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Time evolution of dark energy and other cosmological parameters

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This article is a continuation of a former article, taking account of recent observational results among others from the Planck mission. The adopted approach starts considering a hot big bang scenario for a universe with Friedmann-LemaĆ®tre-Robertson-Walker metric, the spatial curvature parameter k = 0 and the cosmological constant Λ = 0 . It does not contradict the standard model (now called “Λ-CDM model”) except on a point: the acceleration of the expansion of the universe is not related to the cosmological constant but to a “dark energy” component α which is mostly constant in time and is a constitutive part of the Hubble parameter. Using a reversed method, it is shown that the scale factor evolves in a similar way as in the Λ-CDM model for the past epochs but that the acceleration in the future is less pronounced. The evolution of several cosmological parameters from the end of an inflationary stage till now is given as was done in the former article. The major difference is that, instead of imposing the pressure to be nil at present time in order to comply with the equation of state for the matter-dominated era, the pressure‐density ratio is left free to be negative. The pressure then naturally becomes negative around 7.12 Gyrs after the big bang. It is shown that the contribution of dark energy is negligible during the radiation-dominated era but becomes of the order of the contribution of matter during the matter-dominated era which solves the coincidence problem. The existence of a possible interaction term between dark energy and matter (or radiation) contributing to the density is put into evidence.
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Keywords: Acceleration of the Expansion; Big Bang; Dark Energy; Dark Matter; Density; Evolution of the Scale Factor; Inflation; Negative Pressure

Document Type: Research Article

Publication date: September 15, 2017

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  • Physics Essays has been established as an international journal dedicated to theoretical and experimental aspects of fundamental problems in Physics and, generally, to the advancement of basic knowledge of Physics. The Journal's mandate is to publish rigorous and methodological examinations of past, current, and advanced concepts, methods and results in physics research. Physics Essays dedicates itself to the publication of stimulating exploratory, and original papers in a variety of physics disciplines, such as spectroscopy, quantum mechanics, particle physics, electromagnetic theory, astrophysics, space physics, mathematical methods in physics, plasma physics, philosophical aspects of physics, chemical physics, and relativity.
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