The Strong Interactions and QCD

The modern theory of the strong interactions is quantum chromodynamics (QCD). The basic ingredient is that each of the six flavors or types of quark, u, d, s, c, b, and t, has an additional quantum number color, which takes the values α = 1, 2, 3, or red (R), green (G), blue (B), and that there is an unbroken non-chiral SU(3) gauge symmetry acting on the color index. Thus, there are 8 massless gauge bosons (gluons), Gⁱ , and a strong gauge coupling g_s and strong fine structure constant https://www.w3.org/1998/Math/MathML"> α s = g s 2 / 4 π https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315170626/2130fe5e-77bd-49fa-b8c1-fbaea94dfb59/content/equ_1815.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> . In this chapter we survey the properties of the strong interactions and QCD, especially the symmetry aspects at short and long distances. For more detailed treatments, see, e.g., (Brock et al., 1995; Pich, 1999; Ellis et al., 2003; Sterman, 2004; Kronfeld and Quigg, 2010; Salam, 2010a; Skands, 2013; Altarelli, 2013; Trócsányi, 2015; Patrignani, 2016). For the historical development, see, e.g., (Gross, 2005; Leutwyler, 2014; Fritzsch and Gell-Mann, 2015).