Post-Newtonian parameters of ghost-free parity-violating gravities

TL;DR

This paper analyzes a ghost-free parity-violating gravity theory within the PPN framework, finding it largely consistent with general relativity except for an extra parameter, and uses Gravity Probe B data to constrain the model.

Contribution

It derives the complete PPN parameters for the ghost-free PV gravity theory and identifies an additional parameter affecting gravitomagnetic effects.

Findings

All PPN parameters match GR except for one extra parameter κ.

The extra parameter κ influences gravitomagnetic precession.

Gravity Probe B data constrains the model parameters.

Abstract

We investigate the slow-motion and weak-field approximation of the general ghost-free parity-violating (PV) theory of gravity in the parametrized post-Newtonian (PPN) framework and derive the perturbative field equations, which are modified by the PV terms of this theory. The complete PPN parameters are obtained by solving the perturbative field equations. We find that all the PPN parameters are exactly the same as those in general relativity, except for an extra parameter $\kappa$, which is caused by the new curl-type term in the gravitomagnetic sector of the metric in this theory. We calculate the precession effects of gyroscopes in this theory and constrain the model parameters by the observations of the Gravity Probe B experiment.