All Questions
Tagged with quantum-chromodynamics quantum-mechanics
31
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Colour Factor in QCD Pair Annihilation
My question occurred when I was reading Introduction to Elementary Particles by David J. Griffiths. In chapter 8, part 8.5, he is calculating the colour factor of quark-antiquark annihilation.
My ...
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-1
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2
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206
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How exactly does a proton form from quarks? What is the exact sequence and mechanism?
What are the steps that lead to the bonding of two up quarks and one down quark into a proton? For instance, does an up quark "bind" with a down quark in quark-gluon plasma, which then binds ...
- 29
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20
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Diquark propagators in color superconductivity
I’m studying color superconductivity referring to “The Phases of Quantum Chromodynamics From Confinement to Extreme Environments” by John B. Kogut and Mikhail A. Stephanov (link).
In chapter 9, the ...
- 165
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1
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136
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Are all mass eigenstates also spin eigenstates?
Is there a rigorous way to show that a mass eigenstate of a particle must also be an eigenstate of the total spin operator? If this wasn't true, you could imagine that a composite particle in a mass ...
- 867
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28
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Correlation of the strong force with fractional charges? [duplicate]
As far as we know the quarks are not free not because of their fractional charges but because of the independent strong force interaction that grows with distance within the radius of the proton or ...
- 4,170
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89
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Color factor in Breit-Wigner formula
We are given the Breit-Wigner formula for the process $ud\rightarrow W\rightarrow e\nu$ as $$\sigma=\frac{1}{N_c^2}\frac{2J_W+1}{(2J_u+1)(2J_d+1)}\frac{4\pi}{s}\frac{\Gamma_{ud}\Gamma_{e\nu}}{(\sqrt{s}...
- 2,122
3
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1
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557
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How exactly do quarks suppress gluon fluctuations?
In both this Veritasium Video and this answer it is said that Quarks suppress gluon fluctuations, thus creating a so-called 'flux tube' which is what binds the gluons together (as explained in both ...
- 3,778
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130
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What happens to an electron when it radiates a photon?
I recently came across this Feynman diagram:
For a more simplistic diagram, I suppose even this would be adequate:
As you can see in these diagrams, they radiate these virtual photons. The virtual ...
- 126
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96
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What is the real problem in the free body problem?
Ions are produced when an EM neutral atom gains EM charge by gaining or losing electrons, by collision with other charged particles or photons.
The study of such collisions is of fundamental ...
- 29k
2
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1
answer
89
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Quark-Gluon Plasma vs QCD binding energy
The binding energy of nucleons is on the order of around 900 MEV. Yet, Quark-Gluon plasma is observed at around 175-300MEV. This doesn't seem to make any sense - how can only 300 MEV worth of energy ...
- 545
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160
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Why are gluons necessary?
I understand that quarks are attracted to each other when they have different color charges to become neutral. I also understand that gluons are the exchange particles of the strong force by switching ...
2
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1
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727
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What's a "colour triplet fermion"?
I'm not a big fan of Science Alert, but this recent piece about the so-called SMASH model, whose gory details are apparently presented in arXiv:1608.05414 seems reasonable. I'm curious about this "...
- 134k
4
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1
answer
1k
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Callan-Gross relation validity
The inelastic electron-proton scattering cross section can be written as
$$\frac{d\sigma}{dE_2d\Omega}=\frac{\alpha^2}{4*E_1\sin^4{\frac{\theta}{2}}}(W_2\cos^2{{\frac{\theta}{2}}}+2W_1\sin^2{{\frac{\...
- 263
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2
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442
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Can quarks have anti-colors? [closed]
What is the reason that the color properties we call red, green and blue have become tied to quarks, while what we call anti-red, anti-green and anti-blue has become tied to anti-quarks? Do note that ...
- 415
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1
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386
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What is a "dynamically generated scale" physically?
A theory like QCD with massless quarks in four dimensions has no explicit mass parameters in its classical Lagrangian. At the quantum level however, instead a mass scale Λ is generated dynamically at
...
- 3,872
5
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2
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404
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Valence sea quarks parton distribution functions
There's somethin from Thomson (Modern Particle Physics) that I am a little mythed by.
Section 8.4.3, eq. 8.3 is given as
$$
\frac{F^{\mathrm{en}}_2(x)}{F^{\mathrm{ep}}_2(x)}=\frac{4d_{V}(x)+u_{V}(x)+...
- 1,634
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140
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Hadron Annihilation - what happens with the constituents
When a Hadron and its antimatter equivalent annihilate, what happens to the QCD "soup" (for lack of an appropriate term) from each?
Eg, the valence quarks in a proton - antiproton event, to they pair ...
- 825
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2
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728
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If proton spin emergence from quarks and gluons is mysterious, why is silver atom spin not?
A recent Scientific American article brought up an old issue, which is this: According to quantum chromodynamic models, the emergence of exactly 1/2 unit of spin in a proton (or a neutron, or any ...
- 22.1k
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1
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809
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The counting of all possible baryons quark combinations
I would like to ask how do you count the number of possible quark combination that could possibly exist in a baryon. I know certain spin symmetry or orbital momentum symmetry have to be conserved. But ...
- 1,239
16
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2
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1k
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QCD and QED with unlimited computational power - how precise are they going to be?
My question is about quantum algorithms for QED (quantum electrodynamics) computations related to the fine structure constants. Such computations (as explained to me) amounts to computing Taylor-like ...
- 2,073
3
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1
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146
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Large wavelength limit of gluons
Does there exist a classical limit of QCD? I mean in the sense of wave particle duality of eg photons. Is there any similar thing for gluons?
- 5,569
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If virtual particles have negative mass why do they contribute positive mass to atoms?
According to Lawrence Krauss, atoms containing in our body consists of merely 10% (if I remember correctly) of our total mass. The rest come from virtual particles popping in and out of existence from ...
- 197
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Is this a photograph of Surface Plasmon Resonance?
Does this photograph depict surface plasmon resonance?
PHOTO 1 - Ellipsometric style photograph produces blue-green and purple resonance waves from nanogold-like tubule.
PHOTO 1 was cropped from ...
- 96
4
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1
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414
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The relation between classical and quantum vacua
First let me clarify what I mean by vacuum.
Suppose we are concerned with a theory of fields $\phi ^i$ defined on a stationary globally hyperbolic spacetime $M$ (I want the spacetime to be stationary ...
- 8,540
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63
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Quantum fluctuations in the non-relativistic limit
Is there any way to describe quantum fluctuations in ordinary quantum mechanics? For instance, a proton fluctuating into a proton-$\pi^0$ state and then back to a proton?
What are the relevant ...
- 5,569
8
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2
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436
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No non-trivial UV asymptotically free and IR free
How it could be proven that a non-trivial theory cannot be both asymptotically free and IR free (g=0 both in the UV and IR with some interpolating function in between)? This is of course contrary to ...
- 1,707
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1
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249
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What is quark transverse momentum?
When you google my question you get something on the order of 400 000 results but none of them explains how it is defined (No I didn't check them all).
I know what the words quarks, transverse and ...
- 5,569
2
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1
answer
1k
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What is the nucleon axial charge?
Can someone point me to a short definition of what the nucleon axial charge is?
- 5,569
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2
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237
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Neutral pions and chromodynamics
$\pi^0$ particles are either up-antiup or down-antidown (or strange-antistrange?) They must be opposite colors to preserve neutrality. Why don't the opposite quarks annihilate?
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Charge in terms of wavefunctions
For a charged quantum particle, say, an electron or a quark, how in the particle's wavefunction is the electric charge represented? Is it truly possible to represent electric charge using the wave ...
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