Detector configuration of DECIGO/BBO and identification of cosmological
  neutron-star binaries
  The primary target for the planned space-borne gravitational wave
interferometers DECIGO/BBO is a primordial gravitational wave background
(PGWB). However there exist astrophysical foregrounds and among them,
gravitational waves from neutron star (NS) binaries are the solid and strong
component that must be identified and subtracted. In this paper, we discuss the
geometry of detector configurations preferable for identifying the NS/NS binary
signals. As a first step, we analytically estimate the minimum signal-to-noise
ratios (SNRs) of the binaries for several static detector configurations that
are characterized by adjustable geometrical parameters, and determine the
optimal values for these parameters. Next we perform numerical simulations to
take into account the effect of detector motions, and find reasonable
agreements with the analytical results. We show that, with the standard network
formed by 4 units of triangle detectors, the proposed BBO sensitivity would be
sufficient in receiving gravitational waves from all the NS/NS binaries at
$z\le 5$ with SNRs higher than 25. We also discuss the minimum sensitivity of
DECIGO required for the foreground identification.
