Studies on dark matter dark energy and possible alternate models

Abstract

The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the universe is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM are clearly ruled out, there is still a plethora of viable particles that fit the bill. In the context of DE, while current observations favour a cosmological constant picture, there are other competing models which may be equally likely. The standard model for the formation of structure assumes that there newlineexisted small fluctuations in the early universe that grew due to gravitational instability. The origin of these fluctuations are still unclear. In this study, we proposed the role of dark matter in providing the seed for star formation in the early universe, which is supported by very recent observations. With this we set observable constraints on luminosities, temperatures, and lifetimes of the early stars with an admixture of dark matter. We also studied the effects of the background repulsive dark energy density for large scale cosmic structures. The relation, and#119872;and#8260;and#119877;2 and#8776; 1and#119892;/and#119888;and#119898;2, seems to hold true for primeval galaxies as well as those at present epoch. From this, we set constraints on the nature and evolution of dark energy. Besides, we also set constraints on the size of galaxy clusters and superclusters due to the repulsive cosmological dark energy. This could indicate as to why large scale cosmic structures much larger than and#8764;200 Mpc are not seen.This study also looked at the evolution of the concept of the cosmological constant from its inception a little over a hundred years ago when Einstein introduced the cosmological constant in his General Theory of Relativity newlinein order to obtain a static universe to conform to the philosophical view of newlinethe universe at that time to it possibly making up close to about 70% of the energy density of the universe.