scholarly journals Determining Evolution of Cosmological Constant, Gravitational Constant and Speed of Light Using Nonadiabatic Cosmological Model and LLR Findings

Galaxies ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 67
Author(s):  
Gupta
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Gravitational Constant ◽  
Friedmann Equation ◽  
Distance Modulus ◽  
Significant Finding ◽  
Speed Of Light ◽  
Lunar Laser Ranging ◽  
Data Set ◽  
Λcdm Model

We have shown that the Hubble constant H0 embodies the information about the evolutionary nature of the cosmological constant Λ, gravitational constant G, and the speed of light c. We have derived expressions for the time evolution of G/c2 (≡K) and dark energy density εΛ related to Λ by explicitly incorporating the nonadiabatic nature of the universe in the Friedmann equation. We have found (dK/dt)/K = 1.8H0 and, for redshift z, εΛ,z/εΛ,0 = 0.4+0.61+z-1.52. Since the two expressions are related, we believe that the time variation of K (and therefore that of G and c) is manifested as dark energy in cosmological models. When we include the null finding of the lunar laser ranging (LLR) for (dG/dt)/G and relax the constraint that c is constant in LLR measurements, we get (dG/dt)/G = 5.4H0 and (dc/dt)/c = 1.8H0. Further, when we adapt the standard ΛCDM model for the z dependency of εΛ rather than it being a constant, we obtain surprisingly good results fitting the SNe Ia redshift z vs distance modulus µ data. An even more significant finding is that the new ΛCDM model, when parameterized with low redshift data set (z < 0.5), yields a significantly better fit to the data sets at high redshifts (z > 0.5) than the standard ΛCDM model. Thus, the new model may be considered robust and reliable enough for predicting distances of radiation emitting extragalactic redshift sources for which luminosity distance measurement may be difficult, unreliable, or no longer possible.

scholarly journals Testing the effect of H0 on fσ8 tension using a Gaussian Process method

2020 ◽  
Author(s):  
En-Kun Li ◽  
Minghui Du ◽  
Zhi-Huan Zhou ◽  
Hongchao Zhang ◽  
Lixin Xu
Keyword(s):  
Growth Rate ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Gaussian Process ◽  
Dark Energy Model ◽  
Hubble Space Telescope ◽  
Λcdm Model ◽  
Space Distortion ◽  
Best Fit ◽  
Process Method

Abstract Using the fσ8(z) redshift space distortion (RSD) data, the $\sigma _8^0-\Omega _m^0$ tension is studied utilizing a parameterization of growth rate f(z) = Ωm(z)γ. Here, f(z) is derived from the expansion history H(z) which is reconstructed from the observational Hubble data applying the Gaussian Process method. It is found that different priors of H0 have great influences on the evolution curve of H(z) and the constraint of $\sigma _8^0-\Omega _m^0$. When using a larger H0 prior, the low redshifts H(z) deviate significantly from that of the ΛCDM model, which indicates that a dark energy model different from the cosmological constant can help to relax the H0 tension problem. The tension between our best-fit values of $\sigma _8^0-\Omega _m^0$ and that of the Planck 2018 ΛCDM (PLA) will disappear (less than 1σ) when taking a prior for H0 obtained from PLA. Moreover, the tension exceeds 2σ level when applying the prior H0 = 73.52 ± 1.62 km/s/Mpc resulted from the Hubble Space Telescope photometry. By comparing the $S_8 -\Omega _m^0$ planes of our method with the results from KV450+DES-Y1, we find that using our method and applying the RSD data may be helpful to break the parameter degeneracies.

MAXWELL BRANE COSMOLOGY WITH HIGHER-ORDER STRING CURVATURE CORRECTIONS, A NONMINIMALLY COUPLED SCALAR FIELD, DARK MATTER–DARK ENERGY INTERACTION AND A VARYING SPEED OF LIGHT

2009 ◽  
Vol 18 (02) ◽  
pp. 289-318 ◽  
Author(s):  
R. A. EL-NABULSI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Friedmann Equation ◽  
Building Blocks ◽  
Higher Order ◽  
Alternative Theory ◽  
Speed Of Light ◽  
Energy Interaction ◽  
Curvature Term

We investigate the cosmological effects of an alternative theory of gravity on the four-dimensional Randall–Sundrum braneworld of type II with a higher-order string curvature term added to the action. We discuss the possibility of a varying speed of light, which has recently attracted considerable attention, in the presence a Maxwell field and of a dynamically evolving bulk scalar field nonminimally coupled to scalar curvature in a quadratic form, together with a dark matter–dark energy interaction term. After deriving the modified Friedmann equation on the brane, as well as the scalar field equations, we then analyze the dynamical equations obtained so far. Special attention is paid to scaling solutions which could be important building blocks in constructing the models of dark energy. The constructed model exhibits several features of cosmological and astrophysical interest for both the early and the late universe, consistent with recent observations, in particular the ones concerned with celerity of light, four and five gravitational constants, black hole masses and entropies.

