Measuring the polarization content of gravitational waves with strongly lensed binary black hole mergers

Ignacio Magaña Hernandez

Submitted on 2 November 2022


Alternative theories of gravity predict up to six distinct polarization modes for gravitational waves. Strong gravitational lensing of gravitational waves allows us to probe the polarization content of these signals by effectively increasing the number of observations from the same astrophysical source. The lensing time delays due to the multiple observed lensed images combined with the rotation of the Earth allows for effective non-collocated interferometers to be defined with respect to the source location and hence probe the alternative polarization amplitudes with more observations. To measure these amplitudes, we jointly fit the image observations to a single gravitational wave signal model that takes into account the image magnifications, time delays, and polarization mode amplitudes. We show that for certain systems, we can make a measurement of the relative mode amplitudes for lensed events with two detectable images.


Comment: 8 pages, 6 figures

Subjects: General Relativity and Quantum Cosmology; Astrophysics - High Energy Astrophysical Phenomena


\label {fig:g_iota} We show the values for $g(\iota)$ as a function of the inclination angle $\iota$ for each of the six polarization modes. We note that for face-on systems ($\iota=0$), the vector and scalar modes will not be present in the GW strain data even if emitted. For edge-on systems ($\iota=\pi/2$), $\times$-mode and the vector-$x$ will not be detectable. The optimal inclination angle for which we maximize over the presence of all modes in the GW data corresponds to  $\iota_\text{opt} \approx 0.87$.