Real-Time Measurement of the Population Densities in Gd Atomic Vapor Using Diode Laser Absorption Spectroscopy at 394.554 nm

Abstract

We derive new constraints on the coupling of heavy pseudoscalar (axion-like) particles to photons, based on the gamma ray flux expected from the decay of these particles into photons. After being produced in the supernova core, these heavy axion-like particles would escape and a fraction of them would decay into photons before reaching the Earth. We have calculated the expected flux on Earth of these photons from the supernovae SN 1987A and Cassiopeia A and compared our results to data from the Fermi Large Area Telescope. This analysis provides strong constraints on the parameter space for axion-like particles. For a particle mass of 100 MeV, we find that the Peccei-Quinn constant, f a , must be greater than about 10 15 GeV. Alternatively, for f a = 10 12 GeV, we exclude the mass region between approximately 100 eV and 1 GeV.