A Dirac fermion is made from the marriage of two Weyl fermionsĪ Dirac fermion is made from the marriage of two Weyl fermions. The second type of fermion, a Dirac fermion, is common in the Standard Model the electron is a Dirac fermion, as are its its cousins the tau and the muon, and all the quarks. The Standard Model fermions and their masses are shown below.įigure 2: A single Weyl fermion must have mass zero, and I will depict it, as it moves left to right, as a line indicating its path. Fermions are loners they refuse to do the same thing, and the “ Pauli exclusion principle” that plays a huge role in atomic physics, creating the famous shell structure of atoms, arises from the fact that electrons are fermions. Bosons are highly social and are happy to all do the same thing, as when huge numbers of photons are all locked in synch to make a laser.
What’s a fermion? All particles in our world are either fermions or bosons. Decades ago, in the original Standard Model, neutrinos were thought not to have any mass at all, and were “Weyl fermions.” Although I explained in my last post what these three types of fermions are, today I want go a little deeper, and provide you with a diagrammatic way of understanding the differences among them, as well as a more complete view of the workings of the “see-saw mechanism”, which may well be the cause of the neutrinos’ exceptionally small masses. In the second, they’d be “Majorana fermions”. In the first case, the neutrinos would be “Dirac fermions”, just like electrons and quarks. Earlier this week I explained how neutrinos can get their mass within the Standard Model of particle physics, either by engaging with the Higgs field once, the way the other particles do, or by engaging with it twice.
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