Uncovering the Mystery of Neutrino Interactions with Electromagnetic Force

[Upisoft]

While neutrinos have no electric charge they have magnetic moment and will interact with magnetic field causing precession of its spin.http://prl.aps.org/abstract/PRL/v45/i12/p963_1"

So if neutrinos can interact with virtual photons what makes it impossible to interact with real photons? What makes it impossible to annihilate in this way:
$$\nu + \bar{\nu} = \gamma + \gamma$$

 

[hamster143]

They don't couple to virtual photons directly. They go through a W/Z loop. And they do annihilate. They just happen to have an incredibly tiny cross section.

 

[Upisoft]

They don't couple to virtual photons directly. They go through a W/Z loop. And they do annihilate. They just happen to have an incredibly tiny cross section.

Meaning they will not annihilate to photons but to W/Z bosons? Did I get it correct?

 

[hamster143]

They can annihilate to photons, I think. There's a number of different possible outcomes. The issue is that, since they don't couple to photons directly, any annihilation process will involve one or more seriously off-mass-shell W/Z bosons, and that means a very low probability of annihilation.

 

[Vanadium 50]

, any annihilation process will involve one or more seriously off-mass-shell W/Z bosons

W's, not Z's, if you want photons in the final state. There are no photon-Z interactions in the SM.

 

[Upisoft]

W's, not Z's, if you want photons in the final state. There are no photon-Z interactions in the SM.

Ouch! What seemed to be improbable became almost impossible. At least for low energy neutrinos...

Thanks all for your answers.

 

[hamster143]

W's, not Z's, if you want photons in the final state. There are no photon-Z interactions in the SM.

can't you have something like a single Z in s channel and an electron loop at the end?

 

[Vanadium 50]

I don't think so. Landau-Yang theorem will block it.

 

[hamster143]

Good point. But you can have three photons.

Also, will it block the process completely or just suppress it by some power of neutrino mass? I'm not very clear on that. It seems that, since neutrinos are massive, the Z boson could have nonzero angular momentum.