Odd parity gravitational waves in modified Bianchi I cosmology

Abstract

In this study, we primarily examine the behavior of axial (odd parity) gravitational waves (GWs) in an initially Bianchi Type-I Universe, with a particular focus on the influence of a scalar field within the framework of theory. To this end, we employ the Regge–Wheeler perturbation framework, with a particular emphasis on the axial mode. Using these axial perturbations, we derive the perturbed field equations after formulating the field equations for the unperturbed cosmological model. Our results indicate that the scalar field primarily influences the temporal components of the perturbations, whereas the spatial components exhibit sinusoidal wave-like behavior. These findings provide new insights into the interplay between scalar fields and GWs, with potential implications for understanding the dynamics of the early Universe and testing modified gravity theories.