Photon Splitting and Pair Conversion in Strong Magnetic Fields

TL;DR

This paper explores quantum electrodynamics phenomena like photon splitting and pair creation in neutron star magnetic fields, discussing their physical mechanisms, astrophysical signatures, and potential for experimental verification with upcoming gamma-ray observations.

Contribution

It provides a detailed analysis of photon splitting and pair conversion processes in strong magnetic fields, highlighting their astrophysical implications and observational signatures in neutron star environments.

Findings

Photon splitting can occur without an energy threshold.

Pair creation is exponentially suppressed in weak fields.

Spectral turnovers in pulsars can diagnose these processes.

Abstract

The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST mission, to be launched by NASA in 2008. Suppression of pair creation by photon splitting and its implications for pulsars is also discussed.