QCD: The Theory of Strong Interactions

Guido Altarelli,Stefano Forte

doi:10.1007/978-3-030-38207-0_4

Abstract

AbstractThis Chapter is devoted to a concise introduction to Quantum Chromo-Dynamics (QCD), the theory of strong interactions. We start with a general introduction where a broad overview of the strong interactions is presented.

Highlights

If the pair is created at one space-time point, for example in e+e− annihilation, and the quark and the antiquark start moving away from each other in the center of mass frame, it soon becomes energetically favourable to create additional pairs, smoothly distributed in rapidity between the two leading charges, which neutralise colour and allow the final state to be reorganised into two jets of colourless hadrons, that communicate in the central region by a number of “wee” hadrons with small energy
In the quantum Quantum Chromo-Dynamics (QCD) theory there is a scale of energy, which from experiment is of the order of a few hundred MeV, its precise value depending on the definition, as we shall see in detail
There are a number of other determinations of αs which are important because they arise from qualitatively different observables and methods

Summary

Introduction

This Chapter 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]). The methods of non perturbative QCD will be introduced, first the analytic approaches and the simulations of the theory on a discrete space-time lattice.The main emphasis will be on ideas with a minimum of technicalities. 2 the QCD theory of strong interactions is an unbroken gauge theory based on the group SU (3) of colour. Quarks and gluons are the only fundamental fields of the Standard Model (SM) with strong interactions (hadrons). 2 for a general introduction to Chaps. The author “G. Altarelli” is deceased at the time of publication. 1See Chap. 2 for a general introduction to Chaps. 2–4 with updated references

Altarelli University of Rome 3, Rome, Italy

Massless QCD and Scale Invariance

The Renormalisation Group and Asymptotic Freedom