4 QCD: The Theory of Strong Interactions
85
Fig. 4.1 Feynman rules for QCD. The solid lines represent the fermions, the curly lines the gluons,
and the dotted lines represent the ghosts (see Chap. 2). The gauge parameter is denoted by λ. The
3-gluon vertex is written as if all gluon lines are outgoing
where
C F =
1
N C
A
t
A t
A
=
N 2
C − 1
2N C
(4.6)
with N C the number of colours (N C = 3 in QCD). The scale dependence of
α s (the distance r is Fourier-conjugate to momentum transfer) will be explained
in detail in the following. The understanding of the confinement mechanism has
much improved thanks to lattice simulations of QCD at finite temperatures and
densities. The slope decreases with increasing temperature until it vanishes at a
critical temperature T C . Above T C the slope remains zero. The phase transitions
of colour deconfinement and of chiral restauration appear to happen together on the
lattice. A rapid transition is observed in lattice simulations where the energy density
(T ) is seen to sharply increase near the critical temperature for deconfinement and
chiral restauration. The critical parameters and the nature of the phase transition
85
Fig. 4.1 Feynman rules for QCD. The solid lines represent the fermions, the curly lines the gluons,
and the dotted lines represent the ghosts (see Chap. 2). The gauge parameter is denoted by λ. The
3-gluon vertex is written as if all gluon lines are outgoing
where
C F =
1
N C
A
t
A t
A
=
N 2
C − 1
2N C
(4.6)
with N C the number of colours (N C = 3 in QCD). The scale dependence of
α s (the distance r is Fourier-conjugate to momentum transfer) will be explained
in detail in the following. The understanding of the confinement mechanism has
much improved thanks to lattice simulations of QCD at finite temperatures and
densities. The slope decreases with increasing temperature until it vanishes at a
critical temperature T C . Above T C the slope remains zero. The phase transitions
of colour deconfinement and of chiral restauration appear to happen together on the
lattice. A rapid transition is observed in lattice simulations where the energy density
(T ) is seen to sharply increase near the critical temperature for deconfinement and
chiral restauration. The critical parameters and the nature of the phase transition