  In this paper, we investigate the sensitivity to additional gravitational
wave polarization modes of future detectors. We first look at the upcoming
Einstein Telescope and its combination with existing or planned Earth-based
detectors in the case of a stochastic gravitational wave background. We then
study its correlation with a possible future space-borne detector sensitive to
high-frequencies, like DECIGO. Finally, we adapt those results for a single GW
source and establish the sensitivity of the modes, as well as the localization
on the sky.
