Determination of pseudo-Goldstone-boson–photon coupling by the differential time delay of pulsar signals

Pseudo Goldstone bosons couple with photons through a P and T violating interaction of the form L=g_αγγ{α}FF ̃ \~{}{}. Strong magnetic fields in rotating compact stars induce a nonzero E{·}B outside the stellar surface which acts as a source for the pseudoscalar field. Pulsar signals propagating through this pseudoscalar ``hair'' suffer a differential time lag between the left and the right circularly polarized modes because of the P and T violating pseudoscalar-boson--photon interaction. Determination of this time lag up to a microsecond accuracy can lead to a measurement of (or rule out) pseudo-Goldstone-boson--photon coupling up to g_aγγ{≤}2.0×{}10^-11 GeV^-1.