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 ϵe, the constraint from time of arrival (TOA) of waves is ϵ/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.