All Questions
Tagged with quantum-chromodynamics gauge-theory
77
questions
2
votes
1
answer
1k
views
The logic of large $N$ expansion
I have some understanding of how the large-$N$ expansion works but feel like I'm missing the most important concepts.
For example, I understand that in QCD the order of the diagram in $N$ depends ...
- 2,921
11
votes
0
answers
445
views
Is the QCD Lagrangian without a $\theta$-term invariant under large gauge transformations?
In his book "Quantum field theory", Kerson Huang states that we need to add the term $$\frac{i\theta}{32\pi^2}G_{\mu\nu}^a \tilde{G}_{\mu\nu}^a$$ to the Lagrangian, to make it invariant under large ...
- 10.1k
3
votes
1
answer
270
views
How many glueballs are there?
As I understand there are eight types of gluons (linear combinations of color/anticolor pairs with varying amplitudes) which can combine (for very short periods) to form glueballs. If there were no ...
- 756
1
vote
1
answer
176
views
Why group elements associated with gauge transformations of finite action field configurations in QCD don't depend in $r$?
I am reading the chapter on instantons in Coleman's Aspects of Symmetry. I am puzzled by an argument i don't quite follow. In section 3.2, Coleman considers configurations of the gauge field with ...
- 6,067
11
votes
1
answer
3k
views
Polarization Sums in QCD for the calculation of parton model splitting functions
Before i state the actual problem, here's a premise. In the case of a Spin 1 massive particle it's possible to demonstrate that $$\sum_{\lambda=0,\pm1}\epsilon_{\lambda}^{* \ \mu}\epsilon_{\lambda}^{\...
- 2,263
7
votes
2
answers
421
views
Is there some no-go theorem for $D=9$ Kaluza Klein QCD+EM?
While QCD is a typical product of AdS/CFT and some other research trends in extra dimensions, I have never found in the literature an example producing the non-chiral part of the standard model, ...
- 1,943
7
votes
1
answer
479
views
Massive Gauge Bosons without Higgs fields
In a possible theory like our Standard model but without a Higgs i.e.:
$$ \mathcal{L}=i\bar{\Psi}_f\gamma_\mu D^\mu\Psi_f-\text{Tr}[G^b_{\mu\nu}G^{b\,\mu\nu}] $$
where $b,f$ run over the typical ...
- 823
12
votes
1
answer
397
views
Why does strong interaction increase with distance?
I read numerous times that strong interaction increases with distance. But how can one actually derive the force-distance relation from the lagrangian (quark field + gluon field + gauge coupling)? ...
- 644
10
votes
1
answer
708
views
Does the LSZ reduction method prove gauge-independence in massless gauge theories?
I've been working my way through L. Baulieu's excellent paper [Perturbative gauge theories,
Physics Reports, Volume 129, Issue 1, December 1985, Pages 1-74]. Towards the end, he goes on to prove that ...
- 101
22
votes
1
answer
7k
views
How to Perform Wick Rotation in the Lagrangian of a Gauge Theory (like QCD)?
I'm studying Lattice QCD and got stuck in understanding the process of going from a Minkowski space-time to an Euclidean space-time. My procedure is the following:
I considered the Wick rotation in ...
- 532
12
votes
3
answers
4k
views
Why is color conserved in QCD?
According to Noether's theorem, global invariance under $SU(N)$ leads to $N^2-1$ conserved charges. But in QCD gluons are not conserved; color is. There are N colors, not $N^2-1$ colors. Am I ...
- 7,398
7
votes
1
answer
1k
views
Weak isospin and types of weak charge
My understanding is that QCD has three color charges that are conserved as a result of global SU(3) invariance. What about SU(2) weak? Does it have two types of charges? What I'm getting at is:
U(1) -...
- 7,398
2
votes
2
answers
411
views
In a gauge theory, are two states related by a global phase transformation identified?
In a gauge theory (non-abelian for this question), I am told that two states $|\psi\rangle$ and $|\phi\rangle$ are to be identified if they are related by a gauge transformation $U(x)$
$$|\psi\rangle\...
- 6,381
7
votes
1
answer
2k
views
Wilson loops and gauge invariant operators (Part 2)
These questions are sort of a continuation of this previous question.
I would like to know of the proof/reference to the fact that in a pure gauge theory Wilson loops are all the possible gauge ...
- 4,561
12
votes
4
answers
4k
views
What's the distinctions between Yang-Mills theory and QCD?
So Yang-Mills theory is a non-abelian gauge theory, and we used a lot in QCD calculation.
But what are the distinctions between Yang-Mills theory and QCD?
And distinctions between supersymmetric ...
- 393