Pulsars as Probes of the Axion and Dilaton Electromagnetic Couplings

We use public timing data from 2549 pulsars to probe the electromagnetic couplings of the axion and dilaton fields. The strong magnetic fields and rapid rotation of pulsars allows the region around the pulsar to have a nonvanishing E · B, which enables a conversion of rotational energy into axions or dilatons that is proportional to the square of their coupling to electromagnetic fields. By using the pulsar spin-down power Ė as the upper limit of the power radiated into either field, we place upper limits on the relevant couplings. We find limits for the axion-photon coupling g_aγγ of 10^-10 GeV^-1 for axion masses <~10^-13 eV. Meanwhile, the limits on the equivalent electromagnetic coupling for the dilaton, κ, are ~2 orders of magnitude stronger than those on the axion. This limit on κ could potentially be used to constrain varying-fine structure constant (α) models, which is the current phase of the project.