scholarly journals Modified holographic energy density-driven inflation and some cosmological outcomes

2020 ◽  
Vol 17 (05) ◽  
pp. 2050066
Author(s):  
Gargee Chakraborty ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Bulk Viscosity ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Late Time ◽  
Effective Equation ◽  
Inflationary Scenario ◽  
Acceleration Of The Universe ◽  
The Universe

Motivated by the work of Nojiri et al. [S. Nojiri, S. D. Odintsov and E. N. Saridakis, Holographic inflation, Phys. Lett. B 797 (2019) 134829], this study reports a model of inflation under the consideration that the inflationary regime is originated by a type of holographic energy density. The infrared cutoff has been selected based on the modified holographic model that is a particular case of Nojiri–Odintsov holographic dark energy [S. Nojiri and S. D. Odintsov, Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285] that unifies phantom inflation with the acceleration of the universe on late time. On getting an analytical solution for Hubble parameter we considered the presence of bulk viscosity and the effective equation of state parameter appeared to be consistent with inflationary scenario with some constraints. It has also being observed that in the inflationary scenario the contribution of bulk viscosity is not of much significance and its influence is increasing with the evolution of the universe. Inflationary observables have been computed for the model and the slow-roll parameters have been computed. Finally, it has been observed that the trajectories in [Formula: see text] are compatible with the observational bound found by Planck. It has been concluded that the tensor to scalar ratio for this model can explain the primordial fluctuation in the early universe as well.

Cosmology of viscous holographic f(G) gravity and consequences in the framework of quintessence scalar field

2019 ◽  
Vol 16 (11) ◽  
pp. 1950176
Author(s):  
Swati Sinha ◽  
Surajit Chattopadhyay ◽  
Irina Radinschi
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Holographic Dark Energy ◽  
Inhomogeneous Equation ◽  
Late Time ◽  
Effective Equation ◽  
Future Singularity ◽  
Warm Inflation ◽  
The Universe

Work reported in this study demonstrates the reconstruction schemes for the [Formula: see text] gravity in the framework of bulk viscosity and holographic background evolution by considering the universe filled by the viscous fluid that is just special class of more general fluids as described in Nojiri and Odintsov [Inhomogeneous equation of state of the universe: Phantom era, future singularity, and crossing the phantom barrier, Phys. Rev. D 72 (2005) 023003]. The bulk viscous pressure has been considered as [Formula: see text], with [Formula: see text]. Considering the scale factor in power law form and taking holographic dark energy (HDE) with density [Formula: see text] and generalized extended holographic dark energy (EGHRDE) with density [Formula: see text], a specific case of Nojiri–Odintsov holographic DE ([Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285]) we have derived solutions for [Formula: see text] and the subsequent effective equation of state parameters have been found to behave like quintom irrespective of the choice of [Formula: see text]. Finally, considering [Formula: see text] as quintessence scalar field we have explored the possibility of quasi-exponential expansion and warm inflation.

scholarly journals Accelerating cosmology in modified gravity: From convenient F(R) or string-inspired theory to bimetric F(R) gravity

2014 ◽  
Vol 11 (02) ◽  
pp. 1460006 ◽  
Author(s):  
Shin'ichi Nojiri ◽  
Sergei D. Odintsov
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Early Time ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Reconstruction Method ◽  
Free Theory ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Unified Description

We consider modified gravity which may describe the early-time inflation and/or late-time cosmic acceleration of the universe. In particular, we discuss the properties of F(R), F(G), string-inspired and scalar-Einstein–Gauss–Bonnet gravities, including their FRW equations and fluid or scalar-tensor description. Simplest accelerating cosmologies are investigated and possibility of unified description of the inflation with dark energy is described. The cosmological reconstruction program which permits to get the requested universe evolution from modified gravity is developed. As some extension, massive F(R) bigravity which is ghost-free theory is presented. Its scalar-tensor form turns out to be the easiest formulation. The cosmological reconstruction method for such bigravity is presented. The unified description of inflation with dark energy in F(R) bigravity turns out to be possible.

scholarly journals CAN BRANS–DICKE SCALAR FIELD ACCOUNT FOR DARK ENERGY AND DARK MATTER?

