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Abstract

Every signal propagating through the universe is diffracted by the
gravitational fields of intervening objects, aka gravitational lenses.
Diffraction is most efficient when caused by compact lenses, which invariably
produce additional images of a source. The signals associated with additional
images are generically faint, but their collective effect may be detectable
with coherent sources, such as gravitational waves (GWs), where both amplitude
and phase are measured. Here, I describe lens stochastic diffraction (LSD):
Poisson-distributed fluctuations after GW events caused by compact lenses. The
amplitude and temporal distribution of these signals encode crucial information
about the mass and abundance of compact lenses. Through the collective
stochastic signal, LSD offers an order-of-magnitude improvement over single
lens analysis for objects with mass $\gtrsim 10^3 M_\odot$. This gain can
improve limits on compact dark-matter halos and allows next-generation
instruments to detect supermassive black holes, given the abundance inferred
from quasar luminosity studies.