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6

Short answer: mostly no. Slightly longer answer: the interaction of neutrinos with the molecules of your body take several forms, but they all come down to ionizing dose. However, there are many larger sources of ionizing dose in your like. Things like the Potasium-40 in the food you eat, radon and Carbon-14 in the air you breath, cosmic rays, and on and ...

3

We need to distinguish between the concept of Dark Matter and the potential candidates that fill it's role. Dark matter, as originally posited, was just non-luminous matter that could be inferred only through gravity. As time went on, additional research shed more light on what dark matter was. Both the growth of large scale structure of the universe and ...

2

pfnuesel's answer is absolutely correct and very satisfying to understand, and you should read it before this one. There is, however, a route which would permit $\pi\to e+\nu$ even if the electron were massless. The conserved quantity which suppresses that decay is not spin, but total angular momentum. There exists an electron+neutrino wavefunction with ...

21

Since the spin of the charged $\pi$ is $0$, the spins of the daughter particles need to add up to $0$ as well, i.e., their spins need to be anti-parallel. That's nothing else than the conservation of angular momentum. Assuming the anti-neutrino to be massless, it is always right-handed. Right-handed means that the momentum vector and the spin vector are ...

1

This is mostly to make an explicit connection with natural units - the unit system in which $\hbar$ and $c$ are both set to 1, which is the natural set of units for relativistic quantum theory. Because you've adimensionalized two units and you had three physical dimensions to start with (mass, length and time), natural units retain a single dimensional ...

2

I am going to take a stab at answering my own questions with what I have been able to find on the subject. (Still very sparse.) 1) In this model the SU(2) confinement occurs at much higher energies than SU(3) confinement, so that the weak-partons confine first (giving us quarks and leptons) and then quarks confine into hadrons second. This explains why ...

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