2006 ◽  
Vol 21 (15) ◽  
pp. 1241-1248 ◽  
Author(s):  
M. ARIK ◽  
M. C. ÇALIK
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Late Time ◽  
Energy Contribution ◽  
Time Solution ◽  
The Universe

By using a linearized non-vacuum late time solution in Brans–Dicke cosmology, we account for the 75% dark energy contribution but not for approximately 23% dark matter contribution to the present day energy density of the universe.

scholarly journals PRESENT ACCELERATION OF THE UNIVERSE, HOLOGRAPHIC ENERGY AND BRANS–DICKE THEORY

2009 ◽  
Vol 24 (22) ◽  
pp. 1785-1792 ◽  
Author(s):  
B. NAYAK ◽  
L. P. SINGH
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Accelerated Expansion ◽  
Temporal Behavior ◽  
Holographic Dark Energy Model ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe

The present-day accelerated expansion of the universe is naturally addressed within the Brans–Dicke theory just by using holographic dark energy model with inverse of Hubble scale as IR cutoff and power law temporal behavior of scale factor. It is also concluded that if the universe continues to expand, then one day it might be completely filled with dark energy.

scholarly journals DARK ENERGY IN PRACTICE

2010 ◽  
Vol 25 (29) ◽  
pp. 5253-5331 ◽  
Author(s):  
DOMENICO SAPONE
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Complete List ◽  
Late Time ◽  
Evolution Of The Universe ◽  
Late Time Acceleration ◽  
Energy Models ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Alternative Theories

In this paper we review a part of the approaches that have been considered to explain the extraordinary discovery of the late time acceleration of the Universe. We discuss the arguments that have led physicists and astronomers to accept dark energy as the current preferable candidate to explain the acceleration. We highlight the problems and the attempts to overcome the difficulties related to such a component. We also consider alternative theories capable of explaining the acceleration of the Universe, such as modification of gravity. We compare the two approaches and point out the observational consequences, reaching the sad but foresightful conclusion that we will not be able to distinguish between a Universe filled by dark energy or a Universe where gravity is different from General Relativity. We review the present observations and discuss the future experiments that will help us to learn more about our Universe. This is not intended to be a complete list of all the dark energy models but this paper should be seen as a review on the phenomena responsible for the acceleration. Moreover, in a landscape of hardly compelling theories, it is an important task to build simple measurable parameters useful for future experiments that will help us to understand more about the evolution of the Universe.

A study on the modified holographic Ricci dark energy in logarithmic f(T) gravity

2013 ◽  
Vol 91 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Modified Gravity ◽  
State Parameter ◽  
Ricci Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Universe

In this paper, we have studied and investigated the behavior of a modified holographic Ricci dark energy (DE) model interacting with pressureless dark matter (DM) under the theory of modified gravity, dubbed logarithmic f(T) gravity. We have chosen the interaction term between DE and DM in the form Q = 3γHρm and investigated the behavior of the torsion, T, the Hubble parameter, H, the equation of state parameter, ωDE, the energy density of DE, ρDE, and the energy density contribution due to torsion, ρT, as functions of the redshift, z. We have found that T increases with the redshift, z, H increases with the evolution of the universe, ωDE has a quintessence-like behavior, and both energy densities increase going from higher to lower redshifts.

scholarly journals On a Slightly Different Power Law-Scaling for the Flat Universe

2020 ◽  
Vol 12 (4) ◽  
pp. 569-574
Author(s):  
C. Sivakumar ◽  
R. Francis
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Power Law ◽  
Hubble Parameter ◽  
State Parameter ◽  
Effective Equation ◽  
Flat Universe ◽  
Equation Of State Parameter ◽  
Age Of The Universe ◽  
The Universe

A slightly different power law-scaling fits to the picture of our 13.7 billion years old flat universe which is expanding presently at 67 km/s/Mpc with an acceleration. The model which is an attempt to retain power-law scaling in the light of the accepted facts about the universe we are living in, has a constant effective equation of state parameter as the cosmic fluid is a solution of matter, radiation and dark energy. It is successful in explaining the acceleration of universe which the normal power law fails if the present Hubble parameter is 67 km/s/Mpc and age of the universe is 13.7 billion years, and it is free from the defect of singularity.

scholarly journals Anisotropic Universe with Manimally Interacting Matter and Holographic Dark Energy

