EFFECTS OF A NAMBU-GOLDSTONE BOSON ON THE POLARIZATION OF RADIO GALAXIES AND THE COSMIC MICROWAVE BACKGROUND

A coupling g-phi-E.B to a pseudoscalar field phi affects the polarization properties of electromagnetic waves as they propagate through background fields. We analyse the bounds imposed on g from astronomical polarization measurements. If phi is the Nambu-Goldstone boson field of a global symmetry spontaneously broken at an energy scale nu, then g = N-alpha/pi-nu with N a model-dependent numerical coefficient. For an exactly massless Nambu-Goldstone boson, we show that N greater than or similar to the observed correlation between polarization properties and shape of distant radio galaxies and quasars, unless there was inflation after the breakdown of the global symmetry. We also show that propagation through intervening magnetic fields induces a small degree of linear polarization in the cosmic microwave background.