Constraints on millicharged dark matter and axionlike particles from timing of radio waves
We derive constraints on millicharged dark matter and axionlike particles using pulsar timing and fast radio burst observations. For dark matter particles of charge ee, the constraint from time of arrival (TOA) of waves is e/mmilli≲10-8  eV-1, for masses mmilli≳10-6  eV. For axionlike particles, the polarization of the signals from pulsars yields a bound in the axial coupling g/ma≲10-13  GeV-1/(10-22  eV), for ma≲10-19  eV. Both bounds scale as (ρ/ρdm)1/2 for fractions of the total dark matter energy density ρdm. We make a precise study of these bounds using TOA from several pulsars, FRB 121102, and polarization measurements of PSR J0437-4715. Our results rule out a new region of the parameter space for these dark matter models.