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The standard model describes the particle's initial zoo into a smaller set. If I am not wrong quarks were proposed as a solution even before being detected. Is there any reason why we could not describe all the particles in the standard model as coming from a still smaller set? (ideally being described by a single generation of particles). Is there any obvious reason from group theory (or something else) that forbids this?

Note: I am not asking about experimental evidence, but rather, on symmetries and lie algebras, which I just started learning, regardless of if it will ever be possible to reach the energies to test it.

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    $\begingroup$ I'm not sure what kind of answer you're looking for here, exactly - what is group theory supposed to have to do with the composite-ness of particles? $\endgroup$
    – ACuriousMind ♦
    Commented Oct 12, 2022 at 7:50
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    $\begingroup$ I give the link for preons in case of searches and if there is no answer giving it en.wikipedia.org/wiki/Preon $\endgroup$
    – anna v
    Commented Oct 12, 2022 at 9:33
  • $\begingroup$ Linked. $\endgroup$
    – Cosmas Zachos
    Commented Oct 12, 2022 at 10:13
  • $\begingroup$ physics.stackexchange.com/questions/569264/… and Are photons composed particles? $\endgroup$
    – HolgerFiedler
    Commented Oct 13, 2022 at 4:21
  • $\begingroup$ @annav Thanks, that is what I was looking for $\endgroup$
    – user338734
    Commented Oct 14, 2022 at 17:10

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Yes, for example, combining the electroweak and strong interactions as a symmetry-broken phase of a simple gauge theory is the basic idea of Grand Unified Theories (GUT). There are many proposed gauge groups that have some of the properties needed to recover the Standard Model (SM) when their symmetry is broken in a certain way. Even though it is not known as a fact that the SM arises from the broken symmetry of a GUT, there is no known reason it can't be the case, and indeed many researchers actively work on gauge unification.

Further, in supersymmetric (SUSY) field theories, gauge bosons and fermions are all modelled as states of a single type of field. Work on placing the SM in this setting is called the Minimally Supersymmetric Standard Model. Further still, gravitation can be added into the mix with supergravity theories, which arise from the low-energy behaviour of superstring theories.

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    $\begingroup$ I don't understand how this is supposed to relate to the question: GUT theories do not represent the current particles as composites of a smaller set of particles. For instance: the photon, W- and Z- bosons are elementary particles both in the "non-unified" phase of broken electroweak symmetry and the unified phase of unbroken electroweak symmetry. $\endgroup$
    – ACuriousMind ♦
    Commented Oct 12, 2022 at 10:56
  • $\begingroup$ @ACuriousMind The OP doesn't mention composites. It asks if the SM particles could be states of a smaller set. $\endgroup$
    – PM 2Ring
    Commented Oct 12, 2022 at 11:09
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    $\begingroup$ @PM2Ring 1. I don't know what that is supposed to mean, if not that they are composite states of a smaller set of elementary particles. 2. The OP explicitly draws an analogy to the particle zoo being explained via quarks (and that explanation is precisely that all the particles in the zoo were composites of the quarks), so it does mention/ask about composites, even if the post doesn't use that exact word. $\endgroup$
    – ACuriousMind ♦
    Commented Oct 12, 2022 at 11:22
  • $\begingroup$ @ACuriousMind Ok, your point 2 is certainly valid. An example of what I meant is if the neutrino & electron are actually the same particle, but the electron acquires charge (and more mass) due to momentum in the Kaluza-Klein compact dimension. $\endgroup$
    – PM 2Ring
    Commented Oct 12, 2022 at 11:40
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    $\begingroup$ While the space of gauge bosons will have the same dimension after unification, with enhanced symmetry it's no longer possible to distinguish states: we have separate names for the electroweak bosons because they have different properties, but it's fundamentally impossible to tell the difference between two gluons. There's no experiment that will tell the difference between a red-antigreen gluon and a green-antiblue one. The colours are just summation indices for calculating amplitudes. It's reasonable to say there's one type of gluon, and it has an SU(3) symmetry. $\endgroup$
    – Sam Playle
    Commented Oct 12, 2022 at 15:02

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