All Questions
9
questions
6
votes
1
answer
857
views
Do gluons mediate the interactions between different flavors of quark?
From some of the quite professional sources (Basics from QCD by CERN; QCD from PDG), the QCD lagrangian is written in the form of
$$
L = \Sigma_{f} \; \bar{\psi}^{(f)} i \gamma^\mu D_\mu \psi^{(f)} + ...
- 165
2
votes
1
answer
169
views
Does pionium decay in massless QCD?
The bound state of ${\pi}^+ {\pi}^-$ is called Pionium.
Is Pionium an Electromagnetic bound state or a Strong Force one? then Why?
Does such a bound state last forever if one works in QCD with ...
- 1,268
14
votes
4
answers
2k
views
How does the strong force increase in attraction as particles move farther away?
I have heard that the strong force can be imagined similar to a rubber band, where the farther you extend the ends, the harder they pull themselves back together. My question is how? From what it ...
- 451
2
votes
2
answers
77
views
Error estimation of $\alpha_s$
I have calculated the strong coupling constant $\alpha_s$ using and approximate solution of the Renormalization Group Equation
$$\mu_R^2\frac{d\alpha_s}{d\mu_R^2}=-(b_0 \alpha_s^2 + b_1\alpha_s^3 + ...
- 21
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
5
votes
2
answers
324
views
Why and how does the term $\frac{\theta}{32\pi^2}F_{\mu\nu a}\tilde{F}^{\mu\nu a}$ induce electric dipole moment of the neutron?
It is well-known that the operator $$\delta \mathcal{L}_{QCD}=\frac{\theta}{32\pi^2}F_{\mu\nu a}\tilde{F}^{\mu\nu a}$$ violates CP, it can contribute to the neutron electric dipole moment, $d_n$. For ...
- 26.8k
18
votes
1
answer
2k
views
Why is the strong CP term $ \theta \frac{g^2}{32 \pi^2} G_{\mu \nu}^a \tilde{G}^{a, \mu \nu}$ never considered for $SU(2)$ or $U(1)$ interactions?
The Lagrangian one would write down naively for QCD is invariant under CP, which is in agreement with all experiments.
Nevertheless, if we add the term
\begin{equation}
\theta \frac{g^2}{32 \pi^2} ...
- 1,872
9
votes
3
answers
950
views
Are there any serious alternatives to QCD nowadays?
I've read several posts here where people talk about the history of the developement of the theory of strong interactions. And they mention Regge theory, pomerons, S-matrix and so on.
I'm confused ...
- 5,569
6
votes
1
answer
602
views
Proof that QCD is the theory describing strong interactions?
I would like to ask what are the experimental evidences that led to the conclusion that QCD is the right theory to describe strong interactions. I know that some of the key point are the decay of $\...
- 1,707