scholarly journals Observational constraints on the generalized α attractor model

2018 ◽  
Vol 27 (05) ◽  
pp. 1850058 ◽  
Author(s):  
M. Shahalam ◽  
Ratbay Myrzakulov ◽  
Shynaray Myrzakul ◽  
Anzhong Wang
Keyword(s):  
Cosmic Acceleration ◽  
Asymptotic Region ◽  
Model Parameters ◽  
Observational Constraints ◽  
Late Time ◽  
Freezing And Thawing ◽  
Energy Models ◽  
Slow Roll ◽  
Attractor Model ◽  
Original Potential

We study the generalized [Formula: see text] attractor model in the context of the late time cosmic acceleration. The model interpolates between the scaling freezing and thawing dark energy models. In the slow roll region, the original potential is modified whereas the modification ceases in the asymptotic region and the effective potential behaves as the quadratic one. In our setting, the field rolls slowly around the present epoch and mimics the scaling behavior in the future. We obtain observational constraints on the model parameters by using an integrated database (SN+Hubble+BAO+CMB).

scholarly journals An accelerating cosmological model from a parametrization of Hubble parameter

2019 ◽  
Vol 35 (05) ◽  
pp. 2050011 ◽  
Author(s):  
S. K. J. Pacif ◽  
Md Salahuddin Khan ◽  
L. K. Paikroy ◽  
Shalini Singh
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Hubble Parameter ◽  
Cosmological Parameters ◽  
Cosmic Time ◽  
Solution Procedure ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Late Time ◽  
Field Equations

In view of late-time cosmic acceleration, a dark energy cosmological model is revisited wherein Einstein’s cosmological constant is considered as a candidate of dark energy. Exact solution of Einstein field equations (EFEs) is derived in a homogeneous isotropic background in classical general relativity. The solution procedure is adopted in a model-independent way (or the cosmological parametrization). A simple parametrization of the Hubble parameter (H) as a function of cosmic time t is considered which yields an exponential type of evolution of the scale factor (a) and also shows a negative value of deceleration parameter at the present time with a signature flip from early deceleration to late acceleration. Cosmological dynamics of the model obtained have been discussed illustratively for different phases of the evolution of the universe. The evolution of different cosmological parameters is shown graphically for flat and closed cases of Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime for the presented model (open case is incompatible to the present scenario). We have also constrained our model parameters with the updated (36 points) observational Hubble dataset.

scholarly journals Cosmic acceleration from coupling of baryonic and dark matter components: Analysis and diagnostics

2019 ◽  
Vol 28 (06) ◽  
pp. 1950083 ◽  
Author(s):  
Abhineet Agarwal ◽  
R. Myrzakulov ◽  
S. K. J. Pacif ◽  
M. Shahalam
Keyword(s):  
Dark Matter ◽  
Degrees Of Freedom ◽  
Cosmic Acceleration ◽  
Jordan Frame ◽  
Model Parameters ◽  
Late Time ◽  
Baryonic Matter ◽  
Acoustic Oscillations ◽  
Type Ia ◽  
Components Analysis

In this paper, we examine a scenario in which late-time cosmic acceleration might arise due to the coupling between baryonic matter and dark matter without the presence of extra degrees of freedom. In this case, one can obtain late-time acceleration in Jordan frame and not in Einstein frame. We consider two different forms of parametrization of the coupling function, and put constraints on the model parameters by using an integrated dataset of Hubble parameter, Type Ia supernova and baryon acoustic oscillations. The models under consideration are consistent with the observations. In addition, we perform the statefinder and [Formula: see text] diagnostics, and show that the models exhibit a distinctive behavior due to the phantom characteristic in future which is a generic feature of the underlying scenario.

scholarly journals Induced gravity effect on inflationary parameters in a holographic cosmology

2020 ◽  
Vol 29 (02) ◽  
pp. 2050010 ◽  
Author(s):  
Aatifa Bargach ◽  
Farida Bargach ◽  
Ahmed Errahmani ◽  
Taoufik Ouali
Keyword(s):  
Model Parameters ◽  
Observational Constraints ◽  
Tachyon Field ◽  
Exponential Potential ◽  
Quadratic Potential ◽  
Induced Gravity ◽  
Slow Roll ◽  
Inflationary Parameters ◽  
Correction Terms ◽  
Good Agreement

We investigate the observational constraints on inflationary parameters in the context of a holographic cosmology with an induced gravity correction. We consider two situations where a universe is first filled with a scalar field and second with a tachyon field. Both cases are investigated in a slow-roll regime. We adopt a quadratic potential and an exponential potential for the scalar and the tachyon inflation, respectively. In this regard, the standard background and perturbative parameters characterizing the inflationary era are modified by correction terms. We show a good agreement between theoretical model parameters and Planck2018 observational data for both scalar and tachyon fields.

scholarly journals Dark energy in Horndeski theories after GW170817: A review

2019 ◽  
Vol 28 (05) ◽  
pp. 1942005 ◽  
Author(s):  
Ryotaro Kase ◽  
Shinji Tsujikawa
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Equations Of Motion ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Dark Energy Density ◽  
Static Approximation ◽  
Binary Neutron Star ◽  
Energy Models ◽  
Gravitational Theories

