scholarly journals Cosmological Solutions from a Multi-Measure Model with Inflaton Field

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1387 ◽  
Author(s):  
Denitsa Staicova ◽  
Michail Stoilov
Keyword(s):  
Riemannian Metric ◽  
Small Time ◽  
Model Parameters ◽  
Riemannian Volume ◽  
Accelerating Expansion ◽  
Type Ia ◽  
Measure Model ◽  
Complicated Model ◽  
Supernovae Type Ia ◽  
The Universe

In a recent work, we demonstrated that a modified gravity model in which a scalar “darkon” field is coupled to both the standard Riemannian metric and to another non-Riemannian volume form is compatible with observational data from Supernovae Type Ia. Here, we investigate a more complicated model with an additional “inflaton” scalar field. We demonstrate numerically that the model can qualitatively reproduce the Universe inflation epoch, matter dominated epoch, and present accelerating expansion in a seamless way. We show that such solutions occur only when the model parameters are within a very particular range. The main numerical problem we are faced with is reproducing the extremely small time of the inflation epoch. Here, we present how the variation of some parameters affects this time.

A new pressure-parametric cosmological model

2020 ◽  
Vol 35 (25) ◽  
pp. 2050209
Author(s):  
Yan-Hong Yao ◽  
Xin-He Meng
Keyword(s):  
Scalar Fields ◽  
Model Parameters ◽  
Acoustic Oscillations ◽  
Dark Sector ◽  
Type Ia ◽  
Phantom Scalar ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

We put forward a pressure-parametric model to study the tiny deviation from cosmological constant(CC) behavior of the dark sector accelerating the expansion of the Universe. Data from cosmic microwave background (CMB) anisotropies, baryonic acoustic oscillations (BAO), Type Ia supernovae (SN Ia) observation are applied to constrict the model parameters. The constraint results show that such model suffers with [Formula: see text] tension as well. To realize this model more physically, we reconstruct it with the quintessence and phantom scalar fields, and find out that although the model predicts a quintessence-induced acceleration of the Universe at past and present, at some moment of the future, dark energy’s density have a disposition to increase.

Transit dark energy string cosmological models with perfect fluid in F(R,T)-gravity

2018 ◽  
Vol 15 (10) ◽  
pp. 1850168 ◽  
Author(s):  
Rashid Zia ◽  
Dinesh Chandra Maurya ◽  
Anirudh Pradhan
Keyword(s):  
Dark Energy ◽  
Early Time ◽  
Momentum Tensor ◽  
Late Time ◽  
Field Equations ◽  
Accelerating Expansion ◽  
Type Ia ◽  
Dynamical Parameters ◽  
The Stability ◽  
The Universe

In this paper, spatially homogeneous and anisotropic Bianchi type-[Formula: see text] dark energy (DE) cosmological transit models with string fluid source in [Formula: see text] gravity [T. Harko et al., Phys. Rev. D 84 (2011) 024020], where [Formula: see text] is the Ricci scalar and [Formula: see text] the trace of the stress energy–momentum tensor, have been studied in the context of early time decelerating and late-time accelerating expansion of the Universe as suggested by the recent observations. The exact solutions of the field equations are obtained first by using generalized hybrid expansion law (HEL) [Formula: see text] which yields a time-dependent deceleration parameter [Formula: see text] and second by considering the metric coefficient [Formula: see text]. By using recent constraints from supernovae type-Ia union data [Cunha, arXiv:0811.2379[astro-ph]], we obtain [Formula: see text] and [Formula: see text] for transit model [Formula: see text]. The Universe has an initial singularity and is anisotropic closed and it tends to be flat at the late time, i.e. our Universe is in accelerating expansion. Our model shows a phase transition property from decelerating to accelerating. It is remarkable to mention here that our Universe is homogeneous and anisotropic in the early phase whereas it becomes homogeneous and isotropic for [Formula: see text]. We have also discussed the stability of the background solution with respect to perturbations of the metric along with the properties of future singularities in the Universe dominated by DE including the phantom-type fluid. Various physical and dynamical parameters are also calculated and investigated in terms of time and redshift both.

scholarly journals Cosmological aspects of a unified dark energy and dust dark matter model

2016 ◽  
Vol 32 (01) ◽  
pp. 1750006 ◽  
Author(s):  
Denitsa Staicova ◽  
Michail Stoilov
Keyword(s):  
Phase Transition ◽  
Dark Matter ◽  
Dark Energy ◽  
Maximal Rank ◽  
Volume Form ◽  
Riemannian Volume ◽  
Type Ia ◽  
Lower Energy Density ◽  
Supernovae Type Ia ◽  
Universe Evolution

Recently, a model of modified gravity plus single scalar field was proposed, in which the scalar couples both to the standard Riemannian volume form given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume form given in terms of an auxiliary maximal rank antisymmetric tensor gauge field. This model provides an exact unified description of both dark energy (via dynamically generated cosmological constant) and dark matter (as a “dust” fluid due to a hidden nonlinear Noether symmetry). In this paper, we test the model against Supernovae type Ia experimental data and investigate the future Universe evolution which follows from it. Our results show that this model has very interesting features allowing various scenarios of Universe evolution and in the same time perfectly fits contemporary observational data. It can describe exponentially expanding or finite expanding Universe and moreover, a Universe with phase transition of first kind. The phase transition occurs to a new, emerging at some time ground state with lower energy density, which affects significantly the Universe evolution.

scholarly journals Constraints and cosmography of $$\Lambda $$CDM in presence of viscosity

