Questions tagged [quantum-chromodynamics]
Quantum-ChromoDynamics (QCD) is the quantum field theory believed to describe the strong nuclear force.
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Do we have an analytic calculation to derive $\frac{F^2}{4}\,\text{Tr}\left\{\partial_\mu U\partial^\mu U^{\dagger}\right\}$ from the QCD Lagrangian?
I have studied the quark condensate and chiral perturbation theory. However, I am not sure where the "kinetic term" of the pion
$$\frac{F^2}{4}\operatorname{Tr}\left\{\partial_\mu U\partial^...
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Nuclear physics explained by QCD
I have been studying Particle & nuclear physics and I know that nuclear physics should normally be explained by particle physics. Specifically, I would like to ask if there is any theoretical ...
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What is a polarized/unpolarized parton?
In QCD physics, certain partonic distributions like Generalized Parton Distributions (GPDs) and Transverse Momentum Distributions (TMDs) are defined for the case where the parton is either unpolarized,...
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When to consider and when not to consider the loop contributions from light quarks?
Consider the following Lagrangian:
$$
\tag 1 \mathcal{L} = \frac{\partial_{\mu}a(x)}{f}\sum_{q}\bar{q}\gamma^{\mu}\gamma_{5}q
$$
This is a Lagrangian of the axion-like particles (ALPs) $a$ interacting ...
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Why is the electromagnetic force not an emergent property of the strong force? [closed]
Two up quarks in a proton lead to an imbalance, which results in the proton having the ability to attract electrons. Two down quarks in a neutron lead to balance in the electromagnetic force, leading ...
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How exactly does a proton form from quarks? What is the exact sequence and mechanism?
What are the steps that lead to the bonding of two up quarks and one down quark into a proton? For instance, does an up quark "bind" with a down quark in quark-gluon plasma, which then binds ...
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Why does non-perturbative QCD need to be regularized and renormalized?
The $n$-point correlation functions of QCD, which define the theory, are computed by performing functional derivatives on $Z_{QCD}[J]$, the generating functional of QCD,
$$\frac{\delta^nZ_{QCD}[J]}{\...
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Which hadrons were present after the phase transition from the post-Big Bang QGP?
This question relates to the "hadron epoch" (after the initial quark-gluon plasma, but before the end of baryogenesis).
My understanding is that the phase transition that ends the quark-...
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Why is there only one coupling constant in Yang-Mills theory? Why are gluon self-coupling and gluon-matter coupling constants the same?
Is it non-trivial that the coupling constant $g$ in gluon self-interaction terms is the same as the coupling constant $g$ in gluon-fermion interaction term in Yang-Mills theory?
Pure Yang-Mills theory ...
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How do we known that $\langle \bar{\psi}_i \psi_j\rangle=(250 MeV)^3\delta_{ij}$?
I have started to read the phenomenology of QCD in low energy regime. I understand that, from the QCD renormalization group equation, the QCD becomes nonperturbative theory when energy scale is below $...
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Why do the nucleons interact via strong force even though they are color neutral?
Particles that transform non-trivially under color $SU(3)$ interact via strong nuclear force. However, neutrons and protons, despite being color singlets, interact via the strong force. How do we ...
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Why are gluons massless as their range is finite?
The range of electromagnetic waves and gravitational force is infinity and the particles exchanged during these interactions are photons and gravitons respectively. Both are massless following the ...
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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 ...
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If isospin is only approximately conserved by strong interaction, why do we never see isospin violation?
Due to the mass difference between the $u$-quark and the $d$-quark, SU(2) isospin symmetry is only an approximate symmetry (even in a universe devoid of weak and EM interactions). This suggests to me ...
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Integral of the square of the spectral density in a quantum field theory
The quantity of interest is
$$
\int_0^\infty dE \, \rho(E)^2
$$
where $\rho(E)$ is the spectral density in a Quantum Field Theory. I am wondering whether
it has any physical meaning, and
it can be ...
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