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B Neutrino and New Physics

  1. Nov 27, 2017 #1
    Neutrino is one of the few things that belong to mainstream beyond standard model stuff. I was reading the October 2017 Scientific American article "Neutrino Puzzle" and I have some questions about the following:


    Once they know t he ordering of the neutrino masses, researchers can tackle the larger question of how neutrinos get their mass. Most particles, such as the protons and neutrons inside atoms, acquire mass by interacting with the Higgs field; this field, which pervades all of space, is associated with the Higgs boson found at the LHC. But the Higgs mechanism works only on particles that come in both right-handed and left-handed versions, a fundamental difference related to the orientation of their spin relative to their direction of motion. So far neutrinos have been seen only in left-handed form. If they got mass from the Higgs field, then right-handed neutrinos must also exist. But right-handed neutrinos have never been observed, which suggests that if they are real they do not interact at all with any other forces or particles in nature—and that prospect strikes some physicists as far-fetched. Furthermore, if the Higgs field did work on neutrinos, theorists would expect them to have similar masses to the other known particles. Yet neutrinos are inexplicably light. Whatever the mass states are, they are less than one hundred-thousandth of the mass of the already puny electron. “Very few people think it’s the Higgs mechanism that gives mass to the neutrinos,” says Fermilab’s director Nigel Lockyer. “There’s probably a completely different mechanism, and therefore there should be other particles associated with how that happens.”
    "One possibility that excites physicists is that neutrinos could be Majorana particles—particles that are their own antiparticles. (This is possible because neutrinos have no electric charge, and it is a difference in charge that distinguishes a particle from its antimatter counter
    part.) Theorists think Majorana particles have a way of getting mass without involving the Higgs field—perhaps by interacting with a new, undiscovered field. The mathematics behind this scenario also requires the existence of a very heavy set of neutrinos that has yet to be discovered; these particles would have up to a trillion times the mass of some of the heaviest known particles and would, in a sense, counterbalance the light neutrinos. For particle physicists, the prospect of discovering a new mass scale is enticing. “Historically we’ve always made progress by exploring nature at different scales,” de Gouvêa says. And if some new field gives mass to neutrinos, maybe it affects other particles as well. “If nature knows how to do it to neutrinos, where else does it do it?” Lockyer speculates. “Theorists are asking: Could dark matter be a Majorana mass?” "

    Some questions I'd like to ask:

    1. what are the proposals (any papers, references, etc?) for the completely different mechanism of how the neutrino may get mass in addition to Higg mechanism and relativistic energy/mass effects?

    2. All massless particles (or near massless particles) were supposed to travel at or near the speed of light. Is there any proposal or papers written where massless or near massless particles, instead of travelling straight are in some standing wave form (like circling in a loop), and how do they do that?

    Thank you!
  2. jcsd
  3. Nov 28, 2017 #2


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    This is not very accurate. The neutrino Dirac mass would be expected to be similar to the mass of the other fermions. However, being a Standard Model singlet, the right handed neutrino would generally allow for an additional Majorana mass term and there is no a priori way of forbidding it. There would be no a priori handle on the size of this mass term as it would be unrelated to anything we know. It is popular to theorise that this Majorana mass term is significantly larger than the Dirac mass. If that is the case it would naturally suppress the masses of the Standard Model neutrinos and thereby actually explain why neutrino masses are so small. This is known as the (type-I) seesaw mechanism.

    Truth with modification. The Higgs mechanism is part of the seesaw mechanism and the Higgs is therefore also involved in the seesaw.

    These new particles are exactly the same right-handed neutrinos he talked about before, just with an additional Majorana mass term. The Higgs field is most definitely involved in allowing the heavy mass to suppress the Standard Model neutrino masses.

    Apart from the type-I seesaw mechanism (you should find this in any review of neutrino physics), which involves right-handed neutrinos, there are the type-II and type-III seesaw mechanisms, which involve adding an additional scalar SU(2) triplet and an additional fermion SU(2) triplet, respectively.

    Not that I am aware of.
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