Adapting a semi-coherent method to directly detect dark photon dark matter interacting with gravitational-wave interferometers

We adapt a method, originally developed for continuous gravitational-wave searches, to directly detect dark photon dark matter. The method involves optimally choosing the analysis coherence time as a function of the frequency band analyzed, such that all of the signal's power will be confined to one frequency bin during the observation time. We describe the dark photon signal in detail, and show that due to its narrowband and continuous nature, methods used to search for isolated neutron stars can be powerful tools to search for dark photons. We derive a theoretical estimate of the sensitivity, and show that it is consistent with both the empirical sensitivity determined through software injections, and a cross-correlation method already developed. Additionally, we provide an end-to-end search design and estimate its computational cost, and show how follow-up techniques used in continuous wave searches are adapted to confirm or rule out dark photon dark matter candidates