What is the velocity of neutrinos, and do their interact with the HIggs field?

1. Apr 29, 2007

ensabah6

If Neutrinos have mass, What is the velocity of neutrinos,
can they "slow down" due to gravity, and do their acquire their mass from interactions with the HIggs field?

2. Apr 29, 2007

Parlyne

For neutrinos of reasonable energy, the velocity will be extremely close to the speed of light; but, it will depend on how much energy they have, just as with any other particle.

It is not currently know exactly how neutrinos acquire mass. There are quite a few models out there. The simplest mechanism is the same Higgs mechanism through which all the other particles acquire mass. However, this requires two things. First, there must be right-handed neutrinos, which no one has ever seen. And, the neutrino coupling to the Higgs field must be ridiculously small (something like 8 orders of magnitude smaller than the electron Higgs coupling). This second requirement, in particular, has led people to look for other ways to make the neutrino mass small more naturally. However, every such method requires adding new physics that there is no experimental evidence for. So, suffice it to say, this is still an open question.

3. Apr 29, 2007

ensabah6

So could neutrinos with really low kinetic energy be cold dark matter candidate? Presumably gravity can slow them down.

Is the mass of neutrinos rest mass?

4. Apr 29, 2007

Parlyne

No, I'm afraid not. They just don't have enough mass to be able to form the halos of galaxies early in the universe's evolution. They would have to have had far less kinetic energy than we know them to have had.

Yes. When people talk about the mass of any fundamental particle, what they mean is rest mass (or, equivalently, what you get by calculating $$\frac{\sqrt{E^2 - p^2c^2}}{c^2}$$). In the case of neutrinos, though, this is so small that we can't measure it directly. In fact, so far all the neutrino mass measurements we have are actually measurements in the differences between the squares of the masses of different neutrino species. We don't actually know the overall scale of the masses.