Gravitational Wave Background Search by Correlating Multiple Triangular
  Detectors in the mHz Band
  With the recent strong developments of TianQin and Taiji, we now have an
increasing chance to make a correlation analysis in the mHz band by operating
them together with LISA. Assuming two LISA-like triangular detectors at general
geometrical configurations, we develop a simple formulation to evaluate the
network sensitivity to an isotropic gravitational wave background. In our
formulation, we fully use the symmetry of data channels within each triangular
detector and provide tractable expressions without directly employing
cumbersome detector tensors. We concretely evaluate the expected network
sensitivities for various potential detector combinations, including the
LISA-TianQin pair.
