Does GW170814 rule out non-tensorial gravitational wave polarization?

To determine the polarization character of gravitational waves, we use strain data from the GW170814 binary black hole coalescence event detected by the three LIGO-Virgo observatories, extracting the gravitational wave (GW) strain signal amplitude ratios and phase differences directly from those data. Employing a geometric approach that links those ratios and phase differences to the GW polarization properties, we find that there is a range of source sky locations, close to the LIGO-Virgo 90% credible range of GW170814 source locations, for which vector polarization is consistent with the observed amplitude ratios and phase differences. A Bayesian inference analysis indicates that the GW170814 data cannot rule out vector polarization for gravitational waves. We suggest a plausible explanation of why the LIGO-Virgo collaboration came to the opposite conclusion. Scalar polarization, however, is ruled out by the data. Confirmation of a vector polarization component of gravitational waves would be a sign of post-general-relativity physics. (paper)