Vanadium 50 said:
Getting back on topic, do people still build preon (preons as actual particles) theories? Why?
It is so very tempting though.
Our very terminology points huge arrows in this direction by decomposing fundamental particles in the Standard Model into a bunch of discrete properties that are assigned numbers, which exist in some combinations but not others.
The list I've screen shotted doesn't even include QCD color charge, or whether both left and right, or only left or right parity is available, and particle v. antiparticle distinctions.
A b quark looks like a -1/3 charge preon, plus a single color charge preon, plus a spin-1/2 preon, plus a 1/3 baryon number preon, plus a bottomness preon, plus some composite hypercharge and weak hypercharge particles.
It looks like every other puzzle that science has ever presented to us without actually requiring multi-variable calculus and complex analysis to fathom.
It screams at you that there must be a simpler way! All of our other scientific and life experiences tell us that it feels like there should be some clever way to make it flow from something simpler and deeper.
If it worked for myriad molecules and crystals we encounter in everyday life, it worked for the periodic table of the elements, and it worked for the particle zoo of hadrons, then surely there must be a better way to simplify the 104 possible combinations of color charge, mass, electromagnetic charge, weak interaction charge, spin, parity, and particle-antiparticle combinations (including the graviton, and excluding continuous properties like photon frequency and kinetic energy):
* 3 quark generations x 2 quark EM charges x 3 colors each x 2 parity possibilities x particle/antiparticles for each = 72 discrete quark variants.
* 3 charged lepton generations x 2 parity possibilities x particle/antiparticles for each = 12 discrete charged lepton variants
* 3 neutrino generations x 1 parity possibility x particle/antiparticle for each = 6 discrete neutrino variants
for 90 discrete fundamental fermion variants.
The eight color combinations of gluons, the W+ and W- bosons, one Z boson, the Higgs boson, the photon and the (hypothetical graviton) for 14 discrete fundamental bosons variants.
104 fundamental particles in all.
How can 104 discrete variations of anything be fundamental, our intuition screams?
And there is a prize out there to claim: Reducing the number of experimentally determined constants in the Standard Model.
15 masses, 4 CKM parameters, 4 PMNS parameters, 3 coupling constants particular to the Standard Model, G and the cosmological constant in GR, and the speed of light (it was measured before it was defined, which is why it isn't a round number in meters) and Plank's constant for good measure.
Surely there must be a way to trim down the 30 fundamental constants (really a few less, since a few are not independent of each other due to electroweak unification)!
And, it isn't as if the 104 discrete variants of particle types and 30 fundamental constants show no patterns! There are mass hierarchies and textures and alternative parameterizations. There are correlations between the masses and the mixing angles. There are combinations of properties that are allowed, and combinations of properties that aren't. We already have formulas connecting a couple of the coupling constants to a couple of the masses. So, why shouldn't there be more formulas like that?
Even if your preon model cuts down the number of fundamental particles only minimally, if it can provide a way to calculate many more of those 30 experimentally determined physical constants from first principles, that's a huge win that can provide more precision without more experimental measurements!
And, for those who believe that dark matter particles are a thing and that dark energy has substance, or that SUSY is real, or that there might be inflatons or other motley BSM particles, it offers the reward of a path to identify what those BSM particles could be before we discover them experimentally (and in light of the fact that we may never actually be able to observe them experimentally because the experiments are too hard, at least to complete in our lifetime).
The same incentives, with more sophistication, drive GUT models and string theory, which are basically preon theories for grown ups.
We already know things sufficiently fundamental to know what we need to know to apply the Standard Model and GR to all sorts of absurdly hard problems that are at the very limits of our technological abilities with absurd precision, but it is still so unsatisfying and clunky!
So that's "why" people keep working on preon models.
Is it time well spent?
Probably not.
As Vanadium 50 notes, using the same methods that we used to discovery protons, neutrons and quarks, it takes huge contortions for preons to be real without some sort of Higgs field/gravitational field shielding or something similar to hide hugely massive particles as components of much less massive particles.
But there is also a deep sense that this clunky complexity can't be all that there is to know. The data we have is so organized and structured and fits together so well. It looks like a preon problem! And, preon theories are very inexpensive to research using data collected for other purposes. And, highly respected HEP scientists have tried in the past and published their whimsies, before giving up, so it is respectable, up to a point (even if the numerology monster lurks behind every corner and the experimental constraints get tighter every time we review them anew).
As a result, people keep trying that approach, the same way that they try to climb Mount Everest despite the long line of dead bodies that they have to pass by on the way and knowing that their particular quest isn't likely to change the world in any meaningful way. The data is sitting there, staring us in the face, taunting us!
Preon theory, GUT theory, TOE theory, string theory, and lots of other BSM theorizing is ultimately driven by an unwillingness to accept that what we know now is as good as it gets. Preon theories are just the entry level version of the larger quest.
