We have now added two more quantum fields to our palette, bringing the final total to seven. These matter fields differ from force fields in two important ways. First, they do not exert forces; they create force fields and are acted on by force fields. Second, their spin is ½ (in Planck units). As we will show in the next chapter, this half-integer value leads to the Pauli Exclusion Principle which states that only one field quantum can occupy a given state at a time. This explains why matter quanta behave much more like particles.
There are two types of matter fields: leptons (electrons, muons, neutrinos, etc.) and baryons (neutrons, protons, etc.). In our imaginary color scheme they are represented by yellow and red respectively. The baryon fields have a greater mass (hence the name baryon), and are the only fields that interact with the strong force field. The complete table of fields in QFT is as follows:
|EM||1||Photon (γ)||charged fields||Green|
|Strong*||0||Pion (π+, π–, πo)||nucleon fields||Purple|
|Weak||1||(W+, W–, Zo)||leptons &baryons||Brown|
|Matter – leptons||½||Electron (e), Muon (μ), Neutrino (ν), etc.||N/A||Yellow|
|Matter – baryons*||½||Proton (p)
Neutron (n), etc.
*We will see in Chapter 10 that the strong field and the baryon field are made of more basic but “invisible” fields called quarks and gluons.