Cosmic opacity: cosmological-model-independent tests from gravitational
  waves and Type Ia Supernova
  In this paper, we present a scheme to investigate the opacity of the Universe
in a cosmological-model-independent way, with the combination of current and
future available data in gravitational wave (GW) and electromagnetic (EM)
domain. In the FLRW metric, GWs propagate freely through a perfect fluid
without any absorption and dissipation, which provides a distance measurement
unaffected by the cosmic opacity. Focusing on the simulated data of
gravitational waves from the third-generation gravitational wave detector (the
Einstein Telescope, ET), as well as the newly-compiled SNe Ia data (JLA and
Pantheon sample), we find an almost transparent universe is strongly favored at
much higher redshifts ($z\sim 2.26$). Our results suggest that, although the
tests of cosmic opacity are not significantly sensitive to its parametrization,
a strong degeneracy between the cosmic opacity parameter and the absolute
\textit{B}-band magnitude of SNe Ia is revealed in this analysis. More
importantly, we obtain that future measurements of the luminosity distances of
gravitational waves sources will be much more competitive than the current
analyses, which makes it expectable more vigorous and convincing constraints on
the cosmic opacity (and consequently on background physical mechanisms) and a
deeper understanding of the intrinsic properties of type Ia supernovae in a
cosmological-model-independent way.
