Gravitational Wave Opacity from Gauge Field Dark Energy
  We show that astrophysical gravitational waves can undergo an anomalous
modulation when propagating through cosmic gauge field dark energy. A
sufficiently strong effect, dependent on the gauge field energy density, would
appear as a redshift-dependent opacity, thereby impacting the use of
gravitational wave standard sirens to constrain the expansion history of the
Universe. We investigate a particular model of cosmic gauge field dark energy
and show that at early times it behaves like dark radiation, whereas a novel
interaction causes it to drive cosmic acceleration at late times. Joint
constraints on the cosmological scenario due to type 1a supernovae, baryon
acoustic oscillations, and cosmic microwave background data are presented. In
view of these constraints, we show that standard siren luminosity distances in
the redshift range 0.5 < z < 1.5 would systematically dim by up to 1%, which
may be distinguishable by third-generation gravitational wave detectors.
