Abstract
Pseudoscalar particles, with almost zero mass and very weakcoupling to the visible matter, are hypothesized in many extensions of thestandard model of particle physics. They mix with photons in presence abackground magnetic field leading to interesting astrophysical andcosmological signatures. This mixing depends on the medium properties, themomentum of the photon and the background magnetic field. Here we give ageneral treatment of pseudoscalar-photon oscillations in a backgroundmagnetic field, taking the Faraday term into account. We predict resultsvalid in all regimes, under the assumption that the frequency of the waveis much higher than the plasma frequency and the gyration frequency of themedium. At sufficiently high frequencies, the Faraday effect is negligibleand we reproduce the standard pseudoscalar-photon mixing phenomenon.However at low frequencies, where Faraday effect is important, the mixingformulae are considerably modified. We calculate the stokes parameters toillustrate this. We also explicitly compute the contribution due to thelongitudinal mode of the photon and show that it is negligible for most ofthe astrophysical application.
