Chapter 4
QCD: The Theory of Strong Interactions
Guido Altarelli and Stefano Forte
4.1 Introduction
This Chapter 1 is devoted to a concise introduction to Quantum Chromo-Dynamics
(QCD), the theory of strong interactions [1–3]. We start with a general introduction
where a broad overview of the strong interactions is presented. The basic principles
and the main applications of perturbative QCD will be discussed first (for reviews
of the subject, see, for example, [4–6]). Then the methods of non perturbative QCD
will be introduced, first the analytic approaches and then the simulations of the
theory on a discrete space-time lattice.The main emphasis will be on ideas with a
minimum of technicalities.
As discussed in Chap. 2 the QCD theory of strong interactions is an unbroken
gauge theory based on the group SU (3) of colour. The eight massless gauge bosons
are the gluons g A
μ and matter fields are colour triplets of quarks q
a
i (in different
flavours i). Quarks and gluons are the only fundamental fields of the Standard Model
(SM) with strong interactions (hadrons). As discussed in Chap. 2, the statement that
The author “G. Altarelli” is deceased at the time of publication.
1 See Chap. 2 for a general introduction to Chaps. 2–4 with updated references.
G. Altarelli
University of Rome 3, Rome, Italy
S. Forte ()
Dipartimento di Fisica, Università di Milano, Milano, Italy
© The Author(s) 2020
H. Schopper (ed.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-38207-0_4
83
QCD: The Theory of Strong Interactions
Guido Altarelli and Stefano Forte
4.1 Introduction
This Chapter 1 is devoted to a concise introduction to Quantum Chromo-Dynamics
(QCD), the theory of strong interactions [1–3]. We start with a general introduction
where a broad overview of the strong interactions is presented. The basic principles
and the main applications of perturbative QCD will be discussed first (for reviews
of the subject, see, for example, [4–6]). Then the methods of non perturbative QCD
will be introduced, first the analytic approaches and then the simulations of the
theory on a discrete space-time lattice.The main emphasis will be on ideas with a
minimum of technicalities.
As discussed in Chap. 2 the QCD theory of strong interactions is an unbroken
gauge theory based on the group SU (3) of colour. The eight massless gauge bosons
are the gluons g A
μ and matter fields are colour triplets of quarks q
a
i (in different
flavours i). Quarks and gluons are the only fundamental fields of the Standard Model
(SM) with strong interactions (hadrons). As discussed in Chap. 2, the statement that
The author “G. Altarelli” is deceased at the time of publication.
1 See Chap. 2 for a general introduction to Chaps. 2–4 with updated references.
G. Altarelli
University of Rome 3, Rome, Italy
S. Forte ()
Dipartimento di Fisica, Università di Milano, Milano, Italy
© The Author(s) 2020
H. Schopper (ed.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-38207-0_4
83