Probing general relativistic spin-orbit coupling with gravitational waves from hierarchical triple systems

TL;DR

This paper investigates the gravitational spin Hall effect on gravitational waves from hierarchical triple black hole systems, exploring how spacetime curvature influences wave propagation and its potential for experimental detection.

Contribution

It introduces the first analysis of the gravitational spin Hall effect in strong-field triple black hole systems and assesses its impact on gravitational waveforms.

Findings

Gravitational spin Hall effect causes polarization-dependent waveform modifications.

The effect is significant enough to be potentially observable with current or future detectors.

Detection would provide new tests of general relativity in strong-field regimes.

Abstract

Wave packets propagating in inhomogeneous media experience a coupling between internal and external degrees of freedom and, as a consequence, follow spin-dependent trajectories. These phenomena, well known in optics and condensed matter physics, are referred to as spin Hall effects. Similarly, the gravitational spin Hall effect is expected to affect the propagation of gravitational waves on curved spacetimes. In this general-relativistic setup, the curvature of spacetime acts as impurities in a semiconductor or inhomogeneities in an optical medium, leading to a frequency- and polarization-dependent propagation of wave packets. In this letter, we study this effect for strong-field lensed gravitational waves generated in hierarchical triple black hole systems in which a stellar-mass binary merges near a more massive black hole. We calculate how the gravitational spin Hall effect modifies the gravitational waveforms and show its potential for experimental observation. If detected, these effects will have profound implications for astrophysics and tests of general relativity.