From: g.scholten@nospam.gmx.de
James Goetz wrote:
> Gluons bond quarks into baryons (i.e., protons and neutrons).
More precisely, strong interaction binds quarks into baryons. Or
in other words: gluons fields, i.e. fields of which gluons are field
quanta (like photons are of the electromagnetic field), bind quarks
into baryons. Using perturbation theory to calculate transition
amplitudes caused by this strong interaction, one can say that
quarks "exchange virtual gluons". More precisely: in perturbation
theory, one uses the S-matrix to do calculations, and terms in the
S-matrix can be graphically depicted by Feynman diagrams, with inner
lines that are related to virtual particles. In lowest order of
perturbation theory, there is one inner gluon line between two
quarks. In higher orders, there are higher numbers of inner lines.
Sad to say, strong interaction contradicts one core aspect of
perturbation theory, namely that higher orders yield lower contributions
to transition amplitudes. For other interactions, like weak interaction
or electromagnetic interaction, the main contributions come from
lowest order, but strong interaction is that strong that all orders
of perturbation theory yield comparable contributions. Take e.g.
electromagnetic interaction: there, the coupling constant is 1/137,
yielding a factor (1/137)^n for the n-th order, but for strong
interaction, the coupling constant is approximately 1. So, Feynman
diagrams with one inner gluon line contribute as much as diagrams
with 2, 10 or 100 inner gluons lines.
Therefore, perturbation theory is not a very appropriate method to
describe strong interaction. A more appropriate approach is Lattice
Gauge Theory. This approach, however, does not yield virtual
particles (gluons for strong interaction) as interaction intermediators.
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