## QCD

It is believed that Quantum Chromo Dynamics is the fundamental theory of strong interactions
between quarks due to gluon exchange.

The fundamental charge strong interaction forces are coupling to is the colour charge for
which there are several strong experimental evidences.

Following the gauge principle already discussed for QED one can construct QCD
as a non-Abelian quantum gauge theory based on local
SU(3)_{Colour} transformations. In contrast to QED, the gauge bosons, the gluons,
also carry colour charges leading to self-interactions of the gluons.

The Feynman rules for QCD are discussed by applying them to some selected
simple processes.

Then, some properties of bound states of a quark and an antiquark, a.k.a.
Quarkonia, are investigated to illustrate some of
the symmetries underlying the bound states of QCD.

A very important characteristics of QCD, related to the occurence of its quanta in bound states
only is discussed in the section 'Asymptotic Freedom'.

The chapter closes with a discussion of multiple gluon radiation and a short presentation
of models for the fragmentation of quarks and gluons into hadrons.