SN 1987A Gamma-Ray Limits on the Conversion of Pseudoscalars

Abstract

Pseudoscalar particles $\varphi$ usually couple electromagnetically by an interaction of the form $\text{frc}14g\varphi F\tilde{F}$, allowing them to convert to photons in the presence of magnetic fields. Notably, new low-mass pseudoscalars emitted from supernova (SN) 1987A would have been converted to $\gamma$-rays in the intervening magnetic field of the galaxy. Therefore, measurements by the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS) can limit the inverse coupling constant to $g^{-1}>1\times 10^{11}\mathrm{GeV}$, assuming the pseudoscalar is massless. This is an improvement over other astrophysical limits of a factor of about 2.5.

Comments: 10 pages, plus 4 PostScript files (included)