Search for Subsolar-Mass Binaries in the First Half of Advanced LIGO's and Advanced Virgo's Third Observing Run

We report on a search for compact binary coalescences where at least one binary component has a mass between 0.2 M-circle dot and 1.0 M-circle dot in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend our previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio q >= 0.1. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of 0.14 yr(-1). This implies an upper limit on the merger rate of subsolar binaries in the range {[}220 - 24200] Gpc(-3) yr(-1), depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes in the mass range 0.2 M-circle dot < m(PBH) < 1.0 M-circle dot is f(PBH) equivalent to Omega(PBH)/Omega(DM) less than or similar to 6\%. This improves existing constraints on primordial black hole abundance by a factor of similar to 3. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at M-min = 1 M-circle dot, where f(DBH) equivalent to Omega(DBH)/Omega(DM) less than or similar to 0.003\%. These are the first constraints placed on dissipative dark models by subsolar-mass analyses.