Particle Probes with Superradiant Pulsars
Abstract
We demonstrate that rotational superradiance can be efficient in millisecond pulsars. Measurements from the two fastest known pulsars PSR J1748-2446ad and PSR B1937+21 can place bounds on bosons with masses below 10-11 eV. The bounds are maximally good at masses corresponding to the rotation rate of the star, where scalar interactions that mediate forces ~ 106 times weaker than gravity are ruled out, exceeding existing fifth force constraints by 3 orders of magnitude. For certain neutron star equations of state, these measurements would also constrain the QCD axion with masses between 5 10-13 and 3 10-12 eV. Despite the ability of most neutron star equations of state to support frequencies as high as ~ 1500 Hz, the observed absence of pulsars above ~ 700 Hz could be due to the existence of a new particle of mass ~ 10-11 eV with a Yukawa coupling to nucleons.