Tag Info

New answers tagged

1

The standard chiral lagrangian has a $\pi\to-\pi$ symmetry that forbids processes with an odd number of Goldstone bosons. This is not a symmetry of QCD, however, and these reactions are described by the Wess-Zumino term. The Wess-Zumino term is not a local lagrangian in 4-d, but it can be written as a local lagrangian on a 5-d manifold which has 4-d ...


3

Let us make clear that the problem If proton spin emergence from quarks and gluons is mysterious, why is silver atom spin not? is a modelling problem. The spin both of the proton and the silver atom is measured and known to identify them. John's answer covers it, the energy carried by the virtual quarks and gluons within the proton are much larger ...


6

The binding energy of the electrons in a silver atom is far less than the rest energy of an electron, so there is no ambiguity about the number of electrons in a silver atom. That makes adding up the spins a straightforward business. By contrast, the combined mass of the two up and one down quarks in a proton is about 10MeV (it isn't precisely known) but ...


0

$Λ_{QCD}$ is measured in processes where the strong coupling constant and other measurables vary with momentum scale $Q$. For instance, evolution of nucleon structure functions measured in lepton-nucleon deep-inelastic scattering, heavy quarkonia decays, collider jet physics, electroweak physics at the Z, ... Most results are in the 200 to 300 MeV range. ...


2

Confinement cannot be rigorously shown in QCD with current techniques, because all analytic results in QCD are perturbative and the perturbative expansion breaks down at low energies where the coupling becomes strong. QCD has a negative $\beta$-function, i.e. the Yang-Mills coupling grows at lower energies and becomes weaker at high energies. But the ...


0

Let's begin with $$\langle\Omega|T\{j_{\mu}(x)j_{\nu}(0)\}|\Omega\rangle=\langle\Omega|T\{[\bar{q}(x)\gamma_{\mu}q(x)][\bar{q}(0)\gamma^{\mu}q(0)]\}|\Omega\rangle=$$ $$=\langle\Omega|T\{\bar{q}(x)_a^i(\gamma^{ij})_{\mu}q(x)_a^j\bar{q}(0)_b^k(\gamma^{kl})^{\mu}q(0)_b^l\}|\Omega\rangle=\ldots$$ where I have made the $i,j,k,l$ spinor indices and the $a,b$ ...


1

The paper You refer to is too technical... You can imagine, two bb' quarks in Upsilon meson annihilate via gluons into u---u' (or d---d' or s---s') quark pair. Light quarks move apart from each other with velocity v=0.998c. Due to the confinement, the string of gluonic fields between them is created and it breaks via (qq') pairs creation, producing ...



Top 50 recent answers are included