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Do neutrinos and antineutrinos annihilate?

by pierce15
Tags: annihilate, antineutrinos, neutrinos
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phinds
#19
Jun12-14, 04:03 PM
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Quote Quote by ChrisVer View Post
Of course, if the OP checks the other thread I posted, he'll find that people there said the process of neutrino-antineutrino annihilation is not yet observed, because it's very small... neutrinos interact hardly with matter, just imagine expecting two of them to interact with each other hehehe.
Yes, that was the point of post #2
Bill_K
#20
Jun12-14, 04:20 PM
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Quote Quote by ChrisVer View Post
neutrinos interact hardly with matter, just imagine expecting two of them to interact with each other hehehe.
In some circumstances it can be important. This paper says:
ABSTRACT: Neutrino-antineutrino annihilation into electrons and positrons can
deposit more than 10 to the 51st ergs above the neutrino-sphere of a
type II supernova.
Bill_K
#21
Jun12-14, 04:43 PM
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Quote Quote by ChrisVer View Post
neutrinos interact hardly with matter, just imagine expecting two of them to interact with each other hehehe.
Granted, it's a weak interaction, but there are several points to note... first of all the cross-section of the lowest order Feynman diagram for neutrino scattering is G2s - it grows rapidly with energy. The traditional "light-year of lead" remark is, I'm afraid, popsci woo. It pertains to low energy neutrinos, and does not take the energy dependence into account.

Secondly, thanks to the universality of the weak interactions, the scattering cross-section's about the same no matter what the neutrino hits - quark, electron, what-have-you.

Thirdly, the way we succeed in detecting neutrino interactions in the lab is to have a very large detector with a very large number of target particles. Neutrinos, of course,can't be focused. Their interactions become important in natural situations where the neutrino density is high.
Orodruin
#22
Jun12-14, 04:52 PM
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To underline the fact of energy dependence of the cross section, the Earth is completely opaque to ultra-high energy neutrinos (say 1 PeV) such as the ones recently detected by IceCube.

When trying to detect dark matter annihilations in the Sun, the effect (absorbtion and tau regeneration) becomes relevant at even lower energies. Still, solar neutrinos from the usual solar fusion have far too low energy for scattering to matter although coherent forward scattering plays a key role in the flavor transitions of such neutrinos.


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