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Leptogenesis and see-saw before EWSB

  1. Nov 3, 2014 #1
    Hi everyone

    Leptogenesis models create a lepton asymmetry via the decay of heavy RH neutrinos into leptons and a higgs.

    Many models of leptogenesis happen before EWSB

    The coupling for this interaction is the yukawa coupling between the heavy neutrino and the higgs and lepton doublet. This comes from the dirac mass term introduced by the see-saw model.

    What I don't understand is how this interaction, which comes about due to the yukawa couplings with the higgs, can occur before EWSB.

    m_D = vh happens after EWSB ... but we seem to be using it in an interaction before EWSB

    If anyone could shed some light on that would be great.

  2. jcsd
  3. Nov 3, 2014 #2


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    The coupling is always there, even before EWSB. What changes upon symmetry breaking is that the Higgs field takes a vev, which in turn makes the coupling induce both the Dirac mass term as well as a particular structure for the interactions.
  4. Nov 3, 2014 #3

    Thanks for the reply. I was thinking of this in the wrong direction.. I was thinking more of a Dirac mass term being fundamental and existing before EWSB and then this causing a term with the couplings after the symmetry breaking. But of course its the other way around.

  5. Oct 21, 2016 #4
    I have a slightly related question (although I guess its more general in the sense it could apply to any particles before EWSB)

    Before EWSB the neutrinos do not have mass. But to thermally produce the heavy neutrinos, we consider the temperature of the universe relative to the mass (which is the same terminology and thought we would use after EWSB).
    Where does this energy that is required to thermally produce the heavy neutrinos go, if they do not have mass yet.
    Can I think of it as potential? Or that the mass still specifies the energy needed, its just that the massive properties arent in play before EWSB?

    I'm not surprised we need a temp above the mass to thermally produce these particles, but I dont really understand what is happening or how I should picture the situation.
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