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Why CP symmetry is violated in weak interaction?

  1. Jan 28, 2012 #1
    Please teach me this:
    Why is CP symmetry violated in electro-weak interaction? Is it correct that because of the mass of neutrino is zero(so that the left and righ neutrinos do not mix with each other)?
    Thank you very much in advance.
  2. jcsd
  3. Jan 28, 2012 #2

    Simon Bridge

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    Mass of neutrino is not zero - you seem to be using an old source.

    IFAIK: the correct answer to your question is "we don't know".
    It seems to be a property of the Universe.

    We also have to be careful with "why" questions. Try rewording as a "how" or "what" or something - we leave "why" to philosophers. Thus I have interpreted your question as "what is it about the electroweak interaction that leads to CP violations?"
  4. Jan 28, 2012 #3
    So,from weak interaction theory(meaning massive boson gauge theory) we can not derive the left-righ asymmetry?
  5. Jan 28, 2012 #4

    Simon Bridge

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    It is an empirical result, that is my understanding - yes.

    We can describe it in the math, and several models for underlying behavior have been proposed which give CP violations .... however, the models don't give anything like the correct magnitudes.

    You'll see from the guage theory that the CP violation it is pretty much plugged in. There are some clues in the way the strong interaction is CP-symmetric. You'll meet the different ideas as you progress. I'm worried that if I try to describe them here, I'll just confuse you more or inadvertently mislead you.

    It is possible that things have advanced a bit since I last looked, but a quick trawl suggests "not substantially". I'll leave it to the others to contradict me :)

    Welcome to the edge of known physics.
    Exciting isn't it?

    You should probably find a theoretical physicist in your college working on this.
  6. Jan 28, 2012 #5


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    No, we can't.

    Constructing the SM model Lagrangian with it's U(1)*SU(2) structure in the el.-weak sector and adding the Higgs boson nobody else but nature tells you that you have to have to break chiral symmetry explicitly in the Lagrangian. The mathematical construction itself would work with a chiral symmetric theory as well.
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