Questions tagged [quantum-chromodynamics]
Quantum-ChromoDynamics (QCD) is the quantum field theory believed to describe the strong nuclear force.
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Is QCD free from all divergences?
On page 8 in The Triumph And Limitations Of Quantum Field Theory David Gross makes the following comment:
"This theory [QCD] has no ultraviolet divergences at all. The local (bare) coupling ...
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Massive Gauge Bosons without Higgs fields
In a possible theory like our Standard model but without a Higgs i.e.:
$$ \mathcal{L}=i\bar{\Psi}_f\gamma_\mu D^\mu\Psi_f-\text{Tr}[G^b_{\mu\nu}G^{b\,\mu\nu}] $$
where $b,f$ run over the typical ...
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Why are the Higgs phase and the confinement phase identical in Yang-Mills-Higgs systems?
If we couple a Yang-Mills theory with a Higgs field and some quarks in the fundamental representation, we can have a Higgs phase and a confining phase. However, they are indistinguishable. The Wilson ...
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How does Delta baryon decay conserve angular momentum?
I'm a chemist so bear with me:
I understand the Delta baryons $\Delta^{+}$ and $\Delta^{0}$ to be in some sense spin (and isospin) quartet states of the proton and neutron. These can decay straight ...
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Why are the even and odd Regge trajectories degenerate?
This is an old classic which I don't think ever got a clear answer. The Gribov-Froissart projection that gives the relativistic version of Regge trajectories treats even angular momentum differently ...
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Measuring and calculating free quark masses
Particle data book contains masses of the free quarks. I wonder, how do experimentalists determine the masses of the free quarks even though they are trapped inside hadrons (except perhaps in quark-...
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Most trivial neutral pion decay
Literature states neutral pion decay by QED cannot occur directly because the pion is uncharged.
However, I cannot see why Photons are not allowed to interact with the Quarks directly.
Please ...
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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 ...
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What is relevant for Yang-Mills theory below $d = 4$?
There are two ways to write the Lagrangian for Yang-Mills, differing by the scaling of the Yang-Mills field. Fancy theorists tend to write
$$S = \int d^dx \, \frac{1}{4e^2} \, \text{tr}(F^2)$$
while ...
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Glueball mass in non-abelian Yang Mills theory
How can the glueball mass be calculated in Yang-Mills theory?
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Question about the linear sigma-model
Suppose the linear sigma-model lagrangian:
$$
L = \bar{N}(i\gamma_{\mu}\partial^{\mu}-g_A \phi)N + |\partial_{\mu}\phi|^{2} - V(|\phi|) - c\sigma ,
$$
where
$$
N = \begin{pmatrix} p \\ n\end{pmatrix}, ...
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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}{\...
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Why quarks in the fundamental and gluons in the adjoint?
I have been told that in gauge theories
“fermionic matter goes in the fundamental rep of $SU(N)$, while gauge fields go in the adjoint rep”.
I understand how this works, and for instance, in QCD,...
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What are chromoelectric and chromomagnetic fields?
Are they the normal electric and magnetic fields from Maxwell fields? Or are they just the corresponding components from $G_{\mu\nu}^a$ (the gluon fields), say chromoelectric fields are simply $G_{0i}^...
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