All Questions
Tagged with quantum-chromodynamics standard-model
26
questions with no upvoted or accepted answers
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
8
votes
0
answers
183
views
Question about the vacua of the Standard Model
This question is probably based on a misunderstanding. Please correct me if I'm wrong, and if unclear, I'll try to put it in a clearer language.
In Yang-Mills theory such as the theory of strong ...
- 26.8k
6
votes
0
answers
239
views
From $U(3)$ to $SU(3)\times U(1)$ Color symmetry. There is a "gluon" photon-like?
Suppose that $U(3)$ was the gauge group. We can decompose this as
$U(3)=U(1)\times SU(3)$,
which implies that in addition to the $SU(3)$ that has eight generators corresponding to eight gluons, there ...
- 558
5
votes
0
answers
347
views
How Is Are Parton Distribution Functions (PDFs) Determined In Practice And In Theory?
I have put my actual questions in bold normal font, and the rest of this question clarifies what I mean to be asking, especially in terms of the depth and kinds of information I am looking for. ...
- 3,957
3
votes
0
answers
67
views
When do pairs of quarks form jets vs mesons?
For certain processes with low momentum transfer, such as the Kaon decay shown below, quarks will form bound states of mesons.
Whereas for higher momentum-transfer processes, such as the decay of an ...
3
votes
0
answers
294
views
What's the meaning of QCD phase transition temperature?
I read about the QCD energy level in various sources, eg: Wikipedia, and this gives a phase transition temperature of about 200 MeV, above which quark confinement breaks down and we may observe ...
2
votes
0
answers
84
views
How many extra dimensions needed to model the Strong interaction with a Kaluza-Klein extended theory?
The blog / video (See: https://backreaction.blogspot.com/2021/04/does-universe-have-higher-dimensions.html - Does the Universe have Higher Dimensions? Sabine Hossenfelder's blog) is discussing the ...
- 61
2
votes
0
answers
94
views
Is there any progress in the study of the relationship between Rubik's cube and quark?
After Golomb discovered the relationship between Rubik's cube and quark, Anthony E. Durham improved it. Is there a link to Anthony E. Durham's work? May be the principal bundles can explain the ...
2
votes
0
answers
368
views
Simplify QCD Lagrangian
How we can derive the electric charge of the field theory for each field?
For example lets say that we have the u-quarks (3-colors) and electron that we know that has charge -e) free Lagrangian
$$\...
- 145
1
vote
0
answers
35
views
Evidence of more generations in the QCD beta function
We know that the beta function for QCD is
$$
\beta = -\left(11 - \dfrac{2N_f}{3}\right),
$$
where $N_f$ is the number of fermions in the theory. We have $\beta_{\text{SM}} = -7$.
Now, my question is, ...
- 1,611
1
vote
0
answers
106
views
Do quarks have a non-zero electric dipole moment?
It is written here, in this PSE link that an electron has a measured perfect spherical charge density therefore a zero electric dipole moment (i.e. perfect monopole charge).
My question is, are quarks ...
- 4,170
1
vote
0
answers
63
views
Can the process gluon + gluon $\rightarrow$ 2 Higgs proceed in the following way in the standard model?
At order $g_s^2$, usually only a triangle quark loop and box diagram are considered, I was wondering, is there some reason that excludes these diagrams from the possible standard model channels?
1
vote
2
answers
30
views
Understanding Jet Clustering: Why is only $p_{T}$ used?
Let's only consider iterative jet clustering algorithms. Famous ones are the $k_{T}$ ($p = 1$), anti-$k_{T}$ ($p = -1$) and Cambridge/Aachen ($p = 0$) jet reconstruction algorithms.
All these ...
user248824
1
vote
0
answers
51
views
What are extrinsic and intrinsic flavour production?
In terms of Feynman diagrams, what are extrinsic and intrinsic flavour production?
See for example this paper this paper (p.2).
- 1,187
1
vote
0
answers
69
views
Regge theory and $SU(3)$ mass formula
In a video interview, Murray Gell-Mann states (at 40 seconds)
"I have wondered all this time, and I still wonder, whether the straightness of those [Regge] trajectories, and the accuracy of the ...
- 13.1k