It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. I noticed some article on massless Weyl fermions and it got me thinking. I'm wondering if there is any explanation for why bosons specifically gauge bosons can be massless photon and gluon but we don't see any fundamental massless fermions working from the most likely confirmed hypothesis that neutrinos are massive.
The unbroken part imposes its associated bosons gluons and photon to be massless to respect this symmetry. With fermions, there is no such constraint since their mass does not come from a gauge symmetry with our current knowledge, fermions masses are put by hand via add hoc yukawa couplings.
Therefore, the mass of the fermions is not predicted contrary to the masses of bosons. So, asking "why do we see no fundamental massless fermions? Answer: we don't know! I'm wondering if there is any explanation for why bosons specifically gauge bosons can be massless photon and gluon but we don't see any fundamental massless fermions.
It's because a fermion is a "body", and because "the mass of a body is a measure of its energy content". He talks about a body and an electron here. IMHO it's clear he thought of the electron as a body, and of radiation eg photons as energy.
So a photon is "not a body". It travels at the speed of light, it's never at rest, so it doesn't have a rest mass. Because "elementary" fermions such as electrons and positrons aren't truly "fundamental". You can create them in gamma-gamma pair production. Each is akin to a keV photon in a gedanken mirror-box of its own making.
In electron-positron annihilation you effectively open one box with another, whereupon each is a radiating body that loses mass. All of it. And then it's not there any more. The Higgs boson is a particle. It gets its mass like all other particles: by interacting with "swimming in" the Higgs field. But as you can imagine, the Higgs particle differs from all the other particles we know.
It can be thought of a dense spot in the Higgs field, which can travel like any other particle. Like a drop of water in water vapor.
In this sense one might call the Higgs particle the mediating particle of the proposed Higgs field, like you wrote. The Higgs field is the silent field that gives the mass. We cannot directly probe for it. But discovering the Higgs boson, the "mediator", would prove the existence of the Higgs field.
The Higgs particle, like many other elementary particles, is not a stable particle. Since it interacts with all kinds of other massive particles it can be created in collisions. The Higgs particle does not interact with massless particles, such as a photon or a gluon. Since these particles don't interact with the Higgs field, the Higgs boson also doesn't interact with them.
Once the Higgs particle has been created, it will eventually decay. Though the Higgs particle interacts with all massive particles it prefers to interact with the heaviest elementary particles we know, especially the top quark, which was discovered at Fermilab in We believe that it gains this albeit tiny mass due to the fact that it is influenced by the Higgs field. Without this influence, our Universe would have a completely different structure.
A massless electron would therefore be at infinity from the proton, not allowing atoms to form at all. In Nature, heavier particles tend to decay into lighter, more stables particles. In addition, the up and down quarks, that combine to form protons uud as well as neutrons udd , gain mass from their interaction with the Higgs field.
The bulk of the mass comes from the energy holding the quarks together, which is greater for the proton than the neutron.
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