Detecting massive vector fields with extreme-mass-ratio inspirals

The future space-borne gravitational wave detector, Laser Interferometer Space Antenna (LISA), has the potential of detecting fundamental fields, such as the charge and mass of the ultralight scalar field. In this paper, we study the effect of lighter vector fields on the gravitational waveforms from the extreme-mass-ratio inspirals (EMRI) system, consisting of a stellar-mass object and the massive black hole in the Einstein-Proca theory of a massive vector field coupling to gravity. Using the perturbation theory, we compute the energy fluxes, including the contributions of the Proca field and the gravitational field, then obtain the adiabatic inspiraling orbits and corresponding waveforms. Our results demonstrate that the vector charge and mass carried by the secondary body lead to detectable effects on the EMRI waveform, and LISA has the potential to measure the mass of the Proca field with greater precision.