376
views
Mass gap v.s. classical nonlinear Yang-Mills waves
Why people said (Witten, p. 11),
"For Yang-Mills theory. the mass gap is the reason that we do not see classical nonlinear Yang-Mills waves. They are a good approximation only under inaccessible ...
- 4,336
7
votes
1
answer
306
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Non-abelian string in QCD?
It is easy to find various/many papers in HEP-lattice talk about "Non abelian string in QCD".
What does it mean to say "non abelian string in QCD?" Does "non abelian string" happen for pure Yang-...
- 4,336
6
votes
1
answer
778
views
A question on large-N limit?
Let's take $SU(N)$ for an example. The Lagrangian is
$$\mathcal{L}=-\frac{1}{4g_{YM}^2}F_{\mu\nu}F^{\mu\nu}.$$
We can define the t'Hooft coupling as
$$\lambda=g_{YM}^2N.$$
Then the large-$N$ limit ...
- 3,691
7
votes
1
answer
2k
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Why is the temporal gauge $A_0=0$ so popular in discussions of non-perturbative effects?
Almost every discussion of non-perturbative effects in Yang-Mills theory mentions in passing that they work in the temporal gauge. Why is this the case?
A good example is the QCD vacuum. Almost ...
- 10.1k
1
vote
0
answers
40
views
2D QCD Phase Transitions of Free Energy Gross & Taylor [closed]
Hi I'm currently working on the paper "Counting Strings and Phase Transitions in 2D QCD" by W. Taylor, for the most part the paper is quite easy to understand however I cannot see how he manages to ...
- 11
10
votes
1
answer
888
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Why is is the vacuum expectation value (VEV) of the axion field such that it cancels the theta angle of QCD?
Why does the vacuum expectation value of the axion field $a(x)$ take on the value $\langle a \rangle = -\theta f_a/\xi \sim -\theta$, i.e. the vacuum theta angle of QCD? (Sources or proof if possible.)...
- 101
6
votes
2
answers
2k
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double line notation (three and four gluon vertices) - how is this a simplification?
This is closely related to my previous post Double line notation - gluon propagator
I'm trying to understand the double-line vertices for the gluon in the case of a $U(N)$ gauge group. Normally, the ...
- 3,719
5
votes
1
answer
262
views
Would the existence of more than 16 quark flavors make QCD deconfinning?
Consider the QCD beta function. Its expansion in powers of the coupling is
$$\beta(\mu)=-(\beta_0a(\mu)+\beta_1a^2(\mu)+\ldots)$$
where $a=\alpha/4\pi$. For simplicity let's neglect everything but ...
- 6,067
5
votes
2
answers
927
views
Yang-Mills theories, confinement and chiral symmetry breaking
I was thinking about hadrons in general Yang-Mills theories and I have some doubts that I'd like to discuss with you.
Suppose that we have a Yang-Mills theory that, like QCD, tend to bind quarks ...
- 300
5
votes
0
answers
428
views
Unitarity of the S-matrix and Feynman Diagrams
There are several questions on the unitarity of the S matrix, but unfortunately non of them answers directly the following question.
The S matrix is unitary and that can be proven by the fact that ...
- 1,210
0
votes
1
answer
1k
views
Completeness Relations of Polarization Vectors in QCD
What are the completeness relations of the polarization vectors of (external) particles in QCD amplitude calculation?
(I assume the polarization vectors depend on the gauge and even so still have some ...
- 3,369
4
votes
0
answers
322
views
Why is QCD hard to solve if I know the beta functions?
Why is it still hard to solve QCD if we know the beta functions of the coupling? Aren't only the loops causing problems? And am I not able to write every possible interaction exact at tree-level with ...
- 2,147
1
vote
1
answer
474
views
How to compute this loop integral? [closed]
I have a gauge boson that splits into two scalars and the loop is closed by a gauge boson as shown in the picture. The incoming boson has $\mu$ index while the boson that runs in the loop has momentum ...
- 2,188