Impact of alternative theories of gravity on current cosmic scenarios

Abstract

This thesis incorporates the study of some current cosmic scenarios in the realm of alternative theories of gravity (curvature and torsion based theories). These scenarios include gravitational baryogenesis phenomenon, cosmic accelerating expansion of the universe and thermodynamic analysis. Firstly, we examine the matter-antimatter asymmetry through the gravitational baryogenesis and its generalized mechanisms for some well-known curvature and torsion-based models. The absence of intense radiation from matter/anti-matter annihilation, cosmic microwave background and big bang nucleosynthesis strongly suggested that there exists more matter than anti-matter in our universe. Observational constraints verified that the baryon number density 𝜂𝐵 to entropy 𝑆 ratio is approximately 𝜂𝐵 𝑆 ∼ 9.42 × 10−11. We compute the baryon to entropy ratio for all models and get some consistent results. Secondly, we investigate the evolution of some cosmic parameters and planes in the framework of DGP braneworld model. We assume interaction between Barrow holographic dark energy model (whose infrared cutoffs scale are set by Hubble and event horizons) and pressureless dark matter. We check the behavior of different cosmological parameters like Hubble, equation of state, deceleration, squared speed of sound, statefinder plane and 𝜔𝜗 − 𝜔𝜗 ′ plane. Also, the thermodynamic nature of the underlying model through Barrow entropy as horizon entropy is investigated. Finally, we consider Tsallis holographic dark energy model with event and apparent horizons as infrared cutoff in the framework of dynamical Chern-Simons modified gravity. The impact of non-flat FRW universe is being taken into account to explore some cosmological parameters like Hubble, equation of state, deceleration and squared speed of sound. Finally, we investigate the generalized second law of thermodynamics with Tsallis entropy for both horizons and find some interesting outcomes.