Photon oscillations and cosmic background radiation

Abstract

The possible existence of a second species of photon which is uncoupled to known forms of matter is considered here. Explicit mass terms in the lagrangian can give rise to photon masses and to oscillations of photon identity, without sacrificing the ability of the gauge theory to be renormalized. Current upper limits on the photon mass are ∼6 × 10⁻¹⁶eV c⁻² (refs 1, 2). Photon oscillations corresponding to much smaller masses can significantly alter the spectral shape of the cosmic background radiation (CBR). Indeed, we show that the apparent discrepancy³ between theoretical and observed CBR spectra can be resolved in terms of photon oscillations, and a mass parameter of 5 × 10⁻¹⁸ eV c⁻².