scholarly journals PHANTOM FIELDS: BOUNCE SOLUTIONS IN THE EARLY UNIVERSE AND S-BRANES

2008 ◽  
Vol 17 (12) ◽  
pp. 2351-2358 ◽  
Author(s):  
VLADIMIR DZHUNUSHALIEV ◽  
VLADIMIR FOLOMEEV ◽  
KAIRAT MYRZAKULOV ◽  
RATBAY MYRZAKULOV
Keyword(s):  
Cosmological Model ◽  
Field Potential ◽  
Scalar Fields ◽  
Special Choice ◽  
De Sitter ◽  
Brane Solution ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Phantom Fields

A cosmological model with two phantom scalar fields with a special choice of the field potential is considered. The obtained regular solution describes a bounce with a subsequent transition to the de Sitter stage of the expansion of the universe. This solution could also be interpreted as an S-brane solution.

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.

scholarly journals Dark Sector in Cosmology: Dark Energy on Cosmological and Astrophysical Scales

2019 ◽  
Vol 64 (11) ◽  
pp. 998 ◽  
Author(s):  
B. Novosyadlyj
Keyword(s):  
Dark Energy ◽  
Scalar Fields ◽  
Dark Sector ◽  
Gravitational Fields ◽  
Current State ◽  
Astrophysical Objects ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Dynamical Dark Energy

The properties and observational manifestations of the dynamical dark energy on the cosmological and astrophysical scales are discussed. We consider the dynamical dark energy in the form of quintessential and phantom scalar fields with different parameters of the equation of state and the effective sound speed. The evolution of the dynamical dark energy and its impact on the dynamics of expansion of the Universe, halos, and voids, and its behavior in the static gravitational fields of astrophysical objects are analyzed. The current state and possible tests designed to establish the nature of dark energy are highlighted.

Cosmological spacetimes

2018 ◽  
Author(s):  
Nathalie Deruelle ◽  
Jean-Philippe Uzan
Keyword(s):  
Cosmological Model ◽  
Large Scale ◽  
Cosmic Time ◽  
De Sitter ◽  
Matter Distribution ◽  
Observable Universe ◽  
Cosmological Principle ◽  
Riemannian Spacetime ◽  
The Universe ◽  
Copernican Principle

This chapter provides a few examples of representations of the universe on a large scale—a first step in constructing a cosmological model. It first discusses the Copernican principle, which is an approximation/hypothesis about the matter distribution in the observable universe. The chapter then turns to the cosmological principle—a hypothesis about the geometry of the Riemannian spacetime representing the universe, which is assumed to be foliated by 3-spaces labeled by a cosmic time t which are homogeneous and isotropic, that is, ‘maximally symmetric’. After a discussion on maximally symmetric space, this chapter considers spacetimes with homogenous and isotropic sections. Finally, this chapter discusses Milne and de Sitter spacetimes.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

scholarly journals PRIMORDIAL BLACK HOLE FORMATION FROM INFLATON

2000 ◽  
Vol 09 (06) ◽  
pp. 705-710 ◽  
Author(s):  
XIN HE MENG ◽  
BIN WANG ◽  
S. FENG
Keyword(s):  
Black Hole ◽  
Primordial Black Hole ◽  
Primordial Black Holes ◽  
De Sitter ◽  
Hole Formation ◽  
Black Hole Formation ◽  
Expansion Of The Universe ◽  
Slow Rolling ◽  
The Relationship ◽  
The Universe

Measurements of the distances to SNe Ia have produced strong evidence that the expansion of the Universe is really accelarating, implying the existence of a nearly uniform component of dark energy with the simplest explanation as a cosmological constant. In this paper a small changing cosmological term is proposed, which is a function of a slow-rolling scalar field, by which the de Sitter primordial black holes' properties, for both charged and uncharged cases, are carefully examined and the relationship between the black hole formation and the energy transfer of the inflaton is eluciated. The criterion for primordial black hole formation is given.

scholarly journals BULK PHANTOM FIELDS, INCREASING WARP FACTORS AND FERMION LOCALIZATION