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
L. Herrera-Zamorano ◽  
A. Hernández-Almada ◽  
Miguel A. García-Aspeitia
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Physical Mechanism ◽  
Viscosity Coefficient ◽  
Model Parameters ◽  
Two Samples ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe ◽  
Good Agreement

Abstract In this work, we study two scenarios of the Universe filled by a perfect fluid following the traditional dark energy and a viscous fluid as dark matter. In this sense, we explore the most simple case for the viscosity in the Eckart formalism, a constant, and then, a polynomial function of the redshift. We constrain the phase-space of the model parameters by performing a Bayesian analysis based on Markov Chain Monte Carlo method and using the latest data of the Hubble parameter (OHD), Type Ia Supernovae (SNIa) and Strong Lensing Systems. The first two samples cover the region $$0.01<z<2.36$$0.01<z<2.36. Based on AIC, we find equally support of these viscous models over Lambda-Cold Dark Matter (LCDM) taking into account OHD or SNIa. On the other hand, we reconstruct the cosmographic parameters (q, j, s, l) and find good agreement to LCDM within up to $$3\sigma $$3σ CL. Additionally, we find that the cosmographic parameters and the acceleration-deceleration transition are sensible to the parameters related to the viscosity coefficient, making of the viscosity an interesting physical mechanism to modified them.

scholarly journals Supernovae Type Ia: non-standard candles of the Universe

2011 ◽  
Author(s):  
Alexey Bogomazov ◽  
A. V. Tutukov
Keyword(s):  
Type Ia ◽  
Supernovae Type Ia ◽  
The Universe

scholarly journals Universe opacity and Type Ia supernova dimming

2019 ◽  
Vol 489 (1) ◽  
pp. L63-L68 ◽  
Author(s):  
Václav Vavryčuk
Keyword(s):  
Cold Dark Matter ◽  
Hubble Constant ◽  
Light Extinction ◽  
Universe Model ◽  
Type Ia Supernova ◽  
Accelerating Expansion ◽  
Λcdm Model ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

ABSTRACT In this paper, I revoke a debate about an origin of Type Ia supernova (SN Ia) dimming. I argue that except for a commonly accepted accelerating expansion of the Universe, a conceivable alternative for explaining this observation is universe opacity caused by light extinction by intergalactic dust, even though it is commonly assumed that this effect is negligible. Using data of the Union2.1 SN Ia compilation, I find that the standard Λ cold dark matter (ΛCDM) model and the opaque universe model fit the SN Ia measurements at redshifts z < 1.4 comparably well. The optimum solution for the opaque universe model is characterized by the B-band intergalactic opacity $\lambda _{B} = 0.10 \pm 0.03 \, \mathrm{Gpc}^{-1}$ and the Hubble constant $H_0 = 68.0 \pm 2.5 \, \mathrm{km\, s^{-1}\, Mpc^{-1}}$. The intergalactic opacity is higher than that obtained from independent observations but still within acceptable limits. This result emphasizes that the issue of the accelerating expansion of the Universe as the origin of the SN Ia dimming is not yet definitely resolved. Obviously, the opaque universe model as an alternative to the ΛCDM model is attractive, because it avoids puzzles and controversies associated with dark energy and the accelerating expansion.

scholarly journals EXPLAINING THE SUPERNOVA DATA WITHOUT ACCELERATING EXPANSION

2012 ◽  
Vol 21 (11) ◽  
pp. 1242021 ◽  
Author(s):  
W. M. STUCKEY ◽  
T. J. McDEVITT ◽  
M. SILBERSTEIN
Keyword(s):  
General Relativity ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Nobel Prize ◽  
De Sitter ◽  
Accelerating Expansion ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Nobel Prize In Physics ◽  
The Universe

The 2011 Nobel Prize in Physics was awarded "for the discovery of the accelerating expansion of the universe through observations of distant supernovae." However, it is not the case that the type Ia supernova data necessitates accelerating expansion. Since we do not have a successful theory of quantum gravity, we should not assume general relativity (GR) will survive unification intact, especially on cosmological scales where tests are scarce. We provide a simple example of how GR cosmology may be modified to produce a decelerating Einstein-de Sitter cosmology (EdS) that accounts for the Union2 Compilation data as well as the accelerating ΛCDM (EdS plus a cosmological constant).

scholarly journals Testing dissipative dark matter in causal thermodynamics

2020 ◽  
pp. 2150032
Author(s):  
Norman Cruz ◽  
Esteban González ◽  
Guillermo Palma
Keyword(s):  
Dark Matter ◽  
Accelerated Expansion ◽  
Model Parameters ◽  
Fitted Parameter ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Viscous Pressure ◽  
Ia Supernovae ◽  
Parameter Values ◽  
The Universe

In this paper we study the consistency of a cosmological model representing a universe filled with a one-component dissipative dark matter fluid, in the framework of the causal Israel–Stewart theory, where a general expression arising from perturbation analysis for the relaxation time [Formula: see text] is used. This model is described by an exact analytic solution recently found in [N. Cruz, E. González and G. Palma, Gen. Relat. Gravit. 52, 62 (2020), which depends on several model parameters as well as integration constants, allowing the use of Type Ia Supernovae and Observational Hubble data to perform by an astringent observational tests. The constraint regions found for the parameters of the solution allow the existence of an accelerated expansion of the universe at late times, after the domination era of the viscous pressure, which holds without the need of including a cosmological constant. Nevertheless, the fitted parameter values lead to drawbacks as a very large non-adiabatic contribution to the speed of sound, and some inconsistencies, not totally conclusive, with the description of the dissipative dark matter as a fluid, which is nevertheless a common feature of these kind of models.

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.

Sign in / Sign up

Export Citation Format

Share Document