scholarly journals Jointly modelling Cosmic Inflation and Dark Energy

2021 ◽  
Vol 2105 (1) ◽  
pp. 012001
Author(s):  
Konstantinos Dimopoulos
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Modified Gravity ◽  
Cosmic Inflation

Abstract Quintessential inflation utilises a single scalar field to account for the observations of both cosmic inflation and dark energy. The requirements for modelling quintessential inflation are described and two explicit successful models are presented in the context of α-attractors and Palatini modified gravity.

scholarly journals 1D Supergravity FLRW Model of Starobinsky

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 449
Author(s):  
Nephtalí E. Martínez-Pérez ◽  
Cupatitzio Ramírez-Romero ◽  
Víctor M. Vázquez-Báez
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy State ◽  
Hamiltonian Formulation ◽  
Low Energy ◽  
The Other ◽  
Classical Dynamics ◽  
Massive Scalar ◽  
Massive Scalar Field ◽  
Cosmic Inflation

We study two homogeneous supersymmetric extensions for the f(R) modified gravity model of Starobinsky with the FLRW metric. The actions are defined in terms of a superfield R that contains the FLRW scalar curvature. One model has N = 1 local supersymmetry, and its bosonic sector is the Starobinsky action; the other action has N = 2, its bosonic sector contains, in additional to Starobinsky, a massive scalar field without self-interaction. As expected, the bosonic sectors of these models are consistent with cosmic inflation, as we show by solving numerically the classical dynamics. Inflation is driven by the R2 term during the large curvature regime. In the N = 2 case, the additional scalar field remains in a low energy state during inflation. Further, by means of an additional superfield, we write equivalent tensor-scalar-like actions from which we can give the Hamiltonian formulation.

A study of the bulk viscous pressure in scalar fields and holographic Ricci dark energy considered in the modified gravity framework

2020 ◽  
Vol 98 (7) ◽  
pp. 664-674 ◽  
Author(s):  
Sthiti Chakrabarti ◽  
Surajit Chattopadhyay ◽  
Irina Radinschi
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Bulk Viscosity ◽  
Modified Gravity ◽  
Scalar Fields ◽  
Effective Equation ◽  
Ricci Dark Energy ◽  
Scalar Field Models ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

The work presented in this paper reports a rigorous study of the reconstruction of the modified gravity in the framework of the scalar field models of dark energy and holographic Ricci dark energy, a generalized version of the holographic dark energy presented in S. Nojiri and S.D. Odintsov. Gen. Relativ. Gravitation, 38, 1285 (2006). The tachyon and quintessence scalar fields have been considered and the cosmology associated with the presence of bulk viscosity has been studied. In the first part of our study, we have demonstrated the behaviour of the bulk viscosity coefficient in the framework of the reconstructed tachyon scalar field model of dark energy. The scale factor is chosen in the form a(t) = a0tβ, where β > 0. Two scalar field models, namely, tachyon and quintessence, have been considered in the framework of the modified field equations through incorporation of the bulk viscous pressure. The reconstructed density and pressure of the scalar field models have been explored for the cosmological consequences in the presence of bulk viscosity. The behaviour of the effective equation of state parameters has been investigated. Finally, we have reconstructed f(T) gravity in the presence of holographic Ricci dark energy and a transition of the effective equation of state parameter from quintessence to phantom has been observed.

Cosmology of Tsallis holographic scalar field models in Chern–Simons modified gravity and optimization of model parameters through χ2 minimization

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Gargee Chakraborty ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Modified Gravity ◽  
Hubble Parameter ◽  
Energy Parameter ◽  
Scalar Fields ◽  
Model Parameters ◽  
Interaction Term ◽  
Parameter Values ◽  
Chern Simons

AbstractThe present study reports reconstruction schemes for tachyon, k-essence and dilaton scalar field model of Dark Energy (DE) through Tsallis holographic dark fluid under the framework of Chern–Simons modified gravity. Reproducing the conservation equation for a coupled model with interaction term $Q=3H{b}^{2}{\rho }_{m}$ we have reconstructed the different scalar fields and the corresponding potentials. In the case of tachyon, ΛCDM fixed point is attained under this cosmological settings. Considering k-essence in this interacting situation, we have derived some constraints on the interaction term as well as Tsallis holographic dark energy parameter. Reconstructing dilaton scalar field, we have studied the behavior of scalar field and potential. In all those cases, the reconstructed Equation of State (EoS) parameters have been plotted and when computed for current universe z = 0 are found to be consistent with various observational data including Planck + WP + BAO. The only exception is a particular case of reconstructed k-essence model where phantom behavior is apparent, but its numerical value is deviated from the bounce set by the observations. Expressions for different constraints have been obtained and evolutionary behavior of reconstructed scalar fields and potentials for the various cases have been pictorially presented. Finally, we have developed a functional relationship between Hubble parameter and redshift and optimized the parameter values through χ2 minimization using the observed Hubble parameter values from Hai Yu et al. 2018 ApJ856 3.

