The quarks will be major characters in our story and are the fundamental objects participating in
strong interactions. Like the electrons, they are simple structureless (as far as we know) spin-1/2
particles. Therefore in a relativistic theory, they are described by Dirac spinors ψα(x) with four
components α = 1,..., 4, which are functions of the space-time coordinates x
µ = (t,x,y,z). If
quarks did not interact with other particles or fields, they would obey the free Dirac equation,