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

Understand

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.