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Dear Dr B: Why Are Neutrinos Prove For Physics Beyond The Criterion Model?

Dear Chris,

The criterion model of particle physics contains 2 dissimilar types of particles. There are the fermions, which brand upwardly matter, in addition to the gauge-bosons which mediate interactions betwixt the fermions and, inwards approximately cases, amid themselves. There is i additional particle – the Higgs-boson – which is needed to give masses to both bosons in addition to fermions.

Neutrino number at the IceCube Observatory inwards Antarctica.
Image: IceCube Collaboration

The fermions come upwardly inwards left-handed in addition to right-handed versions which are mirror-images of each other. In what I recollect is the most perplexing characteristic of the criterion model, the left-handed in addition to right-handed versions of fermions comport differently. We state the fermions are “chiral.” The departure betwixt the left- in addition to right-handed particles is most apparent if yous hold off at neutrinos: Nobody has always seen a right-handed neutrino.

You could say, well, no problem, let’s simply become rid of the right-handed neutrinos. Who needs those anyway?

But it’s non that slow because nosotros accept known for xx years or in addition to so that neutrinos accept masses. We know this because nosotros encounter them mix or “oscillate” into each other, in addition to such an oscillation requires a non-vanishing mass-difference. This agency non all the neutrino-masses tin last zero.

Neutrino masses are a complication because the commons way to give masses to fermions is to span the left-handed version alongside the right-handed version in addition to alongside the Higgs. So what practice yous practice if yous accept no right-handed neutrinos in addition to yet neutrinos are massive?

The electrical flow condition is thence that either a) in that place are right-handed neutrinos but nosotros haven’t yet seen them, or b) neutrinos are dissimilar from the other fermions in addition to tin become masses inwards a dissimilar way. In either case, the criterion model is incomplete.

It is partly an number of terminology though. Some physicists state right-handed neutrinos are business office of the criterion model. In this instance they aren’t “beyond the criterion model” but instead their regain is pending.

I accept a personal fascination alongside neutrinos because I believe they’ll last fundamental to agreement the designing of particle-masses. This is because the right-handed neutrino is the solely particle inwards the criterion model that doesn’t send gauge-charges (or they are all zero, respectively). It seems to me that this should last the argue for it either beingness really heavy or non beingness in that place at all. But that’s speculation.

In whatsoever case, in that place many neutrino experiments shortly nether way to closer written report neutrino-oscillations in addition to equally good to hold off for “neutrinoless double-beta decay.” The relevance of the latter is that such a decay is possible solely if neutrinos are dissimilar from the other fermions of the criterion model, in addition to so that no additional particles are needed to practice neutrino masses.

So, no, particle physics isn’t dead in addition to over, it’s withal amount alongside discoveries waiting to happen!

Thanks for an interesting question.

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