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Why is the Majorana mass of a neutrino so big compared to the

  1. Jun 8, 2008 #1
    [Moderator's note: Quoted-printable stuff NOT corrected. Sometimes I
    correct small errors, but a) there are several here and b) it is not
    obvious what the meaning should be. Please submit only 100% 7-bit ASCII
    plain-text posts. Even if YOU can read something fancier, many readers
    can't. -P.H.]

    I read the abstract of Prof. Vafa's recent paper on string
    phenomenology. (arXiv:0806.0102)
    But, I don't really understand the following part:

    "This effect can simultaneously generate a viably small =A5=EC term as well
    as an acceptable Dirac neutrino mass on the order of 0.5=A1=BF 10^(-2=A1=BE0=
    ..5)
    eV. In another scenario, we find a modified seesaw mechanism which
    predicts
    that the light neutrinos have masses in the expected range while the
    Majorana mass term for the heavy neutrinos is =A1=AD 3=A1=BF10^(12=A1=BE1.5)=
    GeV."

    So, it seems that the Majorana mass of neutrino is much much bigger
    than the Dirac mass of neutrino.
    Why is it so? As far as I know, the mass of neutrino is very small.
    But, how can this light neutrinos have so big Majorana mass? Or,
    rather, as stated in the excerpt, is there something called "the heavy
    neutrinos" different from the light neutrinos which I am familiar
    with?

    Or, rather, even though it's unlikely, is Prof. Vafa suggesting that
    "another scenario" of his is incorrect, since it predicts a big
    Majorana mass?

    I am confused,

    Youngsub.
     
  2. jcsd
  3. Jun 10, 2008 #2
    yy...@fas.harvard.edu wrote:
    > Or, rather, even though it's unlikely, is Prof. Vafa suggesting that
    > "another scenario" of his is incorrect, since it predicts a big
    > Majorana mass?


    It has nothing per se to do with string theory, but is a somewhat
    standard part of folklore in neutrino physics. The *left* neutrino and
    *right* anti-neutrino have small masses. The *right* neutrino and
    *left* anti-neutrino, on the other hand, are usually stipulated to
    have large masses. This is part of the See Saw mechanism and is used
    to explain why the left neutrino (and right anti-neutrino) have such
    small masses.
     
  4. Jun 11, 2008 #3
    On Jun 7, 8:49 pm, yy...@fas.harvard.edu wrote:
    > So, it seems that the Majorana mass of neutrino is much much bigger
    > than the Dirac mass of neutrino.
    > Why is it so? > Youngsub.



    Stimulated by Rock B's explanation, I've just learned from the
    references in Wikipedia that explain this whole matter
    straightforwardly:

    http://en.wikipedia.org/wiki/Neutrino

    http://en.wikipedia.org/wiki/Sterile_neutrino

    http://en.wikipedia.org/wiki/Seesaw_mechanism

    Regards - P
     
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