Gravitational Waves in ECSK theory: Robustness of mergers as standard
  sirens and nonvanishing torsion
  The amplitude propagation of gravitational waves in an
Einstein-Cartan-Sciamma-Kibble (ECSK) theory is studied by assuming a dark
matter spin tensor sourcing for spacetime torsion at cosmological scales. The
analysis focuses on a weak-torsion regime, such that gravitational wave
emission, at leading and subleading orders, does not deviate from standard
General Relativity. We show that, in principle, the background torsion induced
by an eventual dark matter spin component could lead to an anomalous dampening
or amplification of the gravitational wave amplitude, after going across a long
cosmological distance. The importance of this torsion-induced anomalous
propagation of amplitude for binary black hole mergers is assessed. For
realistic late-universe astrophysical scenarios, the effect is tiny and falls
below detection thresholds, even for near-future interferometers such as LISA.
To detect this effect may not be impossible, but it is still beyond our
technological capabilities.
