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Matter of generation 0

  1. Jun 27, 2006 #1
    Hello,

    I'm not an expert, hardly a novice, in physics but still had some thoughts which might be worth shooting at.

    The stable matter of our universe consists mostly of matter made of electrons and up/down quark based particles (generation 2), which is described in the standard model. The difference with the generation 2 (muon electrons and charm/strange quarks) and generation 3 (tauon electrons and top/bottom quarks) matter is that those are unstable in our universe and decay rapidly.

    Why is generation 1 matter stable and 2 and 3 not? Is there a theory which could explain this?
    Or which fundamental laws or constants should be different so there would exists a stable generation 2 universe?

    Personally I think a stable generation 2 or even 3 universe might be possible. This gives the thought that if such a stable generation 2 universe exists, would stable generation 1 matter in that universe be detectable using equipment made of generation 2 matter? Could those two types of matter interact?

    Back to our universe which still consists of generation 1 matter but which might be similar to the generation 2 universe. Could there be a stable generation 0 lower energy matter, I do not mean neutinos (which are of generation 1), which could exist and have effect on our universe like for example being dark matter. Because of the low energy of this matter it is very difficult to detect, I think.

    Has someone had similar thought of made some calculation regarding this.


    Regards,
    Rebbyte
     
  2. jcsd
  3. Jun 27, 2006 #2

    arivero

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    You forgot the neutrinos. Having neutrinos around, do you still think that the second generation can/could be stable? And a trickier question... can you imagine some way to build an stable fourth generation?
     
  4. Jun 27, 2006 #3

    mathman

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    One part of the explanation is that generation 2 and 3 particles (except neutrinos, which are rather peculiar) can decay into generation 1 particles, but generation 1 particles have nothing to decay to.
     
  5. Jun 28, 2006 #4
    Every answer gives new questions.

    If there would be generation 0 particles, but generation 1 particles do not decay to them because they are stable, what makes them stable? Only that there is no lower energy level matter to decay to (as far as we know)? However if generation 0 would exist can there be something else holding it stable?
    Can generation 2 particles only be stable in a universe where generation 1 particles do not exist? Or is there some other rule present which makes them stable or not? A sort of terrace on which the particles are kept stable.
    Might generation 1 particles not be stable? Can protons decay into unknown (generation 0) matter/energy which has not been detected yet (Super-Kamiokande). And might the stability of matter (generation 1 to 3) be related to it’s energy level?

    Regards,
    Rebbyte
     
  6. Jun 28, 2006 #5

    selfAdjoint

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    This is the mass-gap problem; To show that there is a minimum energy (mass) greater than zero in a gauge theory (the standard model is such a theory). To prove there exists a mass gap in Yang-Mills theory, the prototype of all gauge theories, is one of the Clay Millenium Problems, for which a millionbucks reward is offered. If there is no mass gap then whatever lowest mass you have found may have a yet lower mass that you haven't found, and so on ad infinitum, trending to zero. That's an energy blow up that would make the theory invalid. Google IR catastrophe.
     
    Last edited: Jun 28, 2006
  7. Jun 28, 2006 #6

    arivero

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    Could you agree what a generation is? and then we can start discussing. In the current model of Particle Physics, a generation is a set of particles that held representations of the Standard Model group in a way that they guarantee the absence of anomalies. This amounts to have one neutrino, one charged lepton and two tri-coloured quarks with charge 1/3 and 2/3 of the one of the electron.

    Now, it can alway happen that the charged lepton transforms to neutrino creating a W- particle, and that this W- particle desintegrates on a pair chergedlepton plus neutrino of any generation. So if the mass of the neutrinos is very small compared to the mass of the charged leptons, only one of the charged leptons can be stable. If we want both the electron and a 0-generation lepton to be stable, then the neutrino of the 0-generation must have a mass higher than the mass of the electron in order to block this disintegration process.

    Of course you can have particles beyond the generation schema, and in fact there are a lot of proposals in this sense. Axions, for an instance.
     
    Last edited: Jun 28, 2006
  8. Jun 28, 2006 #7

    arivero

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    Of course. The disintegration rate goes as the quintic power of the mass of the particle. Textbook thing.
     
  9. Jun 28, 2006 #8

    arivero

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    Hmm not exactly. The mass gap problem does not address the issue of the mass of fundamental fermions, and he was asking about generations of such fermions. What the standard model mass gap problem should proof is the existence of a bound value for the mass of pion, proton, and any other SU(3)-bound object.

    Incidentally, the quintic rule mentioned above works also for SU(2) decaying composite objects, while U(1) decaying hold a cubic power rule (and this one is not a textbook think, but empirical). SU(3) decays are too fast and too mixed to give a precise relationship between stability and energy level.
     
    Last edited: Jun 28, 2006
  10. Jun 29, 2006 #9
    I start getting the picture and also very much start to think there will no fermions of a lower energy than of generation 1.
     
  11. Jun 29, 2006 #10

    arivero

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    That is almost the point. No exactly any fermion, but fermions in the sense of fermions acting under the standard model forces. For instance time ago there was a lot of talk on the "sterile neutrino", a neutrino not able even to interact with the Z0 boson. And some other particles, usually bosons, are proposed from time to time (mostly as candidates to dark matter, as you guessed). But if the fermions are able to interact via the standard model SU(2)xU(1) force, then you can not have a pair "0electron, 0neutrino" having total mass lower than the 1st (nor 2nd, nor 3rd) generation mass.

    Moreover, the Z0 boson disintegrates into any generation pair of neutrino/antineutrino with mass lower than the one of this Z0. So we are pretty sure there are no more neutrinos with a mass lower than Z0/2.

    The only exit if you want a 0electron ligher than the standard electron is to postulate that its corresponding neutrino has a mass greater than 45 GeV :Eek:
     
    Last edited: Jun 29, 2006
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