In a video by Fermilab's YouTube channel "Can leptogenesis explain why there is something instead of nothing?", host Dr. Lincoln states four assumptions for the theory of leptogenesis. One of them is that neutrinos are Majorana particles - that is, they are their own antiparticles.

However, he also states that the point of the DUNE experiment is to test for differences in the behavior of neutrinos and antineutrinos, and he says detecting a difference would give evidence for leptogenesis.

How can these both be simultaneously true? If antineutrinos and neutrinos are the same, how could there be a difference in their morphing behaviors, as Dr. Lincoln says at around 13:00 in the video? What am I misunderstanding?

Video Link: https://youtu.be/PsqEcGMjEfo

  • $\begingroup$ From wiki: Antineutrinos are distinguished from the neutrinos by having opposite signs of lepton number and right-handed instead of left-handed chirality. The nature of the neutrinos is not settled—they may be either Dirac or Majorana fermions. So it's on-going debate about neutrinos being own antiparticles. Some opt for one, others - for another view. DUNE experiment should make situation more clear about neutrino. That's the point. $\endgroup$ Apr 9, 2020 at 11:23

1 Answer 1


One of them is that neutrinos are Majorana particles - that is, they are their own antiparticles.

In this publication of the Dune physics, one sees that the assumption of Dirac or Mayorana spinor for neutrinos makes a measurable difference in the predictions of the experiment , i.e in measured distributions for neutrinos and antineutrinos, not about their nature.

Complicated models are used for the prediction of the distributions:

If lepton-number is not imposed as a fundamental symmetry, Majorana masses for the RH neutrinos are also allowed and their magnitudes are unrelated to the scale of electroweak symmetry breaking. Once the Higgs gets a vacuum expectation value, both the Majorana and Dirac mass terms need to be included. If the RH-neutrino Majorana masses are much larger than the Dirac masses, this leads to small Majorana masses for the mostly-active neutrinos (those in the lepton-doublets) that manifest themselves via the Weinberg operator. This is the so-called seesaw mechanism and a strong suppression, without requiring very small Yukawa couplings, can be obtained if the RH neutrino masses are much heavier than the weak scale

They are not simple algebraic models.

The basic picture is the following. In the early universe, RH neutrinos were in thermal equilibrium for large temperatures. Once the temperature dropped below their mass, the bath does not have sufficient energy to keep them in equilibrium and they decouple, decaying into leptons and Higgs bosons. If there is CP violation, the decays of this channel and of the conjugated one can proceed with different rates, controlled by the CP-violating phases in the Yukawa couplings. This asymmetry is partially washed out by inverse processes and the remaining lepton asymmetry is converted into a baryon asymmetry later on by non-perturbative standard model (SM) effects.

There is no contradiction , because each Majorana neutrino will be an antiparticle of itself, but its existence will change the predictions for the distributions studied in the experiments.


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