Constraining gravitational-wave polarizations with Taiji

Space-based gravitational-wave detectors consist of a triangle of three spacecraft, which makes it possible to detect polarization modes of gravitational waves due to the motion of the detectors in space. In this paper we explore the ability of Taiji to detect the polarization modes in the parametrized post-Einsteinian framework. Assuming massive black hole binaries with the total mass of $M=4\times {10}^5{M}_{\odot }$ at redshift of $z=1$, we find that Taiji can measure the dipole and quadruple emission ($\mathrm{\Delta }{\alpha }_D\mathrm{/}{\alpha }_D$ and $\mathrm{\Delta }{\alpha }_Q\mathrm{/}{\alpha }_Q$) with the accuracy of up to $\sim 0.04\mathrm{\%}$, with the fiducial value of ${\alpha }_D=0.001$, the scalar transverse and longitudinal modes ($\mathrm{\Delta }{\alpha }_B$ and $\mathrm{\Delta }{\alpha }_L$) up to $\sim 0.01$, and the vector modes ($\mathrm{\Delta }{\alpha }_V$) up to $\sim 0.0005$.