Editorial [Dark Energy and Modified Gravity]

2010 ◽  
Vol 3 (2) ◽  
pp. 12-12
Author(s):  
S. Nojiri ◽  
S. D. Odintsov
Keyword(s):  
Dark Energy ◽  
Modified Gravity

Effective masses in a dense fermion background — Applied to neutrinos, dark matter and dark energy

2014 ◽  
Vol 29 (21) ◽  
pp. 1444010
Author(s):  
Bruce H. J. McKellar ◽  
T. J. Goldman ◽  
G. J. Stephenson
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Effective Mass ◽  
Negative Pressure ◽  
Expectation Value ◽  
Effective Masses ◽  
Neutrino Astrophysics

If fermions interact with a scalar field, and there are many fermions present the scalar field may develop an expectation value and generate an effective mass for the fermions. This can lead to the formation of fermion clusters, which could be relevant for neutrino astrophysics and for dark matter astrophysics. Because this system may exhibit negative pressure, it also leads to a model of dark energy.

scholarly journals SMOOTHED QUANTUM FLUCTUATIONS AND CMB OBSERVATIONS

2012 ◽  
Vol 21 (10) ◽  
pp. 1250080
Author(s):  
JAKUB MIELCZAREK ◽  
MICHAŁ KAMIONKA
Keyword(s):  
Scalar Field ◽  
Power Spectrum ◽  
Internal Structure ◽  
Planck Scale ◽  
Quantum Fluctuations ◽  
Gaussian Smoothing ◽  
Cosmic Inflation ◽  
Smoothing Factor ◽  
High Multipoles

In this paper, we investigate power spectrum of a smoothed scalar field. The smoothing leads to regularization of the UV divergences and can be related with the internal structure of the considered field or the space itself. We perform Gaussian smoothing to the quantum fluctuations generated during the phase of cosmic inflation. We study whether this effect can be probed observationally and conclude that the modifications of the power spectrum due to the smoothing on the Planck scale are negligible and far beyond the observational abilities. Subsequently, we investigate whether smoothing in any other form can be probed observationally. We introduce phenomenological smoothing factor e-k2σ2 to the inflationary spectrum and investigate its effects on the spectrum of CMB anisotropies and polarization. We show that smoothing can lead to suppression of high multipoles in the spectrum of the CMB. Based on seven years observations of WMAP satellite we indicate that the present scale of high multipoles suppression is constrained by σ < 3.19 Mpc (95% CL). This corresponds to the constraint σ < 100 μm at the end of inflation. Despite this value is far above the Planck scale, other processes of smoothing can be possibly studied with this constraint, as decoherence or diffusion of primordial perturbations.

scholarly journals RECONSTRUCTING A STRING-INSPIRED NONMINIMALLY COUPLED QUINTOM MODEL

2009 ◽  
Vol 18 (08) ◽  
pp. 1291-1301 ◽  
Author(s):  
M. R. SETARE ◽  
J. SADEGHI ◽  
A. R. AMANI
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
String Theory ◽  
Scalar Curvature ◽  
Recent Work ◽  
Nonminimal Coupling ◽  
Tachyon Field ◽  
Dynamical Dark Energy

Motivated by the recent work of Zhang and Chen,1we generalize their work to the nonminimally coupled case. We consider a quintom model of dark energy with a single scalar field T given by a Lagrangian inspired by a tachyonic Lagrangian in string theory. We consider nonminimal coupling of the tachyon field to the scalar curvature, and then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy.

scholarly journals Perturbed dark energy: Classical scalar field versus tachyon

2009 ◽  
Vol 80 (8) ◽  
Author(s):  
Olga Sergijenko ◽  
Bohdan Novosyadlyj
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Field Versus

BOUNDS ON f(G) GRAVITY FROM ENERGY CONDITIONS

2010 ◽  
Vol 25 (27) ◽  
pp. 2325-2332 ◽  
Author(s):  
PUXUN WU ◽  
HONGWEI YU
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Modified Gravity ◽  
Energy Conditions ◽  
Model Parameters ◽  
Effective Energy ◽  
Raychaudhuri Equation ◽  
Accelerating Expansion

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρm + ρE and p → pm + pE, where ρE and pE are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

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