All Questions
9
questions
2
votes
1
answer
450
views
Why, in QCD, are quarks in the fundamental representation of $SU(3)$?
QCD is built from the notion that Dirac's Lagrangian should be invariant under gauge colour transformations.
Here, quarks are elements of $\psi_{\alpha,f,c}(x)$, where $\alpha$, $f$ and $c$ stand for ...
- 343
0
votes
2
answers
91
views
Quantum chromodynamics - why are there no $rrb$ or $ggr$ terms?
$$\Psi_{colour}^{qqq} = \frac{1}{\sqrt{6}}(rgb + gbr + brg -grb - rbg - bgr)$$
My lecturer stated that there cannot be any $rrb$ or $ggr$ terms in the expression above. I would like to understand what ...
- 13
2
votes
2
answers
68
views
How do we understand the ${\bf 3}$ of $Q_L({\bf 3}, {\bf 2})_{1/3}$?
A left-handed quark doublet of the Standard Model is specified as $Q_L({\bf 3}, {\bf 2})_{1/3}=(u,d)^T$. I have a problem understanding this quark doublet as a triplet of ${\rm SU}(3)$. Any help? I ...
- 11.8k
0
votes
0
answers
221
views
What is the application of dimension $6$ representation of $SU(3)$ in particle physics?
As we know, the $uds$ transforms in fundamental representations of $SU(3)$. It has the antifundamental partner. According to representation theory,
$$
\mathbf{3} \otimes \mathbf{\bar{3}}= \mathbf{8} \...
4
votes
1
answer
2k
views
$SU(3)$ Color Symmetry
I have following (maybe a bit general) question about the $SU(3)$-symmetry of color by quarks:
If I consider the analogy to the $SU(2)$-symmetry of isospin $I$ crucially it concers the conservation ...
- 1,395
5
votes
2
answers
664
views
Quark model extension to all six flavors
Gell-Mann's $SU(3)$ quark model is extremely successful at describing the bound states of the three light quarks $u,d,s$. The bound states fall neatly into the irreducible representations of $\...
0
votes
2
answers
1k
views
Why are 3 colors used in QCD?
The mapping of strong charge to RGB left me believing that there are only 3 conserved quantities in QCD. I recently came to the understanding that there are in fact 8 conserved quantities, as ...
- 403
0
votes
0
answers
456
views
Non-singlet and singlet flavor combination [duplicate]
In the perturbative QCD, specific partonic distribution functions (pdf) linear combination is called "flavor singlet" or "flavor nonsinglet" combination.
What is the combination, and why are they ...
- 857
2
votes
2
answers
552
views
Pentaquark spin prediction
Is there a straightforward way to see what the spin of the recently-discovered pentaquark states should be, from the representation theory of $SU(3)\times SU(2)\subset SU(6)$? I can see that from the ...
- 4,418