Parity violating scalar-tensor model in teleparallel gravity and its cosmological application

Abstract

The parity violating model based on teleparallel gravity is a competitive scheme for parity violating gravity, which has been preliminary studied in the literature. To further investigate the parity violating model in teleparallel gravity, in this paper, we construct all independent parity-odd terms that are quadratic in torsion tensor and coupled to a scalar field in a way without higher-order derivatives. Using these parity-odd terms, we formulate a general parity violating scalar-tensor model in teleparallel gravity and obtain its equations of motion. To explore potentially viable models within the general model, we investigate the cosmological application of a submodel of the general model in which terms above the second power of torsion are eliminated. We focus on analyzing cosmological perturbations and identify the conditions that preserve the parity violating signal of gravitational waves at linear order while avoiding the ghost instability.

Constraints on the ghost-free parity-violating gravity from laser-ranged satellites

“…In the strong field regime, the most direct tests of gravity are the signals of gravitational wave events, especially parityviolating gravity, whose presence affects the propagation and production of gravitational waves. The presence of the parity violation in gravity induces amplitude or/and velocity birefringence in the propagation of GWs [14,20,[41][42][43][44][45][46]. These parity-violating effects have been examined using gravitational wave event data for various precision tests, like searching for birefringence effects or constraints on the parameters of the theory [20,25,[47][48][49][50][51][52].…”