Precision cosmology from future lensed gravitational wave and
  electromagnetic signals
  The standard siren approach of gravitational wave cosmology appeals to the
direct luminosity distance estimation through the waveform signals from
inspiralling double compact binaries, especially those with electromagnetic
counterparts providing redshifts. It is limited by the calibration
uncertainties in strain amplitude and relies on the fine details of the
waveform. The Einstein Telescope is expected to produce $10^4-10^5$
gravitational wave detections per year, $50-100$ of which will be lensed. Here
we report a waveform-independent strategy to achieve precise cosmography by
combining the accurately measured time delays from strongly lensed
gravitational wave signals with the images and redshifts observed in the
electromagnetic domain. We demonstrate that just 10 such systems can provide a
Hubble constant uncertainty of $0.68\%$ for a flat Lambda Cold Dark Matter
universe in the era of third generation ground-based detectors.
