An oscillating Chern-Simons universe crossing the phantom divide line and alleviating the Hubble tension

Abstract

In order to alleviate the Hubble tension, we propose a new law for the Hubble parameter that varies periodically with time and we study the validity of the dynamics of a flat Friedmann–Robertson–Walker Universe in the context of a generalized Chern–Simons modified gravity (CSMG). We prove that for specific numerical values of the free parameters in the theory, the phantom divide line is crossed and the universe undergoes decelerating expansion and accelerating expansion alternately without singularity. The deceleration and the jerk parameters oscillate also around numerical values in agreement with astronomical BAO+Pantheon SNeIa+Cosmic Chronometers observations.