# Photon+photon -> neutrino + antineutrino ?

1. Jul 12, 2011

### PAllen

High energy gamma rays in a region of reasonable matter density quickly produce a plethora of lower energy photons by a series of interactions, stopping when you have photons too low in energy to produce positron/electron pairs.

My question concerns the likelihood of the titular reaction (which would effectively carry the energy of photons away from a high density region). I found some very old papers discussing its likelihood in models predating the intermediate vector boson model of weak interactions. Can someone comment on the likelihood and point me at any not too advanced discussion in the context of the electro-weak theory?

[Edit: I also found good, modern, discussion of photon+<charged particle or nucleus> producing neutrino pairs. But the above, presumably less significant interaction, was not covered]

Last edited: Jul 12, 2011
2. Jul 12, 2011

Staff Emeritus
It's going to be ridiculously small. A ballpark estimate would be the rate for light-by-light scattering, times (E_gamma/m_W)^4.

3. Jul 12, 2011

### bcrowell

Staff Emeritus
Is there some astrophysical context where you would get an insanely high density of high-energy gammas, but no matter? Evaporation of a microscopic black hole?

4. Jul 12, 2011

### PAllen

Ok, this is the take away point. Independent of details, and despite the near vanishing mass of neutrinos, this is going to be extremely rare because it has to be mediated by a virtual vector boson whose mass makes this unlikely. At all energy regimes, other results will be many orders of magnitude more likely. But this is not a prohibited interaction, just very unlikely.