Leptogenesis and see-saw before EWSB

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Discussion Overview

The discussion revolves around leptogenesis models and their interactions involving heavy right-handed neutrinos and the Higgs field, particularly focusing on how these interactions can occur before electroweak symmetry breaking (EWSB). Participants explore the implications of Yukawa couplings and the nature of mass in relation to thermal production of heavy neutrinos.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that leptogenesis models create a lepton asymmetry through the decay of heavy right-handed neutrinos, questioning how Yukawa couplings can be relevant before EWSB.
  • Another participant argues that the coupling exists prior to EWSB, with the Higgs field acquiring a vacuum expectation value (vev) post-symmetry breaking, which facilitates the Dirac mass term and interaction structure.
  • A participant reflects on their misunderstanding regarding the timing of the Dirac mass term's existence, acknowledging that it is derived from the Yukawa couplings rather than being fundamental before EWSB.
  • A related question is raised about the thermal production of heavy neutrinos before EWSB, with a participant seeking clarification on the energy dynamics involved when neutrinos are massless, pondering whether this energy can be conceptualized as potential.

Areas of Agreement / Disagreement

Participants express differing views on the nature of mass and interactions before EWSB, with some clarifying the role of Yukawa couplings while others remain uncertain about the implications of mass in thermal production scenarios. The discussion does not reach a consensus.

Contextual Notes

Participants highlight the dependence on definitions of mass and energy in the context of EWSB, as well as the unresolved nature of how thermal production relates to massless particles.

Soph_the_Oaf
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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.

Thanks
 
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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.
 
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Hi

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.

Cheers
 
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 don't really understand what is happening or how I should picture the situation.
 

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