scholarly journals The models of transit cosmology along with observational constriction in f(Q,T) gravity

2021 ◽  
pp. 2150159
Author(s):  
Anirudh Pradhan ◽  
Archana Dixit
Keyword(s):  
Equation Of State ◽  
Deceleration Parameter ◽  
Transition Point ◽  
Energy Momentum Tensor ◽  
Cosmological Parameters ◽  
Momentum Tensor ◽  
Curve Analysis ◽  
Model Parameters ◽  
Data Sets ◽  
Light Curve Analysis

Xu et al. (Eur. Phys. J. C 79 (2019) 708) have anticipated the theory of Gravity. The modified study of [Formula: see text] is elucidated here as Cosmological model. In it the action holds a role as a capricious arbitrary function [Formula: see text]. At this juncture [Formula: see text] functions as non-metricity and for matter fluid, [Formula: see text] outlines as energy-momentum tensor. The function [Formula: see text] quadratic in [Formula: see text] and linear in [Formula: see text] as [Formula: see text] has been taken as our research in which [Formula: see text], [Formula: see text] and [Formula: see text] stand as model parameters, induced by [Formula: see text] gravity. A range of cosmological parameters have been attained by us such as in Universe viz. Hubble parameter [Formula: see text], Friedmann–Lemaitre–Robertson–Walker (FLRW), deceleration parameter [Formula: see text], etc. in terms of scale-factor and in terms of redshift [Formula: see text] by confining to the law of energy-conservation. The fittest values of the model parameters have been acquired by us as the observational constrictions on the model, by utilizing the accessible data sets like Hubble data sets [Formula: see text], union 2.1 compilation of SNe Ia data sets and Joint Light Curve Analysis (JLA) data sets. We have applied [Formula: see text]-test formula. The values of various observational parameters have been premeditated by us viz. [Formula: see text], [Formula: see text], [Formula: see text] and state finder parameters [Formula: see text]. They are absolutely very close to the standard cosmological models. It has also been observed by us that the deceleration parameter [Formula: see text] exhibits signature-flipping (transition) point within the range [Formula: see text]. It is observed that it changes its phase from decelerated to accelerated expanding universe with equation of state (EoS) [Formula: see text] for [Formula: see text].

scholarly journals Matter perturbations in Einstein dark energy model

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Zahra Haghani
Keyword(s):  
Dark Energy ◽  
Fixed Points ◽  
Dark Energy Model ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Data Sets ◽  
Independent Data ◽  
De Sitter ◽  
Energy Theory

AbstractWe consider the growth rate of matter perturbations in the Einstein dark energy theory. The theory consists of the Einstein–Hilbert Lagrangian plus the trace of the energy momentum tensor, coupled non-minimally to a dynamical vector field. We will show that the theory has three fixed points corresponding to the dust, radiation and de Sitter universes. Due to the present of trace of the energy–momentum tensor in the Lagrangian, the fixed points occurs in different locations compared to $$\Lambda $$ Λ CDM theory. We will analyze the theory with and without cosmological constant. We will fit the model parameters using two independent data sets corresponding to the Hubble parameter H and also $$f\sigma _8$$ f σ 8 . The theory is then shown to be consistent with observational data.

Dark energy nature of viscus universe in f(Q)-gravity with observational constraints

2021 ◽  
pp. 2150124
Author(s):  
Anirudh Pradhan ◽  
Dinesh Chandra Maurya ◽  
Archana Dixit
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Scale Factor ◽  
Model Parameters ◽  
Data Sets ◽  
Field Equations ◽  
Normal Matter ◽  
Energy Behavior

In this study, we have investigated the dark energy behavior of the viscus-fluid in [Formula: see text]-gravity in a flat, isotropic and homogeneous Friedmann–Lemaitre–Robertson–Walker (FLRW) space-time metric. We have considered the linear form of [Formula: see text] function as [Formula: see text] with [Formula: see text] and [Formula: see text] as model parameters. We have solved the field equations for the scale factor [Formula: see text] and found [Formula: see text], where [Formula: see text] and [Formula: see text] and [Formula: see text] is an integrating constant, [Formula: see text] is the EoS for normal matter and [Formula: see text] is generated from bulk-viscus fluid. We have calculated the several cosmological parameters for this scale factor and studied their physical and geometrical behavior along the observational data sets [Formula: see text] and Union [Formula: see text] compilation of SNe Ia data sets. We have observed that the [Formula: see text] factor reveals the presence of cosmological constant and for [Formula: see text], the acceleration drives by the bulk-viscosity of the fluid and it behaves just like dark energy model without cosmological constant. We have studied the effective EoS [Formula: see text] and found [Formula: see text]. We have evaluated the age of the present universe as [Formula: see text] Gyrs. and also, we have studied the nature of deceleration parameter with the signature-flipping point at [Formula: see text] and the present value of deceleration parameter [Formula: see text] is obtained as [Formula: see text].

