All Questions
23
questions
1
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0
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77
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Energy stored in the gluon fields -- in a proton, versus, in a pure Yang-Mills mass gap
I was reading this How much of the proton's mass is due to the Higgs field? and finds the discussion says:
As Prof. Strassler explains in the link above, the proton mass is best throught of as ...
- 593
1
vote
2
answers
154
views
The ratio of the Higgs and QCD condensate contribution to valence quark masses
According to https://en.wikipedia.org/wiki/Quark#Mass, the quarks have the following masses.
I suppose these data in the table shows the valence quark masses, such that the uud valence three quark ...
- 4,336
1
vote
0
answers
106
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Do quarks have a non-zero electric dipole moment?
It is written here, in this PSE link that an electron has a measured perfect spherical charge density therefore a zero electric dipole moment (i.e. perfect monopole charge).
My question is, are quarks ...
- 4,170
6
votes
1
answer
857
views
Do gluons mediate the interactions between different flavors of quark?
From some of the quite professional sources (Basics from QCD by CERN; QCD from PDG), the QCD lagrangian is written in the form of
$$
L = \Sigma_{f} \; \bar{\psi}^{(f)} i \gamma^\mu D_\mu \psi^{(f)} + ...
- 165
4
votes
1
answer
129
views
Schwartz loop result in $\bar{c}b\rightarrow \bar{u}d$ EFT
I am trying to reproduce the result of equation $(31.97)$ of Schwart's book Quantum field theory and the Standard Model. The results involves the calculation of the following diagram
where the ...
- 4,118
3
votes
1
answer
183
views
Which quarks can form vacuum condensates?
I faintly remember the rule of thumb that only the up, down and strange quarks can form condensates because their mass is below the QCD scale $\Lambda_\text{QCD}$. But why is that? Where‘s the ...
- 2,648
2
votes
3
answers
697
views
Do quarks annihilate into photons or virtual gluons?
I initially assumed a quark and its anti quark would annihilate into 2 photons (like electrons with positrons) and this does seem to be the case at least sometimes (e.g. For $\pi^0$s).
However in our ...
- 2,604
0
votes
0
answers
179
views
QCD quark self-energy, is the propagator momentum in the right direction?
For the quark self-energy diagram the amplitude is giving by:
The fermion propagator is given by $\frac{i}{\not p + l}$ in the lecture. It is not supposed to be $\frac{i}{\not p - l}$? It's seems ...
1
vote
1
answer
157
views
How do you reconcile quark masses with notion of confinement?
In trying to understand exactly what confinement means, I have been reading 't Hooft s original paper on 2D QCD at large $N$. In the paper he shows that the quark propagator pole is moved to infinity, ...
- 744
4
votes
1
answer
331
views
What was above and below the QCD chiral symmetry breaking temperature?
Above a critical temperature in the Universe, there was probably a phase of unbroken approximate QCD chiral symmetry. Mathematically, the symmetry breaking is triggered when the operators $\bar{\psi}{\...
- 11.8k
5
votes
2
answers
300
views
Theta-dependence of QCD quark condensate for $m=0$
I'm trying to understand the $\theta$-dependence of the following expression for the quark condensate in QCD,
$$ \langle \bar{\psi}\psi\rangle = - \Sigma \cos(\theta)$$
taken from Eqs. (5) and (7) ...
- 1,783
5
votes
1
answer
168
views
Temperature-dependence of quark potential in Abelian lattice gauge theory
I am working with Kapusta's "Finite-Temperature Field Theory" textbook, and am working through the first part of chapter 10. When building the correlator of the two quarks a distance $R$ apart in the ...
- 2,665
1
vote
1
answer
346
views
Commutator of a quark current
In Quantum Chromodynamics, when we take the limit in which the u, d and s quarks have no mass, there exists a global symmetry $G \equiv SU(3)_L \otimes SU(3)_R$ in flavour space. The corresponding ...
4
votes
1
answer
223
views
Well colour me surprised$.$
I was reading Scharf's Quantum Gauge Theories: A True Ghost Story when I stumbled upon the following paragraph (p. 118):
The standard example of a gauge theory with massless gauge fields is the ...
3
votes
2
answers
730
views
Why doesn't infrared slavery provide a proof for quark confinement?
It is well known how and why the running coupling of QCD grows as we reduce energy or equivalently increase distance. Hence, if the effective color charge increases with distance then why doesn't this ...
- 17.8k