2005 ◽  
Vol 20 (05) ◽  
pp. 363-371 ◽  
Author(s):  
RATNA KOLEY ◽  
SAYAN KAR
Keyword(s):  
Mass Spectrum ◽  
Wave Functions ◽  
Warp Factor ◽  
Massless Spin ◽  
Brane Solution ◽  
Phantom Scalar ◽  
Phantom Scalar Field ◽  
Phantom Fields ◽  
Type Potential ◽  
Fermion Localization

A bulk phantom scalar field (with negative kinetic energy) in a sine–Gordon type potential is used to generate an exact thick brane solution with an increasing warp factor. It is shown that the growing nature of the warp factor allows the localization of massive as well as massless spin-1/2 fermions on the brane even without any additional non-gravitational interactions. The exact solutions for the localized massive fermionic modes are presented and discussed. The inclusion of a fermion–scalar Yukawa coupling appears to change the mass spectrum and wave functions of the localized fermion though it does not play the crucial role it did in the case of a decreasing warp factor.

scholarly journals Exploring the deviation of cosmological constant by a generalized pressure parameterization

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Jun-Chao Wang ◽  
Xin-He Meng
Keyword(s):  
Hubble Constant ◽  
Scalar Fields ◽  
Parametric Model ◽  
Matter Density ◽  
Density Parameter ◽  
Present Value ◽  
Big Rip ◽  
Phantom Scalar ◽  
Ultimate Fate ◽  
The Universe

Abstract We bring forward a generalized pressure (GP) parameterization for dark energy to explore the evolution of the universe. This parametric model has covered three common pressure parameterization types and can be reconstructed as quintessence and phantom scalar fields, respectively. We adopt the cosmic chronometer (CC) datasets to constrain the parameters. The results show that the inferred late-universe parameters of the GP parameterization are (within $$1\sigma $$1σ): the present value of Hubble constant $$H_{0}=(72.30^{+1.26}_{-1.37}) \ \hbox {km s}^{-1}\hbox { Mpc}^{-1}$$H0=(72.30-1.37+1.26)kms-1Mpc-1; the matter density parameter $$\Omega _{\text {m0}}=0.302^{+0.046}_{-0.047}$$Ωm0=0.302-0.047+0.046, and the bias of the universe towards quintessence. Then we perform a dynamic analysis on the GP parameterization and find that there is an attractor or a saddle point in the system corresponding to the different values of the parameters. Finally, we discuss the ultimate fate of the universe under the phantom scenario in the GP parameterization. It is demonstrated that the three cases of pseudo rip, little rip, and big rip are all possible.

Bulk viscosity in Friedmann universe with a varying speed of light described by modified equation of state

2015 ◽  
Vol 12 (10) ◽  
pp. 1550126
Author(s):  
G. S. Khadekar ◽  
Arti Ghogre
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Scale Factor ◽  
Special Choice ◽  
Speed Of Light ◽  
Dependent Parameter ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Modified Equation ◽  
Universe Evolution

We solve the Freidmann equations by considering a universe media as a bulk viscosity described by a modified equation of state (EOS) of the form p = (γ - 1)ρc2 + Λ(t). A completely integrable dynamical equation to the scale factor is obtained and gives out the exact solution by assuming that the time-dependent parameter Λ and the bulk viscosity are linear combination of two and three terms, respectively and is expressed as: [Formula: see text] and [Formula: see text], where R is a scale factor and Λ0, Λ1, ζ0, ζ1, ζ2, are constants. For a special choice of the parameters, we discuss the acceleration expansion of the universe evolution and future singularities in the framework of variable speed of light (VSL) theory.

scholarly journals A novel teleparallel dark energy model

2016 ◽  
Vol 25 (02) ◽  
pp. 1650025 ◽  
Author(s):  
Giovanni Otalora
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Teleparallel Gravity ◽  
Accelerated Expansion ◽  
Late Time ◽  
De Sitter ◽  
Sitter Group ◽  
Current State ◽  
Expansion Of The Universe ◽  
The Universe

Although equivalent to general relativity, teleparallel gravity (TG) is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the “vector torsion”. This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group [Formula: see text]. It is found that the current state of accelerated expansion of the universe corresponds to a late-time attractor that can be (i) a dark energy-dominated de Sitter solution ([Formula: see text]), (ii) a quintessence-type solution with [Formula: see text], or (iii) a phantom-type [Formula: see text] dark energy.

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