All Questions
6
questions
0
votes
0
answers
83
views
How does the electroweak interaction and QCD form $SU(2)$ and $SU(3)$?
I'm trying to get a foothold into quantum field theory from a mathematical background. I see the use of $SU(2)$ and $SU(3)$ in gauge theory and wonder the following questions to help me bring QFT ...
- 101
5
votes
1
answer
1k
views
Color symmetry and flavor symmetry in QCD
In QCD, there is an SU(3) color symmetry for each flavor of quark as well as an SU(3) flavor symmetry for $u, d, s$ (although the latter is approximate). Why is there a gauge field for the SU(3) color ...
- 1,653
1
vote
0
answers
137
views
Why is $SU(3)$ and not $U(3)$ the correct gauge symmetry? [duplicate]
If quarks come in three colours $r$, $g$ and $b$ than (neglecting all other quantum numbers and spacial freedom for now) a state of a quark would be a vector in $\mathbb{C}^3$.
If we are now looking ...
- 123
1
vote
0
answers
50
views
The remained global flavor symmetries of massless quarks after gauging electromagnetic $U(1)$
For $N_f$ numebr of massless quarks, we know that there are global symmetries
$$
\frac{SU(N_f)_L \times SU(N_f)_R \times U(1)_V}{Z_{N_f}}
$$
here $U(1)_V$ is the same as $U(1)$-Baryon number ...
- 4,336
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
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