How do intense magnetic fields cause photons to split or merge?

[RJ Emery]

Accompanying the article "Magnetars," by Kouveliotou, et al, Scientific American, February, 2003, is a graphic labeled "Extreme Magnetism" which shows four ways in which "Magnetar fields wreak havoc with radiation and matter."

One of these ways is spontaneous (my word) Photon Splitting, described as "In a related effect, x-rays freely split in two or merge together. This process is important in fields stronger than 10^14 gauss."

I have trouble visualizing or understanding this process by which a photon can split or merge with another photon which doesn't involve some other particle (e.g., an electron). If someone could elaborate in layman terms, it would be appreciated.

FWIW, the three other ways listed are Vacuum Birefringence, Scattering Suppression, and Distortion of Atoms.

 

[mgb_phys]

Cool - I had never heard of that before.
I think the paper says that the photon splits into a electron-positron pair and because these are in a strng magnetic field they emit photons before recombining.

 

[RJ Emery]

Cool - I had never heard of that before.
I think the paper says that the photon splits into a electron-positron pair and because these are in a strng magnetic field they emit photons before recombining.

What paper is that? Certainly not the article I cited. All it says is:

A separate estimate of the field had been given in 1992 by Bohdan Paczynski of Princeton. He noted that x-rays can slip through a cloud of electrons more easily if the charged particles are immersed in a very intense magnetic field. For the x-rays during the burst to have been so bright, the magnetic field must have been stronger than 10^14 gauss.

What makes the theory so tricky is that the fields are stronger than the quantum electrodynamic threshold of 4 × 10^13 gauss. In such strong fields, bizarre things happen. X-ray photons readily split in two or merge together. The vacuum itself is polarized, becoming strongly birefringent, like a calcite crystal. Atoms are deformed into long cylinders thinner than the quantum-relativistic wavelength of an electron.

It provides the observation of what could happen, but does not explain how, at least to my rudimentary level of understanding.