Neutrino Antineutrino annihilation possible?

[Claustral]

As far as I know, the anihilation of an electron by a positron is an electromagnetic process described by QED. Neutrinos, however, do not participate in the elektromagnetic interaction. Does that mean a Antineutrino will not anihilate a Neutrino of the same kind? Is there an interaction between Neutrino and Antineutrinofields and how does it look like? Maybe the weak interaction can also cause anihilation processes?

 

[Bill_K]

Yes, any particle can annihilate with its antiparticle. As you say, it would be caused by the weak interaction.

 

[vanhees71]

Sure, an electron neutrino and an electron antineutrino can be annihilated into an electron-positron pair. In the electroweak standard model the leading-order diagram is a W-boson exchange diagram.

 

[Dickfore]

No, it's a $Z^{0}$-boson exchange, since the total incoming (and outgoing) charge is zero.

 

[AdrianTheRock]

There is a key difference between low-energy electron/positron and neutrino/antineutrino pairs, though. The former can annihilate into pairs of photons because the latters' masses (zero) are less than the electrons'. In the case of anti/neutrinos, however, no such lighter particles exist. They can bump into one another and form a Z⁰, but the latter is off mass shell so has to decay almost immediately, and the only pair it has enough energy to create when decaying is another anti/neutrino pair. In effect, therefore, everyday anti/neutrinos such as ones from the cosmic background cannot annihilate.

 

[mfb]

It is true that low-energetic neutrinos cannot annihilate similar to electrons/positrons, but with a W-boson exchange there are allowed Feynman diagrams. I would assume that the cross-section is negligible, but not 0.

 

[Parlyne]

There is a key difference between low-energy electron/positron and neutrino/antineutrino pairs, though. The former can annihilate into pairs of photons because the latters' masses (zero) are less than the electrons'. In the case of anti/neutrinos, however, no such lighter particles exist. They can bump into one another and form a Z⁰, but the latter is off mass shell so has to decay almost immediately, and the only pair it has enough energy to create when decaying is another anti/neutrino pair. In effect, therefore, everyday anti/neutrinos such as ones from the cosmic background cannot annihilate.

Neutrinos have non-zero mass; and, as such can, at least in principle, annihilate to photons. The problem with this is that the annihilation involves a loop diagram with a highly off-shell W. This suppresses the cross-section significantly, making it essentially cosmologically irrelevant. But, it isn't correct to say that annihilation to photons is not allowed at all.

 

[AdrianTheRock]

Good point - thanks.

 

[Vanadium 50]

No, it's a $Z^{0}$-boson exchange, since the total incoming (and outgoing) charge is zero.

There is also t-channel W exchange. I don't know for sure, but suspect that it's the dominant process.

 

[Dickfore]

There is also t-channel W exchange. I don't know for sure, but suspect that it's the dominant process.

Ah, yes. The difference in cross-sections may be explained by the properties of the corresponding branching ratios for the decay of the corresponding weak vector boson.

 

[Claustral]

Thank you for your answers. You helped me a lot .