scholarly journals Statefinder and Om Diagnostics for New Generalized Chaplygin Gas Model

Universe ◽  
2021 ◽  
Vol 7 (10) ◽  
pp. 362
Author(s):  
Abdulla Al Mamon ◽  
Vipin Chandra Dubey ◽  
Kazuharu Bamba
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Observational Data ◽  
Hubble Parameter ◽  
Chaplygin Gas ◽  
Distance Modulus ◽  
Generalized Chaplygin Gas ◽  
New Model ◽  
Λcdm Model ◽  
Data Points

We explore a unified model of dark matter and dark energy. This new model is a generalization of the generalized Chaplygin gas model and is known as a new generalized Chaplygin gas (NGCG) model. We study the evolutions of the Hubble parameter and the distance modulus for the model under consideration and the standard ΛCDM model and compare that with the observational datasets. Furthermore, we demonstrate two geometric diagnostics analyses including the statefinder (r,s) and Om(z) to the discriminant NGCG model from the standard ΛCDM model. The trajectories of evolution for (r,s) and Om(z) diagnostic planes are shown to understand the geometrical behavior of the NGCG model by using different observational data points.

scholarly journals DARK ENERGY AS A RELIC OF THE VACUUM-ENERGY CANCELLATION?

2008 ◽  
Vol 17 (01) ◽  
pp. 111-133
Author(s):  
ORCHIDEA MARIA LECIAN ◽  
GIOVANNI MONTANI
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Gravitational Interaction ◽  
Friedmann Equation ◽  
Vacuum Energy Density ◽  
De Sitter ◽  
Frw Universe ◽  
First Case ◽  
Present Universe

We analyze the dynamical implications of an exponential Lagrangian density for the gravitational field, as referred to an isotropic FRW Universe. Then, we discuss the features of the generalized de Sitter phase, predicted by the new Friedmann equation. The existence of a consistent de Sitter solution arises only if the ratio between the vacuum energy density and that associated with the fundamental length of the theory acquires a tantalizing negative character. This choice allows us to explain the present Universe dark energy as a relic of the vacuum-energy cancellation due to the cosmological constant intrinsically contained in our scheme. The corresponding scalar-tensor description of the model is addressed too, and the behavior of the scalar field is analyzed for both negative and positive values of the cosmological term. In the first case, the Friedmann equation is studied both in vacuum and in the presence of external matter, while, in the second case, the quantum regime is approached in the framework of "repulsive" properties of the gravitational interaction, as described in recent issues in loop quantum cosmology. In particular, in the vacuum case, we find a pure non-Einsteinian effect, according to which a negative cosmological constant provides an accelerating de Sitter dynamics, in the region where the series expansion of the exponential term does not hold.

scholarly journals Constraining a Possible Variation of G with Type Ia Supernovae

2014 ◽  
Vol 31 ◽  
Author(s):  
Jeremy Mould ◽  
Syed A. Uddin
Keyword(s):  
Dark Energy ◽  
Task Force ◽  
Rate Of Change ◽  
Laser Ranging ◽  
Lunar Laser Ranging ◽  
Data Set ◽  
Lunar Laser ◽  
Standard Candle ◽  
Type Ia ◽  
Ia Supernovae

AbstractAstrophysical cosmology constrains the variation of Newton’s Constant in a manner complementary to laboratory experiments, such as the celebrated lunar laser ranging campaign. Supernova cosmology is an example of the former and has attained campaign status, following planning by a Dark Energy Task Force in 2005. In this paper, we employ the full SNIa data set to the end of 2013 to set a limit on G variation. In our approach, we adopt the standard candle delineation of the redshift distance relation. We set an upper limit on its rate of change $|\dot{G}/G|$ of 0.1 parts per billion per year over 9 Gyrs. By contrast, lunar laser ranging tests variation of G over the last few decades. Conversely, one may adopt the laboratory result as a prior and constrain the effect of variable G in dark energy equation of state experiments to δw < 0.02. We also examine the parameterisation G ~ 1 + z. Its short expansion age conflicts with the measured values of the expansion rate and the density in a flat Universe. In conclusion, supernova cosmology complements other experiments in limiting G variation. An important caveat is that it rests on the assumption that the same mass of 56Ni is burned to create the standard candle regardless of redshift. These two quantities, f and G, where f is the Chandrasekhar mass fraction burned, are degenerate. Constraining f variation alone requires more understanding of the SNIa mechanism.

scholarly journals Teleparallel Poincaré cosmology and ΛCDM model

2014 ◽  
Vol 23 (06) ◽  
pp. 1450057
Author(s):  
Wenjie Lu ◽  
Wolung Lee ◽  
Kin-Wang Ng
Keyword(s):  
Dark Energy ◽  
Gauge Theory ◽  
General Theory ◽  
Cosmological Constant ◽  
Cosmic Acceleration ◽  
Accelerating Universe ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Λcdm Model

