Maximal gravitational wave signal from asteroid-mass primordial black hole mergers at resonant microwave cavities

Primordial black holes can be the entirety of the dark matter in a broad, approximately 5-orders-of-magnitude-wide mass range, the ``asteroid mass range,'' between ${10}^{\ensuremath{-}16}{M}_{\text{Sun}}$---where constraints originate from evaporation---and ${10}^{\ensuremath{-}11}{M}_{\text{Sun}}$---from microlensing. A direct detection in this mass range is very challenging with any known observational or experimental methods. Here we update the calculation of the sight distance for narrow-band detectors such as resonant microwave cavities and the resulting maximal event rate. We find that the largest detection rates are associated with binaries from nonmonochromatic mass functions in early-formed three-body systems. Even in the most optimistic setup, these events are anticipated to be extremely rare.