Can a charged point particle ever have spin zero? If not why?
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Qmechanic
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Derek Seabrooke
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1What exactly do you mean by point particle? only non composite particles? – hof_a Nov 16 '19 at 09:41
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Well yeah I mean it's possible with a composite isn't it? – Derek Seabrooke Nov 16 '19 at 09:42
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Then, atleast in the standard model, the answer is no, as the only fundamental spin zero particle is the higgs boson which has no electric charge. – hof_a Nov 16 '19 at 09:45
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Is there something that prevents such a particle from existing? – Derek Seabrooke Nov 16 '19 at 09:47
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In general I don't think so no, pions are for example charged spin zero particles. We don't need a fundamental charged spin zero particle, although I'm not completly sure if some symmetries of the theory would forbid it. – hof_a Nov 16 '19 at 09:58
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I think this answer to the related SE question should provide enough information. – hof_a Nov 16 '19 at 10:03
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You claim charged Higgs models are unthinkable? – Cosmas Zachos Nov 16 '19 at 12:14
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Yes, there are charged spin zero particles namely the charged pions. However, they are not point particles but rather have a radius comparable to that of a proton. None of the mesons and hadrons are. Only the leptons, the photon, the hypothetical gravitons are point particles. I am not sure of the status of the Higgs boson.
my2cts
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The Higgs boson is in the particle table as a point particle https://en.wikipedia.org/wiki/Elementary_particle in the SU(3)xSU(2)xU(1) standard model – anna v Nov 16 '19 at 14:45
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Similarly with alpha particles, which are "more composite" but has the benefit of being stable. It is also a point particle, as far as real physics is concerned, unless you're doing extremely high-precision spectroscopy of helium, or collision experiments at high (probably MeV) energies. – Emilio Pisanty Nov 17 '19 at 17:07
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@EmilioPisanty The alpha particle has a radius of 3.6 fm, so it should not be called a point particle. However, the OP may have meant a subatomic particle when he wrote that. – my2cts Nov 17 '19 at 18:51
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@my2cts The term "point particle" is silly to begin with - it depends on what physics you're interested in, and no particle can be conclusively shown to have no internal structure or zero radius - so it is pointless to litigate it. I agree that it's as much of a point particle as pions are (i.e., neither of them really is, but both for of them there are broad stretches of useful regimes where they can be considered to be), which is why it's weird to mention pions but not alphas. – Emilio Pisanty Nov 17 '19 at 19:02
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@EmilioPisanty The electron is considered to be a point particle down to $10^{-18}$ m. All physics is in agreement with its radius being zero. It is therefore, justly as far as we know, called a point particle. The term makes perfect sense. – my2cts Nov 17 '19 at 19:23
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@my2cts wait, so you're saying that the electron hasn't been proved to be a point particle, and that the experimental evidence that we have only goes to a finite lengthscale? Then it sounds like you're agreeing with me. – Emilio Pisanty Nov 17 '19 at 19:31
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@EmilioPisanty I state that the electron has no dimension at any scale physically accessible today. Physics that you like or don't like. Please do not twist my words. – my2cts Nov 17 '19 at 19:34
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I think the radius of the electron is a very significant subject and something of a mystery. My pseudonym is not in anyway offensive. I have effectively shared my identity on this forum multiple times by sharing a link to one of my papers. – my2cts Nov 17 '19 at 19:53