Probing gravitational wave polarizations with Advanced LIGO, Advanced Virgo and KAGRA

Understand

Assuming that, for a given source of gravitational waves (GWs), we know its sky position, as is the case of GW events with an electromagnetic counterpart such as GW170817, we discuss a null stream method to probe GW polarizations including spin-0 (scalar) GW modes and spin-1 (vector) modes, especially with an expected network of Advanced LIGO, Advanced Virgo and KAGRA.

• For two independent null streams for four non-co-aligned GW detectors, we study a location on the sky, exactly at which the spin-0 modes of GWs vanish in any null stream for the GW detector network, though the strain output at a detector may contain the spin-0 modes.
• Our numerical calculations show that there exist seventy sky positions that satisfy this condition of killing the spin-0 modes in the null streams.
• If a GW source with an electromagnetic counterpart is found in one of the seventy sky positions, the spin-1 modes will be testable separately from the spin-0 modes by the null stream method.