The gravitational wave (GW) event GW170817 from a binary neutron star merger together with the electromagnetic counterpart showed that the speed of GWs [Formula: see text] is very close to that of light for the redshift [Formula: see text]. This places tight constraints on dark energy models constructed in the framework of modified gravitational theories. We review models of the late-time cosmic acceleration in scalar–tensor theories with second-order equations of motion (dubbed Horndeski theories) by paying particular attention to the evolution of dark energy equation of state and observables relevant to the cosmic growth history. We provide a gauge-ready formulation of scalar perturbations in full Horndeski theories and estimate observables associated with the evolution of large-scale structures, cosmic microwave background and weak lensing by employing a so-called quasi-static approximation for the modes deep inside the sound horizon. In light of the recent observational bound of [Formula: see text], we also classify surviving dark energy models into four classes depending on different structure-formation patterns and discuss how they can be observationally distinguished from each other. In particular, the nonminimally coupled theories in which the scalar field [Formula: see text] has a coupling with the Ricci scalar [Formula: see text] of the form [Formula: see text], including [Formula: see text] gravity, can be tightly constrained not only from the cosmic expansion and growth histories but also from the variation of screened gravitational couplings. The cross-correlation of integrated Sachs–Wolfe signal with galaxy distributions can be a key observable for placing bounds on the relative ratio of cubic Galileon density to total dark energy density. The dawn of GW astronomy will open up a new window to constrain nonminimally coupled theories further by the modified luminosity distance of tensor perturbations.

scholarly journals Cosmic acceleration sourced by modification of gravity without extra degrees of freedom

2019 ◽  
Vol 16 (08) ◽  
pp. 1950128
Author(s):  
Abhineet Agarwal ◽  
R. Myrzakulov ◽  
S. K. J. Pacif ◽  
M. Sami ◽  
Anzhong Wang
Keyword(s):  
Degrees Of Freedom ◽  
Large Scale ◽  
Cosmic Acceleration ◽  
Jordan Frame ◽  
Model Parameters ◽  
Late Time ◽  
Baryonic Matter ◽  
Narrow Region ◽  
Cluster Data ◽  
Age Constraints

In this paper, we investigate a scenario in which late-time cosmic acceleration might arise due to coupling between dark matter and baryonic matter without resorting to dark energy or large-scale modification of gravity associated with extra degrees of freedom. The scenario can give rise to late-time acceleration in Jordan frame and no acceleration in Einstein frame — generic modification of gravity caused by disformal coupling. Using a simple parametrization of the coupling function, in maximally disformal case, we constrain the model parameters by using the age constraints due to globular cluster data. We also obtain observational constraints on the parameters using [Formula: see text] datasets. In this case, we distinguish between phantom and non-phantom acceleration and show that the model can give rise to phantom behavior in a narrow region of parameter space.

scholarly journals Quintessence and Holographic Dark Energy infTGravity

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
M. Zubair
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Energy Model ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Efficient Tool ◽  
Future Evolution ◽  
Energy Models

We regardfTtheory as an efficient tool to explain the current cosmic acceleration and associate its evolution with the known dark energy models. The numerical scheme is applied to reconstructfTtheory from dark energy model with constant equation of state parameter and holographic dark energy model. We set the model parametersωϑandcas describing the different evolution eras and show the distinctive behavior of each case realized infTtheory. We also present the future evolution of reconstructedfTand find that it is consistent with the recent observations.

scholarly journals Reconstruction of cosmic history from a simple parametrization of H

2017 ◽  
Vol 14 (07) ◽  
pp. 1750111 ◽  
Author(s):  
Shibesh Kumar Jas Pacif ◽  
Ratbay Myrzakulov ◽  
Shynaray Myrzakul
Keyword(s):  
Hubble Parameter ◽  
Functional Form ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Late Time ◽  
Text Data ◽  
Simple Modification ◽  
Big Rip ◽  
Cosmic History

In this paper, we propose a simple parametrization of the Hubble parameter (HP) [Formula: see text] in order to explain the late-time cosmic acceleration. We show that our proposal covers many models obtained in different schemes of parametrization under one umbrella. We demonstrate that a simple modification in the functional form of HP can give rise to interesting cosmological phenomena such as big rip singularity, bounce and others. We have also constrained the model parameters using the latest 28 points of [Formula: see text] data for three cases which admit transition from deceleration to acceleration.

RECENT STATUS OF DARK ENERGY

2010 ◽  
Vol 25 (11n12) ◽  
pp. 843-858 ◽  
Author(s):  
SHINJI TSUJIKAWA
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Chaplygin Gas ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Energy Models ◽  
Local Gravity ◽  
Dynamical Dark Energy

We review a number of approaches that have been adopted to explain the origin of dark energy responsible for the late-time cosmic acceleration. This includes the cosmological constant and dynamical dark energy models such as quintessence, k -essence, Chaplygin gas, f(R) gravity, scalar-tensor theories, and braneworld models. We also discuss observational and local gravity constraints on those models and clarify which models are favored or ruled out in current observations.

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