scholarly journals Dark Energy and the Time Dependence of Fundamental Particle Constants

2020 ◽  
pp. 2000072
Author(s):  
Bodo Lampe
Keyword(s):  
Dark Energy ◽  
Time Dependence ◽  
Fundamental Particle

scholarly journals Temperature variation in the dark cosmic fluid in the late universe

2016 ◽  
Vol 31 (08) ◽  
pp. 1650050 ◽  
Author(s):  
Iver Brevik
Keyword(s):  
Dark Energy ◽  
Time Dependence ◽  
Entropy Production ◽  
Temperature Variation ◽  
Temperature Jump ◽  
Fluid Model ◽  
Maxwell Fluid ◽  
Positive Temperature ◽  
Turbulent Transition ◽  
Big Rip

A one-component dark energy fluid model of the late universe is considered [Formula: see text] when the fluid, initially assumed laminar, makes a transition into a turbulent state of motion. Spatial isotropy is assumed so that only the bulk viscosities are included ([Formula: see text] in the laminar epoch and [Formula: see text] in the turbulent epoch). Both viscosities are assumed to be constants. We derive a formula, new as far as we know, for the time dependence of the temperature [Formula: see text] in the laminar case when viscosity is included. Assuming that the laminar/turbulent transition takes place at some time [Formula: see text] before the big rip is reached, we then analyze the positive temperature jump experienced by the fluid at [Formula: see text] if [Formula: see text]. This is just as one would expect physically. The corresponding entropy production is also considered. A special point emphasized in the paper is the analogy that exists between the cosmic fluid and a so-called Maxwell fluid in viscoelasticity.

scholarly journals Probing the time dependence of dark energy

2012 ◽  
Vol 2012 (02) ◽  
pp. 042-042 ◽  
Author(s):  
Edésio M Barboza ◽  
J.S Alcaniz
Keyword(s):  
Dark Energy ◽  
Time Dependence

scholarly journals DARK ENERGY: RECENT DEVELOPMENTS

2006 ◽  
Vol 21 (14) ◽  
pp. 1083-1097 ◽  
Author(s):  
N. STRAUMANN
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Particle Physics ◽  
Vacuum Energy ◽  
Large Body ◽  
Vacuum Energy Density ◽  
Fundamental Particle ◽  
Dark Energy Component ◽  
Recent Developments

A six-parameter cosmological model, involving a vacuum energy density that is extremely tiny compared to fundamental particle physics scales, describes a large body of increasingly accurate astronomical data. In the first part of this brief review we summarize the current situation, emphasizing recent progress. An almost infinitesimal vacuum energy is only the simplest candidate for a cosmologically significant nearly homogeneous exotic energy density with negative pressure, generically called Dark Energy. If general relativity is assumed to be also valid on cosmological scales, the existence of such a dark energy component that dominates the recent universe is now almost inevitable. We shall discuss in the second part the alternative possibility that general relativity has to be modified on distances comparable to the Hubble scale. It will turn out that observational data are further restricting theoretical speculations. Moreover, some of the recent proposals have serious defects on a fundamental level (ghosts, acausalities, superluminal fluctuations).

scholarly journals Observational constraints on the time-dependence of dark energy

2006 ◽  
Vol 732 (1-2) ◽  
pp. 379-387 ◽  
Author(s):  
Deepak Jain ◽  
J.S. Alcaniz ◽  
Abha Dev
Keyword(s):  
Dark Energy ◽  
Time Dependence ◽  
Observational Constraints

scholarly journals Time Dependence of Cosmological Parameters in the Framework of Brans-Dicke Theory

2019 ◽  
pp. 242-254
Author(s):  
Sudipto Roy ◽  
Avik Ghosh ◽  
Adrika Dasgupta
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Time Dependence ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Scale Factor ◽  
Accelerated Expansion ◽  
Eos Parameter ◽  
Expansion Time ◽  
Time Variations

In the framework of Brans-Dicke (BD) theory of gravitation, the time dependence of some cosmological parameters have been determined in the present study, for an universe having a FRW space-time with zero spatial curvature. The time variations of the energy density, BD parameter, equation of state (EoS) parameter have been determined, from the field equations of the BD theory, in the initial part of this model. For this purpose, we have used ansatzes relating the scalar field with the scale factor and also linking the BD parameter with the scalar field. For these calculations, an empirical expression for the scale factor has been used. This scale factor has been so chosen that it leads to a signature flip of the deceleration parameter from positive to negative in the course of its evolution with time, indicating a change of phase from decelerated expansion to accelerated expansion. Time dependence of the density parameters for matter and dark energy has also been studied here. Using their expressions we have determined the time dependence of the densities of matter and dark energy. The time variations of all these parameters have been shown graphically. Apart from them, we have also shown the variations of the deceleration parameter and the BD parameter as functions of the scalar field graphically.

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