Evolution of supermassive black hole binaries and tidal disruption rates
  in nonspherical galactic nuclei
  Binary supermassive black holes (SMBH) are expected to form naturally during
galaxy mergers. After the dynamical friction phase, when the two SMBHs become
gravitationally bound to each other, and a brief stage of initial rapid
hardening, the orbit gradually continues to shrink due to three-body
interactions with stars that enter the loss cone of the binary. Using the
stellar-dynamical Monte Carlo code Raga, we explore the co-evolution of the
binary SMBH and the nuclear star cluster in this slow stage, for various
combinations of parameters (geometry of the star cluster, primary/secondary
SMBH mass, initial eccentricity, inclusion of stellar captures/tidal
disruptions). We compare the rates of stellar captures in galactic nuclei
containing a binary to those of galaxies with a single SMBH. At early times,
the rates are substantially higher in the case of a binary SMBH, but
subsequently they drop to lower levels. Only in triaxial systems both the
binary hardening rates and the capture rates remain sufficiently high during
the entire evolution. We find that the hardening rate is not influenced by star
captures, nor does it depend on eccentricity; however, it is higher when the
difference between the black hole masses is greater. We confirm that the
eccentricity of the binary tends to grow, which may significantly shorten the
coalescence time due to earlier onset of gravitational-wave emission. We also
explore the properties of the orbits entering the loss cone, and demonstrate
that it remains partially full throughout the evolution in the triaxial case,
but significantly depleted in the axisymmetric case. Finally, we study the
distribution of ejected hypervelocity stars and the corresponding mass deficits
in the central parts of the galaxies hosting a binary, and argue that the
missing mass is difficult to quantify observationally.