Cosmological models in R2 gravity with hybrid expansion law

2021 ◽  
pp. 2150143
Author(s):  
Partha Sarathi Debnath ◽  
Bikash Chandra Paul
Keyword(s):  
Equation Of State ◽  
Deceleration Parameter ◽  
State Parameter ◽  
Cosmological Models ◽  
Model Parameters ◽  
Density Parameter ◽  
Eos Parameter ◽  
Data Set ◽  
Deceleration Phase ◽  
Higher Derivative

In this paper, evolution of a Friedmann–Robertson–Walker universe is studied in a higher derivative theory of gravity. The relativistic solutions admitting hybrid expansion law of the universe are explored here. Hybrid expansion law is a general form of scale factor from which one can recover both the power-law expansion and exponential expansion as a special case. The hybrid expansion law is interesting as it addresses the early deceleration phase and presents accelerating phase satisfactorily. It is found that an inflationary scenario with hybrid expansion law is permitted in the [Formula: see text] gravity fairly well. We consider universe filled with cosmic fluid that describes by an equation of state (EoS) parameter which varies with time. Consequently, we analyze the time variation of energy density parameter, cosmic pressure, equation of state parameter, deceleration parameter and jerk parameter in the cosmological model. The constraints of the model parameters imposed by the cosmological observational data set are determined. The present value of the deceleration parameter [Formula: see text], EoS parameter and the epoch at which the transition of decelerated phase to accelerated phase are estimated. In the higher derivative theory, we obtain some new and interesting cosmological solutions relevant for building cosmological models.

scholarly journals Analysis off(R)Theory Corresponding to NADE and NHDE

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
M. Sharif ◽  
M. Zubair
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Future Evolution ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Effective Description

We develop the connection off(R)theory with new agegraphic and holographic dark energy models. The functionf(R)is reconstructed regarding thef(R)theory as an effective description for these dark energy models. We show the future evolution offand conclude that these functions represent distinct pictures of cosmological eras. The cosmological parameters such as equation of state parameter, deceleration parameter, statefinder diagnostic, andw−w′analysis are investigated which assure the evolutionary paradigm off.

scholarly journals THE EFFECT OF DIFFERENT OBSERVATIONAL DATA IN CONSTRAINING COSMOLOGICAL PARAMETERS

2012 ◽  
Vol 10 ◽  
pp. 85-94 ◽  
Author(s):  
YUNGUI GONG ◽  
QING GAO ◽  
ZONG-HONG ZHU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Observational Data ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Model Parameters ◽  
Type Ia Supernova ◽  
Equation Of State Parameter ◽  
Type Ia

We use the SNLS3 compilation of 472 type Ia supernova data, the baryon acoustic oscillation measurement of distance, and the cosmic microwave background radiation data from the seven year Wilkinson Microwave Anisotropy Probe to study the effect of their different combinations on the fittings of cosmological parameters. Neither BAO nor WMAP7 data alone gives good constraint on the equation of state parameter of dark energy, but both WMAP7 data and BAO data help type Ia supernova data break the degeneracies among the model parameters, hence tighten the constraint on the variation of equation of state parameter wa, and WMAP7 data does the job a little better. Although BAO and WMAP7 data provide reasonably good constraints on Ωm and Ωk, it is not able to constrain the dynamics of dark energy, we need SNe Ia data to probe the property of dark energy, especially the variation of the equation of state parameter of dark energy. For the SNLS SNe Ia data, the nuisance parameters α and β are consistent for all different combinations of the above data. Their impacts on the fittings of cosmological parameters are minimal. ΛCDM model is consistent with current observational data.

scholarly journals Dynamics of an Anisotropic Universe inf(R,T)Theory

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
B. Mishra ◽  
Sankarsan Tarai ◽  
S. K. Tripathy
Keyword(s):  
Power Law ◽  
Modified Gravity ◽  
Bianchi Type ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Anisotropic Universe ◽  
Expansion Of The Universe ◽  
Physical Features ◽  
The Universe

Dynamics of an anisotropic universe is studied inf(R,T)gravity using a rescaled functionalf(R,T), whereRis the Ricci Scalar andTis the trace of energy-momentum tensor. Three models have been constructed assuming a power law expansion of the universe. Physical features of the models are discussed. The model parameters are constrained from a dimensional analysis. It is found from the work that the anisotropic Bianchi typeVIh(BVIh) model in the modified gravity generally favours a quintessence phase when the parameterhis either-1or0. We may not get viable models in conformity with the present day observation forh=1.

scholarly journals Equation of state in (2+1)-flavor QCD at physical point with improved Wilson fermion action using gradient flow

