EVOLUTION OF THE UNIVERSE AND DARK ENERGY MYSTERY

Abstract

We study the evolving universe in the presence of dark energy via different well-known cosmological parameters. Firstly, we consider interacting new holographic dark energy model with cold dark matter in non-flat FRW uni- verse. We obtain the equation of state parameter which represents the evo- lution of the universe from vacuum dark energy region towards quintessence region for particular values of the constant parameters. It is found that this model always remains unstable against small perturbations. The correspon- dence of this model with quintessence, tachyon, k-essence and dilaton scalar field models is also established. The dynamics of scalar fields and potentials provide consistent behavior with the accelerated expansion of the universe. We also consider interacting generalized holographic dark energy with cold dark matter in non-flat universe. We find that the deceleration parameter lies in the accelerated expansion phase of the universe and the equation of state parameter provides quintom like nature. This dark energy model is stable against small perturbations for specific range of constant parame- ters. It is found that the quintessence and tachyon potentials correspond to scaling solutions. Secondly, the pilgrim dark energy phenomenon is explored by choosing three cutoffs such as Hubble as well as event horizon and conformal age of the universe in flat universe. We study the pilgrim dark energy which plays an effective role on the equation of state parameter for exploring phantom region of the universe. The freezing region is found in the ω Λ − ω Λ plane and the ΛCDM is achieved in the statefinders plane for all three models of pilgrim dark energy. The conjecture of pilgrim dark energy is also studied by xixii assuming the apparent and event horizons in non-flat universe and develop ω Λ − ω Λ as well as r − s plane. It is interesting to mention here that the pilgrim dark energy with event horizon yields phantom region for all cases of d 2 with u < 0. For these models, ω Λ − ω Λ plane provides the thawing as well as freezing region and ΛCDM limit. The r − s plane shows the correspondence with different models such as quintessence and phantom dark energy, ΛCDM and chaplygin gas. Also, we investigate the validity of the generalized second law of thermodynamics with event horizon in flat as well as non-flat universe. Finally, we consider the modified holographic dark energy interacting with cold dark matter with varying G in flat and non-flat Kaluza-Klein universes. For this dark energy model, we assume event horizon as an infrared cutoff scale. We discuss the equation of state parameter and check the validity of the generalized second law of thermodynamics. In non-flat Kaluza-Klein case, we investigate the s−r plane in which the corresponding curves meet the limit of ΛCDM model .