  We propose to use gravitational waves from extreme mass ratio inspirals
(EMRI), composed of a boson star and a supermassive black hole in the center of
galaxies, as a new method to search for boson stars. Gravitational waves from
EMRI have the advantage of being long-lasting within the frequency band of
future space-based interferometer gravitational wave detectors and can
accumulate large signal-to-noise ratio (SNR) for very sub-solar mass boson
stars. Compared to gravitational waves from boson star binaries, which fall
within the LIGO band, we find that much larger ranges of the mass and
compactness of boson stars, as well as the underlying particle physics
parameter space, can be probed by EMRI. We take tidal disruption of the boson
stars into account and distinguish those which dissolve before the
inner-most-stable-circular-orbit (ISCO) and those which dissolve after it. Due
to the large number of cycles recorded, EMRIs can lead to a very precise mass
determination of the boson star and distinguish it from standard astrophysical
compact objects in the event of a signal. Tidal effects in inspiralling binary
systems, as well as possible correlated electromagnetic signals, can also serve
as potential discriminants.
