Can't the same question be asked of any "force carrier" particle? Photons are (massless) carriers of the EM force, and are emitted when charge-carrying particle/antiparticle pairs annihilate. Gluons are the (also massless) carriers of the strong force, and are emitted when color-carrying particle/antiparticle pairs annihilate. So perhaps it is generally true that these massless carrier particles have no antiparticles? I guess that may be a bit ambiguous, since QCD requires 8 distinct kinds of gluons, and I guess none of them have ever been observed directly, but I have not read that they are generally organized into gluon-antigluon pairs.

Anyhow, what would be emitted in the annihilation of a putative photon-antiphoton pair? I mean, energy and momentum have to be conserved, right?

EDIT: so, to further qualify my own question, I know electron-positron pair production is possible if the photon energy is high enough ... I am trying to understand the general situation that would be valid at all photon energies. Particle physicists remind me of that crazy race in Star Trek that could only talk to Captain Picard in metaphors.

We're hunting for the quantum duck! The Jacobs Duck swims in a pond of ice cream, except it doesn't just swim, it vibrates directionally by simultaneously existing and not existing. The Jacobs Duck has never been spotted, only inferred by theorietical mid-70's work that discovered the eight kinds of subatomic spoons: north, south, east, southeast, here, there, out, and spork. Seven spoons make a spoonbag; eight make a Grand Duchy. The spoons coexist spacially - but not temporally - in the ice cream pond, which corresponds to a field that stretches from the sun to your sock drawer, which sits in a state of perpetual existential crisis. We have, however, discovered traces of anti-ducks, which can be seen scattered across a Heintzman windshield when driven through a deep mine on a trolley, and indicate the possibility of a hidden realm that really doesn't make much sense at all.
posted by bicyclefish at 4:56 PM on February 16 [42 favorites]