Why do Majorana particles occur?

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    Majorana Particles
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Discussion Overview

The discussion centers on the nature of Majorana particles, particularly in relation to neutrinos and their potential to be their own antiparticles. Participants explore theoretical aspects of Majorana fermions, their characteristics, and the implications of current experimental searches.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants assert that Majorana particles are hypothesized fermions that are their own antiparticles, noting that no confirmed Majorana particles currently exist.
  • Others argue that while there are no known Majorana particles, neutrinos are suspected to be Majorana particles, contingent on the outcomes of neutrinoless double-beta decay experiments.
  • One participant suggests that none of the known neutrinos can be Majorana, proposing that only a yet-to-be-discovered sterile neutrino might possess a Majorana mass due to its zero quantum numbers.
  • Another participant counters that physical neutrinos could indeed be Majorana particles, as the conservation of certain charges is not applicable after electroweak symmetry breaking.
  • There is a claim that typical neutrino mass parameters in the Lagrangian are Majorana, and if no right-handed neutrinos exist, a Majorana mass is necessary.

Areas of Agreement / Disagreement

Participants express differing views on the possibility of known neutrinos being Majorana particles, with some asserting they cannot be, while others maintain that they might be under certain conditions. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight the dependence on theoretical frameworks and experimental results, particularly regarding the nature of neutrinos and the implications of electroweak symmetry breaking on their classification.

Positralino
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Why do Majorana particles occur?
For example, why is the antiparticle of photon itself?
 
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They don't. The photon is its own antiparticle but is not a Majorana particle. A Majorana particle is a hypothesized type of fermion that is its own antiparticle. There are no Majorana particles known.
 
A Majorana particle is a hypothesized type of fermion that is its own antiparticle. There are no Majorana particles known.

I think that's an overstatement. There are no particles we KNOW FOR SURE are majorana. However, we suspect neutrinos might be. The neutrinoless-double-beta-decay experiments will have to decide the question.
 
My understanding is that none of the known neutrinos can be Majorana. Only an as yet undiscovered sterile neutrino might have a Majorana mass, since all of its quantum numbers are zero. Isn't that right?
 
Bill_K said:
My understanding is that none of the known neutrinos can be Majorana. Only an as yet undiscovered sterile neutrino might have a Majorana mass, since all of its quantum numbers are zero. Isn't that right?

No. The physical neutrinos may, in fact, be Majorana particles. Certainly, the neutrino states that appear in the SM before EW symmetry breaking can't be Majorana, as they carry both SU(2)_L and U(1)_Y charges. However, after EWSB, those charges are no longer conserved and the neutrinos don't carry those that are. So, there's nothing to stop the physical neutrinos from being Majorana particles. It simply becomes a matter of whether the neutrino mass-generating mechanism allows it or not.
 
Bill_K said:
My understanding is that none of the known neutrinos can be Majorana. Only an as yet undiscovered sterile neutrino might have a Majorana mass, since all of its quantum numbers are zero. Isn't that right?

The known neutrinos don't carry any unbroken charges. The typical neutrino mass parameters added to the lagrangian are majorana. If there are no right-handed neutrinos, you have to have a majorana mass.
 

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