Photon splitting -- twenty years later

TL;DR

This paper reviews the history and recent developments in photon splitting research, including experimental observations at colliders and astrophysical evidence of related phenomena like vacuum birefringence.

Contribution

It provides a comprehensive overview of photon splitting experiments and observations over twenty years, highlighting recent collider and astrophysical findings.

Findings

ATLAS observed light-by-light scattering in heavy ion collisions

First astrophysical evidence of vacuum birefringence in neutron stars

Historical experimental challenges in detecting photon splitting

Abstract

In 1995, a team of physicists from the Budker Institute of Nuclear Physics in Novosibirsk was able to observe the splitting of a photon in the Coulomb field of an atomic nucleus for the first time, and reported the preliminary results of this experiment at two conferences. This was an extremely difficult experiment as the probability of the process is very small. It took another seven years to publish the final results. This story has been further developed recently. The ATLAS detector at the Large Hadron Collider observed in ultra-peripheral heavy ion collisions a process related to the photon splitting - light by light scattering. In addition, a team of Italian, Polish and British astrophysicists obtained the first observational evidence of the existence of vacuum birefringence in the magnetic field of an isolated neutron star - another physical phenomenon also related to the photon splitting. These new developments triggered this essay, written several years ago.