Quote:
Originally Posted by sjastro
There are four properties that differentiate matter from it's mirror image (antimatter).
(1) Charge
(2) Magnetic moment
(3) Parity
(4) Helicity or handedness.
Charge is obvious, parity and helicity relate to the mathematical symmetries of particles and antiparticles. So for example if a particles intrinsic spin and linear momentum are in the same direction then the particle has a positive helicity where as the corresponding anti particle will have the instrinsic spin and linear momentum in opposite directions (negative helicity). All neutrinos are left handed, all antineutrinos are right handed.
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Just to clarify this point a little.. You can have left and right handed electrons, just as you can have left and right handed positrons.
Neutrinos are an altogether different matter since it is no known if they are Dirac fermions (like electrons) or Majorana fermions. If they are Majorana fermions they would be their own anti-particles - like photons. The standard model of particle physics assumes neutrinos to be Dirac fermions.
Since the Weak force only interacts with left handed particles and right handed antiparticles and so if neutrinos are Majorana fermions then neutrinoless double beta decay would be possible.
This is all important because we know neutrinos have mass, but we dont know how to theoretically express the origin of their mass. Trying to use the Higgs mechanism (as is used to give all other particles mass) breaks gauge invariance - something held in very high regard amongst physicists. There are other mechanisms for explaining neutrino masses such as the see-saw mechanism, but it depends on the particulars of how many neutrinos there are and whether they are Majorana or Dirac fermions. A plus side to the see-saw mechanism is that it requires a heavy sterile neutrino which is a candidate for dark matter.
Hope I havent rambled too much..