# What does "Standard Model" really refer to?

I am reading the arXiv published paper by Frank Wilczek called "Physics in 100 Years". Apparently, this paper is the printed form of a talk given at Brown University earlier this year (2015).

Right at the start, and in the Appendix, Wilczek clarifies how he is using the name "Standard Model". Quoted from footnote 3 in section 1.1:

The term "Standard Model" has many shortcomings, not the least of which is that it is sometimes used for the electroweak theory, sometimes specifically for the minimal electroweak model, sometimes for the electroweak theory together with quantum chromodynamics, and sometimes for the theories of all four forces.

Wilczek goes on to say that he prefers to use the name "Standard Model" in its original sense, to mean the electroweak theory only (that is, $SU(2)\times U(1)$ gauge theory).

Question: is this distinction in using the name "Standard Model" in this more limited (albeit, original) scope unique to Wilczek or is this common among professional or practicing physicists? I have never heard of it before (showing my ignorance of course) and the Standard Model to me is typically scoped by the full description of all fundamental particles (fermions), forces (bosons), and anti-particle partners.

• Well, Wilczek tells you that you need to look for the context to be sure what you are reading about. To me, it seems the quote already answers your question. May 24, 2015 at 17:42
• Commonly the standard model refers to a still slightly changing model that includes a purely phenomenological description of the color force and the electroweak force. Whether we will still call the model "the standard model" after supersymmetry is included (if it exists, that is) or after some form of dark matter has been identified with a possible extension of it is a question for the science history of the future. It can not be answered, since it's really a choice that physicists will make based on how different a model we will need (or not). May 24, 2015 at 17:45
• I like to say (in a very casual way) that we're currently on Standard Model 2.1beta. If you are still using the buggy 2.0.5 release or earlier versions you should upgrade at the earliest convenient moment. May 24, 2015 at 22:26
• Hi @dmckee. What do you mean by 2.1 beta? May 25, 2015 at 1:50
• @dmckee -- I suppose that Frank Wilczek is still on the early alpha version that focused primarily on the early days of the Electroweak model. I read (just this afternoon, after I posted my original question) that the use of the term Standard Model was first used to describe just the new and emerging electroweak theory. I am guessing that Wilczek's own work on quark confinement and QCD extended the model to include the newer gauge symmetry groups and maybe he still thinks of Standard Model referring to Electroweak only -- the alpha version. May 25, 2015 at 2:36

6 quarks

• Up
• Down
• Charm
• Strange
• Top
• Bottom

6 leptons

• Electron neutrino
• Electron
• Muon neutrino
• Muon
• Tau neutrino
• Tau particle

The force carrier particles (gauge bosons):

• The photon, which mediates the electromagnetic force

• The graviton (as yet unobserved), which mediates the gravitational force

• The W and Z bosons, which mediate the weak nuclear force
• The gluon, which mediates the strong nuclear force

The Higgs boson

These constitute what is referred to as the Standard Model of Particle Physics - a mathematical model of the basic building blocks of matter that make up 4% of the universe according to the Standard Cosmological Model. And of course, every fermion has a corresponding antiparticle. Including those, you would have 12 quarks and 12 leptons.

This is typically what a scientist is referring to when they refer to the Standard Model of Particle Physics. This would be a model of all four fundamental forces.

Sources:

http://physics.info/standard/

http://www.lhc-closer.es/1/6/1/0

• Thanks for your detailed definition of the standard model. However, this really does not answer my question in a satisfactory way. At the end of your answer, you use the phrase "...what a scientist is referring to when they refer to the Standard Model". But, Frank Wilczek is a physicist (aka scientist), indeed, he is a Nobel Prize Winner for his work in quark confinement and QCD. And, he is the one that is saying that the Standard Model refers to Electroweak in his mind. My question is more about whether this a known distinction used by others. May 24, 2015 at 19:01
• And I'm saying it's not. At least, not far as I know. The standard model incorporates all four fundamental forces, which means it incorporates the theories that describe them: QCD for the strong interaction, electroweak for the electromagnetic and weak interactions at high energies, etc.
– user81811
May 24, 2015 at 19:23
• I think that Frank Wilczek is using an earlier more restricted version of the standard model because it serves his purposes. He doesn't need to refer to the whole bit. May 25, 2015 at 16:48