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I Neutrinos and Majorana mass

  1. Mar 2, 2017 #1
    So we are not yet sure exactly what mechanism accounts for the neutrino masses. One possible mechanism is the seesaw mechanism.

    Am I correct in thinking:

    Majorana mass terms are born from couplings between particles and antiparticles. This violates lepton number conservation and charge conservation. Therefore only neutral particles can have Majorana mass terms, i.e neutrinos. However that still does not account for lepton number. Is it therefore a requirement that neutrinos be there own antiparticle (i.e Majorana particles) for Majorana terms to exist so as to conserve lepton number?
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  3. Mar 4, 2017 #2


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    Lepton number is not conserved if neutrinos are Majorana particles.
  4. Mar 5, 2017 #3

    So, if Majorana mass terms violate lepton number conservation, why is it thought that it can be a method to explain the mass of a neutrino?
  5. Mar 5, 2017 #4


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    The logic is the other way round.

    Majorana masses are possible - consistent with observations so far and without theoretical issues.
    Majorana masses would lead to lepton number violation, but too small to be found by current measurements. Future measurements are more sensitive, they might find it.

    The best searches for Majorana masses are neutrinoless double beta decay searches. From neutrino oscillations, the most likely masses are <5 meV, 7-10 meV and 50 meV, although slightly higher masses have not been ruled out and there is still the option of an inverted order where one neutrino is light and two are relatively heavy (50-80 meV). Here is a recent review, figure 6 summarized the current experimental constraints from mixture measurements. Figure 17 shows the current upper limits of neutrinoless double beta decay searches. Figure 21 does some combinations.
    Last edited: Mar 5, 2017
  6. Mar 5, 2017 #5

    thank you! But I thought the Majorana masses didn't conserve lepton number? As it allows coupling of particle and antiparticle pairs??
  7. Mar 5, 2017 #6


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    Oops, I meant violation of course. Fixed.
  8. Mar 5, 2017 #7
    Oh right, perfect. Thank you very much!
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