Science with the TianQin Observatory: Preliminary Results on Stochastic
  Gravitational-Wave Background
  In this work, we study the prospect of detecting the stochastic
gravitational-wave background with the TianQin Observatory. We consider sources
of both astrophysical-origin and cosmological-origin, including stellar-mass
binary black holes, binary neutron stars, Galactic white dwarves, inflation,
first-order phase transitions, and cosmic defects. For the detector
configurations, we consider TianQin, TianQin I+II, and TianQin + LISA. We study
the detectability of stochastic gravitational-wave backgrounds with both the
cross correlation and null channel methods, and present the corresponding
power-law integrated sensitivity curves. We introduce the definition of the
"joint foreground" with a network of detectors. With the joint foreground, the
number of resolved double white dwarves in the Galaxy will be increased by
5$-$22\% compared with a simple combination of individual detectors. The
astrophysical background is expected to be detectable with a signal-to-noise
ratio of 100 after 5 years of operation and dominated by the extragalactic
double white dwarves. On the other hand, due to the uncertain nature of
underlying models, we can only estimate the detection capability of the
cosmological background for specific cases.
