Probing nontensorial gravitational waves with a next-generation ground-based detector network

In General Relativity, there are only two polarizations for gravitational waves. However, up to six polarizations are possible in a generic metric theory of gravity. Therefore, measuring the polarization content of gravitational waves provides an efficient way to test theories of gravity. We analyze the sensitivity of a next-generation ground-based detector network to nontensorial polarizations. We present our method to localize GW signals in the time-frequency domain and construct the model-independent null stream for events with known sky locations. We obtain results based on simulations of binary neutron star mergers in a six-detector network. For a single event at a luminosity distance $D_L=100\mathrm{M}\mathrm{p}\mathrm{c}$, at $5\sigma$ confidence, the smallest amplitude for detection of scalar and vector modes relative to tensor modes are respectively $A_s=0.045$ and $A_v=0.014$. For multiple events in an averaged observing run of 10 years, the detection limits at $5\sigma$ confidence are $A_s=0.05$ and $A_v=0.02$. If we are fortunate, a few strong events might significantly improve the limits.