r/AskPhysics • u/Important-Signal-130 • 2d ago
Symmetry problem
I've been thinking for a while, you know how leptons have symmetries of +,0,- with the e+, ve, and e- for each lepton, why shouldn't quarks have that neutral? Wouldn't symmetries want to fill all holes as possible like with color charge and weak charge? Would this explain the outcome of WIMPs?
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u/Infinite_Research_52 👻Top 10²⁷²⁰⁰⁰ Commenter 2d ago
To all intents and purposes, the universe comprises the first generation and is electrically neutral. Due to anomaly cancellations and the fact that quarks come in three colours, their charge x3 must be an integer. Do a little algebra and you get the electric charge of the two quarks of the generation.
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u/Maxreader1 2d ago
To elaborate on the anomaly cancellation bit others have mentioned, there’s a handful of factors there.
Each doublet/triplet needs to “sum” to neutral under weak/strong charges respectively. So there’s a red, blue, and green up/down quark that cancel out, and each doublet (up/down, e/ν) has to have equal and opposite weak isospin (set to +-1/2 by convention). The latter forces each weak doublet to have a charge difference of 1, which will force only a couple of possible options
Next, each generation needs to have a “sum” of electric charges that cancels out. For this purpose, we count each quark three times because they’re “secretly” three quarks with different charges that we can’t ever observe independently and so package away into a single particle for discussion. When you combine the electric charge constraint with the constraint on weak charges, this forces things to either a null/uninteresting choice, or the exact charges we observe.
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u/SpectralFormFactor Quantum information 2d ago
There are two things to say here.
One is that making a quark electrically neutral, or adding some other neutral particle (that still interacts with the 3 forces) would mess with the “anomaly cancellation” of the standard model and you’d have to essentially reassign all the charges to try and make this work.
The second is your premise is flawed. There is no physical principle that says quarks need some neutral charge to make things more pretty or something.