2021 ◽  
Vol 42 (1) ◽  
pp. 39-57
Author(s):  
Mohammad Moksud Alam
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Anisotropic Universe ◽  
Tensor Theory ◽  
Exponential Expansion ◽  
Recent Phase ◽  
Theory Of Gravitation ◽  
Expansion Model ◽  
The Universe

The holographic dark energy (HDE), a form of dark energy, has been a useful tool in explaining the recent phase transition of the universe. In this paper, we study the anisotropic and homogeneous Bianchi type-III model of the universe filled with minimally interacting matter and holographic dark energy under the framework of the Brans-Dicke (BD) scalar tensor theory of gravitation. Considering two physically plausible conditions such as, (i) the special law of variation for Hubble parameter and (ii) the scalar expansion proportional to the shear scalar, we propose two new models namely, exponential expansion model and power law expansion model. We also show the dynamics of these models fit with existing observational data and literature thereof. The transit behavior of the equation of state parameter for dark energy has been analyzed graphically. The jerk parameter is also studied for both of the models describing cosmological evolution. The Chittagong Univ. J. Sci. 42(1): 39-57, 2020

scholarly journals Sign-changeable interacting agegraphic dark energy in Brans–Dicke cosmology

2020 ◽  
Vol 98 (7) ◽  
pp. 643-649
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
The State ◽  
Evolutionary Equation ◽  
Model Parameters ◽  
Late Time ◽  
Frw Universe ◽  
Agegraphic Dark Energy ◽  
Deceleration Phase ◽  
The Universe

We explore a spatially homogeneous and isotropic Friedmann–Robertson–Walker (FRW) universe that is filled with agegraphic dark energy (ADE) with mutual interaction with pressureless dark matter in the background of Brans–Dicke (BD) theory. We consider both original and a new type of ADE (NADE) and further assume that the sign of the interaction term can change during the history of the universe. We obtain the equation of the state parameter, the deceleration parameter, and the evolutionary equation for the sign-changeable interacting ADE and NADE in BD cosmology. We find that in both models, the equation of the state parameter, wD, cannot cross the phantom line, although they can predict the universe evolution from the early deceleration phase to the late time acceleration, compatible with observations. We also investigate the sound stability of these models and find out that both models cannot show a signal of stability for different model parameters.

scholarly journals DIRECT DETERMINATIONS OF THE REDSHIFT BEHAVIOR OF THE PRESSURE, ENERGY DENSITY, AND EQUATION OF STATE OF THE DARK ENERGY AND THE ACCELERATION OF THE UNIVERSE

2005 ◽  
Vol 20 (06) ◽  
pp. 1113-1120 ◽  
Author(s):  
RUTH A. DALY ◽  
S. G. DJORGOVSKI
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Radio Galaxy ◽  
A Priori ◽  
Acceleration Rate ◽  
Acceleration Of The Universe ◽  
Theory Of Gravity ◽  
The Universe

One of the goals of current cosmological studies is the determination of the expansion and acceleration rates of the universe as functions of redshift, and the determination of the properties of the dark energy that can explain these observations. Here the expansion and acceleration rates are determined directly from the data, without the need for the specification of a theory of gravity, and without adopting an a priori parameterization of the form or redshift evolution of the dark energy. We use the latest set of distances to SN standard candles from Riess et al. (2004), supplemented by data on radio galaxy standard ruler sizes, as described by Daly & Djorgovski (2003, 2004). We find that the universe transitions from acceleration to deceleration at a redshift of zT≈0.4, with the present value of q0=-0.35±0.15. The standard "concordance model" with Ω0=0.3 and Λ=0.7 provides a reasonably good fit to the dimensionless expansion rate as a function of redshift, though it fits the dimensionless acceleration rate as a function of redshift less well. The expansion and acceleration rates are then combined with a theory of gravity to determine the pressure, energy density, and equation of state of the dark energy as functions of redshift. Adopting General Relativity as the correct theory of gravity, the redshift trends for the pressure, energy density, and equation of state of the dark energy out to z~1 are determined, and are found to be generally consistent with the concordance model; they have zero redshift values of p0=-0.6±0.15, f0=0.62±0.05, and w0=-0.9±0.1.

Sign in / Sign up

Export Citation Format

Share Document