We apply the teleparallelism condition to the Poincaré gauge theory (PGT) of gravity. The resultant teleparallelized cosmology is completely equivalent to the Friedmann cosmology derived from Einstein's general theory of relativity. The torsion is shown to play the role of the cosmological constant driving the cosmic acceleration. We then extend such theory to include the effect of spin and explore the possibility of accounting for the current accelerating universe by a spinning dark energy.

scholarly journals PHYSICAL CONSTANTS AND THE GURZADYAN–XUE FORMULA FOR THE DARK ENERGY

2006 ◽  
Vol 21 (09) ◽  
pp. 729-733 ◽  
Author(s):  
G. V. VERESHCHAGIN
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Vacuum Energy ◽  
Gravitational Constant ◽  
Vacuum Energy Density ◽  
Speed Of Light ◽  
Dark Energy Density ◽  
Physical Constants ◽  
A Value ◽  
Cosmological Context

We consider cosmological implications of the formula for the dark energy density derived by Gurzadyan and Xue1,2 which predicts a value fitting the observational one. Cosmological models with varying by time physical constants, namely, speed of light and gravitational constant and/or their combinations, are considered. In one of the models, for example, vacuum energy density induces effective negative curvature, while another one has an unusual asymptotic. This analysis also explicitly rises the issue of the meaning and content of physical units and constants in cosmological context.

scholarly journals A MODIFIED FRW METRIC TO EXPLAIN THE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 27 (19) ◽  
pp. 1250106 ◽  
Author(s):  
S. ZORBA
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Energy Content ◽  
Friedmann Equation ◽  
Angular Frequency ◽  
Rotational Energy ◽  
Simple Argument ◽  
Average Value ◽  
Frw Metric ◽  
Constant Dark

One of the most outstanding problems of the standard model of cosmology today is the problem of cosmological constant/dark energy. It corresponds to about 73% of the energy content of the universe gone missing. I hereby postulate a modified FRW metric for our universe, which animates a universe spinning very slowly with an angular frequency that is equal to the Hubble's constant. It is shown by a simple argument that in such a universe there will be an overlooked rotational energy whose average value is identically equal to the matter-energy content of this universe as observed by a coordinate observer. The corresponding Friedmann equation is derived, whereby the overlooked rotational energy naturally becomes the cosmological constant/dark energy term without artificially/mysteriously adding any such term, as is commonly done. The proposed model also produces Hubble's law naturally.

scholarly journals Astrometric Solar-System Anomalies and Evolutionary Physical Constants

2019 ◽  
Author(s):  
Rajendra P. Gupta
Keyword(s):  
Solar System ◽  
Gravitational Constant ◽  
Hubble Constant ◽  
Secular Change ◽  
Distance Modulus ◽  
Astronomical Unit ◽  
Speed Of Light ◽  
New Approach ◽  
Orbit Eccentricity ◽  
Secular Increase

We have shown that three astrometric solar-system anomalies can be explained satisfactorily by using evolutionary gravitational constant G and speed of light c in the Einstein&rsquo;s field equation. These are: a) the Pioneer acceleration anomaly; b) the anomalous secular increase of Moon-orbit eccentricity; and c) the anomalous secular change in the astronomical unit AU. The gravitational constant G and the speed of light c both increase as dG/dt = 5.4GH0 and dc/dt = 1.8cH0 with H0 as the Hubble constant. We also show that the Planck&rsquo;s constant ħ increases as dħ/dt = 1.8ħH0.&nbsp; Additionally, the new approach fits the supernovae Ia redshift vs distance modulus data as well as the standard &Lambda;CDM model with just one adjustable parameter H0.

scholarly journals SNe data analysis in variable speed of light cosmologies without cosmological constant

2014 ◽  
Vol 29 (24) ◽  
pp. 1450103 ◽  
Author(s):  
Pengfei Zhang ◽  
Xinhe Meng
Keyword(s):  
Dark Energy ◽  
Scale Factor ◽  
Model Parameters ◽  
Type Ia Supernovae ◽  
Distance Modulus ◽  
Data Sets ◽  
Variable Speed ◽  
Speed Of Light ◽  
Type Ia ◽  
Ia Supernovae

In this work, we aim to show the possibilities of the variable speed of light (VSL) theory in explaining the type Ia supernovae (SNe) observations without introducing dark energy. The speed of light is assumed to be scale factor-dependent, which is the most popular assumption in VSL theory. We show the modified calculation of the distance modulus and the validity of the redshift-scale factor relation in VSL theory. Three different models of VSL are tested SNe data-sets with proper constraints on the model parameters. The comparison of the three models and flat ΛCDM in distance modulus is showed. Some basic problems and the difficulties of the confirmation of the VSL theory are also discussed.

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