Axion gravitodynamics, Lense-Thirring effect, and gravitational waves

TL;DR

This paper explores a gravitational analog of axion electrodynamics involving a parity-violating theta term, predicting effects much stronger than previous models, with potential detectability through satellite and gravitational wave observations.

Contribution

It introduces axion gravitodynamics based on the Nieh-Yan invariant, revealing significantly amplified observable effects compared to gravitational Chern-Simons theories.

Findings

Over 80 orders of magnitude stronger effects than Chern-Simons gravity.

Derived corrections to the Lense-Thirring effect consistent with satellite data.

Modified gravitational wave dispersion relations with bounds from GW170817.

Abstract

We investigate physical implications of a gravitational analog of axion electrodynamics with a parity-violating gravitoelectromagnetic theta term. This is related to the Nieh-Yan topological invariant in gravity with torsion, in contrast to the well-studied gravitational Chern-Simons term quadratic in curvature, coupled via a dynamical axionlike scalar field. Axion gravitodynamics is the corresponding linearized theory. We find that potentially observable effects are over 80 orders of magnitude stronger than for its Chern-Simons counterpart and could be in reach for detection by experiments in the near future. For a near-Earth scenario, we derive corrections to the Lense-Thirring effect and compare them to data from satellite-based experiments (Gravity Probe B). For gravitational waves, we find modified dispersion relations, derive the corresponding polarization-dependent modified group and phase velocities, and compare them to data from neutron star mergers (GW170817) to derive even stronger bounds.