Unifying an asymmetric bounce to the dark energy in Chern–Simons F(R) gravity

Abstract

We propose a cosmological scenario in which the universe undergoes through a non-singular bounce, and after the bounce, it decelerates having a matter-like dominated evolution during some regime of the deceleration era, and finally at the present epoch it evolves through an accelerating stage. Our aim is to study such evolution in the context of Chern–Simons corrected F(R) gravity theory and confront the model with various observational data. Using the reconstruction technique, and in addition by employing suitable boundary conditions, we determine the form of F(R) for the entire possible range of the cosmic time. The form of F(R) seems to unify a non-singular bounce with a dark energy epoch, in particular, from a non-singular bounce to a deceleration epoch and from a deceleration epoch to a late time acceleration era. It is important to mention that the bouncing scenario in the present context is an asymmetric bounce, in particular, the Hubble radius monotonically increases and asymptotically diverges at the late contracting era, while it seems to decrease with time at the present epoch. The decreasing behaviour of the Hubble radius ensures a late time acceleration era of the universe. Moreover, due to the aforesaid evolution of the Hubble radius, the primordial perturbation modes generate at the deep contracting era far away from the bounce when all the perturbation modes lie within the horizon. Correspondingly we calculate the scalar and tensor power spectra, and accordingly, we evaluate the primordial observable quantities like the spectral index of the scalar curvature perturbation, the tensor-to-scalar ratio, and as a result, they are found to be in agreement with the latest Planck 2018 constraints. In this regard, the Chern–Simons term seems to have considerable effects on the tensor perturbation evolution, however keeping intact the scalar part of the perturbation with that of in the case of a vacuum F(R) model, and as a result, the Chern–Simons term proves to play an important role in making the observable quantities consistent with the Planck results. Furthermore the theoretical expectation of the effective equation of state parameter of the dark energy epoch is confronted with the Planck+SNe+BAO data.