All Questions
Tagged with quantum-chromodynamics particle-physics
207
questions
2
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1
answer
171
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Physical significance of the reality of an ${\bf N}$ representation: how the nature of interactions is affected?
Background The fundamental representation of ${\rm SU(N)}$ is denoted by ${\bf N}$ and the conjugate of the fundamental is denoted by ${\bar{\bf N}}$. If the representation ${\bf N}$ is related to ${\...
- 26.8k
-1
votes
1
answer
214
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What does it mean by active quarks?
Do the active quarks mean valence quarks? Or we can also consider other quarks, like when there are offshell-quarks produced from gluons by pair production processes?
For example: how the active quark ...
- 337
4
votes
2
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545
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Could a proton be produced using the dynamical Casimir effect?
According to the standard model, would it be theoretically possible to emit protons or other complex particles from the vacuum using the dynamical Casimir effect? Or is it only possible to emit ...
- 609
2
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0
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783
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QCD energy scale $\Lambda_{\rm MS} $, $\Lambda_{\rm QCD}$, ...?
Why there seems to be different conventions of QCD energy scales? Is that due to the running coupling?
For example in Wikipedia https://en.wikipedia.org/wiki/Coupling_constant#QCD_scale:
$$
\Lambda_{\...
- 4,336
4
votes
3
answers
272
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Why quarks are confined? Why can't they be found in unbound states?
No one has observed before a "free" quark, i.e. a quark in an unbound state. According to one paper, I read that $p\bar{p}$ collision produce unbound $t\bar{t}$ pair which quickly decay into ...
- 557
2
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1
answer
231
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Connections between conformal field theory and particle physics
I'm wondering if one could use conformal field theory to predict any facts in (experimental) particle physics?
I think CFT shares some similarities with QCD, but I'm not sure if one could use CFT to ...
- 547
0
votes
1
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68
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If quark current masses were equal, processes like $dd \to ss$ would be forbidden?
The QCD lagrangian has a $SU(N_{f})$ vectorial symmetry, which is explicitly broken by the difference in quark current masses. If this symmetry was exact ($m_{u}=m_{d}=m_{s}$...) the charges ...
- 125
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42
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How to expand the QCD loops in terms of infrared scale for matching with heavy quark effective field theory
According to Manohar:"argument applies almost without change to a practical example,the derivation of the HQET Lagrangian to one-loop."
on page 37 of the following paper on effective field ...
- 1,268
5
votes
1
answer
86
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Emergence of Dual Resonance model from QCD
This question is about getting to understand better what the Dual Resonance (DR) model actually managed to successfully predict or model from the nuclear interactions, in the context of understanding ...
- 14.5k
0
votes
1
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130
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Conservation of left-handed quark current
I'm reading about the Operator Product Expansion in Gelis's A Stroll Through Quantum Fields section 7.4.2. As an example, he's using the product of currents
$$A_1^\mu = \overline{d}_L\gamma^\mu u_L$, ...
- 364
0
votes
1
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108
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Can a gauge theory with $SU(2)_{left}*SU(2)_{additional}$ symmetry contain confinement?
Consider a gauge theory with $SU(2)_{left}*SU(2)_{additional}$ symmetry.
By $additional$, I mean adding a new symmetry between an electron and a quark(like up quark and electron forming a doublet).
...
- 1,268
0
votes
2
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210
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Strong force coupling
My lecture notes write that the coupling constant for the strong force goes to infinity as the distance goes to infinity.
However the range of the strong force is said to be small.
If the strength ...
- 127
2
votes
1
answer
204
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Why do we need two gluons for the decay $ϕ \to 2K$?
The Feynman diagram for the decay $\phi \to K^+K^-$ usually depicts two gluons. (This can be seen e.g. on Wikipedia).
Why do we need two gluons, instead of just one?
- 2,648
5
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1
answer
1k
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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
2
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0
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106
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How does neutron radiation affects a body? [closed]
My question involves two aspects of the same thing: how does neutron radiation affect the particles in our body.
• First of all: How does the effects happen, from a quantum perspective?
• Second, ...
- 133