Parity violation in framework of nonmetricity gravity

The latest observational data of the Planck satellite show a nontrivial value of polarization rotation angle caused by cosmic birefringence in the early universe. Moreover, the asymmetry of baryons versus anti-baryons still remains mysterious. Both of them indicate that there should be hidden new physics, such as fundamental symmetry breaking. In this paper, we try to interpret these two events in the framework of nonmetricity modified gravity. We introduce an interaction term between the nonmetricity-based function and matter current, and calculate both the rotation angle and baryon-to-photon ratio. We also constrain the model parameters using the current observational data. With some specific examples, we demonstrate that in nonmetric gravity theory, these two events can be interpreted in a unified way. Nevertheless, in this case, the minimal coupling of the nonmetricity scalar and the matter current might not be favored.