All Questions
Tagged with quantum-chromodynamics standard-model
34
questions
19
votes
3
answers
5k
views
Do strong and weak interactions have classical force fields as their limits?
Electromagnetic interaction has classical electromagnetism as its classical limit. Is it possible to similarly describe strong and weak interactions classically?
14
votes
2
answers
2k
views
Why $SU(3)$ and not $U(3)$?
Is there a good reason not to pick $U(3)$ as the colour group? Is there any experiment or intrinsic reason that would ruled out $U(3)$ as colour group instead?
- 558
19
votes
4
answers
2k
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What's the deepest reason why QCD bound states have integer charge?
What's the deepest reason why QCD bound states have integer electric charge, i.e. equal to an integer times the electron charge?
Given that the quarks have the fractional electric charges they do, ...
- 13.1k
11
votes
1
answer
2k
views
Do color-neutral gluons exist?
If I'm correct a quark can change color by emitting a gluon. For example a blue up quark $u_b$ can change into a red up quark by emitting a gluon:
$$u_b \longrightarrow u_r + g_{b\overline{r}}$$
(Here,...
- 392
9
votes
1
answer
2k
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Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?
I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...
- 7,398
2
votes
1
answer
495
views
Similar masses and lifetimes of the $\Delta$ baryons
Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
- 22.1k
2
votes
1
answer
506
views
Understanding type of force interaction in particle decays
Are there any fundamental rules of thumbs that can be used to identify the type of force interaction (weak, electromagnetic, strong) in a particle decay without drawing the Feynman diagrams at the ...
- 310
2
votes
2
answers
696
views
Reasons for choosing $SU(3)$ as the color group vs. $SO(4)$
What are the reasons that $SU(3)$ is used for QCD?
Why wouldn't the simpler & smaller group $SO(4)$ make a better candidate?
- 253
-14
votes
2
answers
3k
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Could the fractional model of Quarks electric charge turn out to be false? [closed]
The delta baryons (also called delta resonances) are a family of subatomic hadron particles which have the symbols $\Delta^{++}$, $\Delta^{+}$, $\Delta^{0}$, and $\Delta^{−}$ and electric charges +2, +...
- 1,025
14
votes
3
answers
2k
views
Bound states in QCD: Why only bound states of 2 or 3 quarks and not more?
Why when people/textbooks talk about strong interaction, they talk only about bound states of 2 or 3 quarks to form baryons and mesons?
Does the strong interaction allow bound states of more than 3 ...
- 17.1k
9
votes
1
answer
807
views
Spontaneous symmetry breaking of anomalous global abelian symmetries and $U(1)$ of QCD
Let me restate the $U(1)$ problem of QCD:
Let us forget about the $s$ quark, and consider the $u$ and $d$ massless. This is
a good approximation since $m_{u,d} \ll \Lambda_{QCD}$. Then $\mathscr{...
- 498
5
votes
1
answer
672
views
Group theoretical reason that Gluons carry color-charge and anti-colorcharge
I was wondering how it is possible to see from the $SU(3)$ Gauge Theory alone that Gluons carry two charges colors: $g\overline{b}$ etc.
Some background:
The W-Bosons (pre-symmetry breaking) form an ...
- 10.1k
3
votes
2
answers
681
views
26
votes
3
answers
5k
views
How (or when) do gluons change the color of a quark?
I know a baryon is only stable when it contains a quark of each color. And as far as I know, the gluon essentially changes the color of a quark and moves onto the next, and this is what holds the ...
- 508
9
votes
2
answers
764
views
Possible implications of Tetraquark/Quark Quartet
Today on Nature's website appeared a news about the discovery of a quark quartet (formed from two quarks and two antiquarks). They say that this particle containing four quarks is confirmed. This is ...
- 2,158