2018 ◽  
Vol 175 ◽  
pp. 07023 ◽  
Author(s):  
Kazuyuki Kanaya ◽  
Shinji Ejiri ◽  
Ryo Iwami ◽  
Masakiyo Kitazawa ◽  
Hiroshi Suzuki ◽  
...  
Keyword(s):  
Equation Of State ◽  
Quark Mass ◽  
Energy Momentum Tensor ◽  
Gradient Flow ◽  
Chiral Condensate ◽  
Momentum Tensor ◽  
Mass Point ◽  
Physical Point ◽  
Preliminary Results ◽  
Fermion Action

We study the energy-momentum tensor and the equation of state as well as the chiral condensate in (2+1)-flavor QCD at the physical point applying the method of Makino and Suzuki based on the gradient flow. We adopt a nonperturbatively O(a)- improved Wilson quark action and the renormalization group-improved Iwasaki gauge action. At Lattice 2016, we have presented our preliminary results of our study in (2+1)- flavor QCD at a heavy u; d quark mass point. We now extend the study to the physical point and perform finite-temperature simulations in the range T ≃ 155.544 MeV (Nt = 4-14 including odd Nt’s) at a ≃ 0:09 fm. We show our final results of the heavy QCD study and present some preliminary results obtained at the physical point so far.

scholarly journals Anisotropic cosmological models in f(R,T) gravity with variable deceleration parameter

2017 ◽  
Vol 14 (06) ◽  
pp. 1750097 ◽  
Author(s):  
Pradyumn Kumar Sahoo ◽  
Parbati Sahoo ◽  
Binaya Kumar Bishi
Keyword(s):  
Bulk Viscosity ◽  
Deceleration Parameter ◽  
Momentum Tensor ◽  
Matter Content ◽  
Accelerating Universe ◽  
Data Sets ◽  
Type I ◽  
Field Equations ◽  
Future Evolution ◽  
The Universe

The objective of this work enclosed with the study of spatially homogeneous anisotropic Bianchi type-I universe in [Formula: see text] gravity (where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of stress energy momentum tensor) in two different cases viz. [Formula: see text] and [Formula: see text] with bulk viscosity matter content. In this study, we consider a time varying deceleration parameter (DP), which generates an accelerating universe to obtain the exact solution of the field equations. The physical and kinematical properties of both the models are discussed in detail for the future evolution of the universe. We have explored the nature of WEC, DEC, SEC and energy density for both the cases. We have found that both the models, with bulk viscosity matter component, show an acceleration of the universe. We have also shown that the cosmic jerk parameter is compatible with the three kinematical data sets.

scholarly journals Reconstruction of interaction rate in holographic dark energy model with Hubble horizon as the infrared cut-off

2017 ◽  
Vol 26 (11) ◽  
pp. 1750136 ◽  
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Energy Equation ◽  
Present Model ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Model Parameters ◽  
Interaction Rate ◽  
Equation Of State Parameter

This work is the reconstruction of the interaction rate of holographic dark energy whose infrared cut-off scale is set by the Hubble length. We have reconstructed the interaction rate between dark matter and the holographic dark energy for a specific parameterization of the effective equation-of-state parameter. We have obtained observational constraints on the model parameters using the latest type Ia supernova (SNIa), baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) radiation datasets. We have found that for the present model, the interaction rate increases with expansion and remains positive throughout the evolution. For a comprehensive analysis, we have also compared the reconstructed results of the interaction rate with other well-known holographic dark energy models. The nature of the deceleration parameter, the statefinder parameters and the dark energy equation-of-state parameter have also been studied for the present model. It has been found that the deceleration parameter favors the past decelerated and recent accelerated expansion phase of the universe. It has also been found that the dark energy equation-of-state parameter shows a phantom nature at the present epoch.

A study of pilgrim dark energy model in Brans–Dicke theory

2019 ◽  
Vol 34 (12) ◽  
pp. 1950083
Author(s):  
M. Sharif ◽  
Syed Asif Ali Shah
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Statefinder Parameters ◽  
Future Event ◽  
Pilgrim Dark Energy ◽  
Frw Model ◽  
Future Event Horizon

In this paper, we study the behavior of non-interacting and interacting pilgrim dark energy (DE) for non-flat FRW model in Brans–Dicke (BD) theory. We consider the future event horizon as well as logarithmic form of BD scalar field [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] is the scale factor. We evaluate some well-known cosmological parameters such as equation of state as well as deceleration parameter and [Formula: see text] plane as well as statefinder parameters. We discuss graphical behavior of these parameters through pilgrim DE parameter [Formula: see text] for both non-interacting as well as interacting case with interacting parameter [Formula: see text]. It is found that the equation of state parameter gives consistent results with the current cosmic behavior while the deceleration parameter represents transition from decelerated to accelerated phase. The cosmological planes represent different DE regions. Finally, we discuss stability of the model through squared speed of sound in both cases.

Sign in / Sign up

Export Citation Format

Share Document