scholarly journals Dynamics of two-scalar-field cosmological models beyond the exponential potential

2017 ◽  
Vol 26 (14) ◽  
pp. 1750164 ◽  
Author(s):  
Yu Li
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Cosmological Models ◽  
The Other ◽  
Late Time ◽  
Exponential Potential ◽  
Multiple Attractors ◽  
Evolution Of The Universe ◽  
The Universe

In this paper, we discuss the dynamics of two- scalar-field cosmological models. Unlike in the situation of exponential potential, we find that there are late-time attractors in which one scalar field dominates the energy density of universe and the other one decay. We also discuss the possibility of multiple attractors model which is useful to realize the evolution of the universe from a scaling era to recent acceleration era. We also give the conditions of the existence of multiple attractors.

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.

Late time cosmology in f(R,G)- gravity with interacting fluids

2022 ◽  
Author(s):  
Bikash Chandra Paul ◽  
A. Chanda ◽  
Sunil Maharaj ◽  
Aroonkumar Beesham
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Cosmological Parameters ◽  
Accelerating Universe ◽  
Model Parameters ◽  
Density Parameter ◽  
Late Time ◽  
First Case ◽  
The Universe

Abstract Cosmological models are obtained in a $f(R)$ modified gravity with a coupled Gauss-Bonnet (GB) terms in the gravitational action. The dynamical role of the GB terms is explored with a coupled dilaton field in two different cases (I) $f(R)= R + \gamma R^2- \lambda \left( \frac{R}{3m_s^2} \right)^{\delta}$ where $\gamma$, $\lambda$ and $\delta$ are arbitrary constants and (II) $f(R)=R$ and estimate the constraints on the model parameters. In the first case we choose GB terms coupled with a free scalar field in the presence of interacting fluid and in the second case GB terms coupled with scalar field in a self interacting potential to compare the observed universe. The evolutionary scenario of the universe is obtained adopting a numerical technique as the field equations are highly non-linear. Defining a new density parameter $\Omega_{H}$, a ratio of the dark energy density to the present energy density of the non-relativistic matter, we look for a late accelerating universe. The state finder parameters $\Omega_{H}$, deceleration parameter ($q$), jerk parameter ($j$) are plotted. It is noted that a non-singular universe with oscillating cosmological parameters for a given strength of interactions is admitted in Model-I. The gravitational coupling constant $\lambda$ is playing an important role. The Lagrangian density of $f(R)$ is found to dominate over the GB terms when oscillating phase of dark energy arises. In Model-II, we do not find oscillation of the cosmological parameters as the universe evolves. In the presence of interaction the energy from radiation sector of matter cannot flow to the other two sectors of fluid. The range of values of the strengths of interaction of the fluids are estimated for a stable universe assuming the primordial gravitational wave speed equal to unity.

scholarly journals A LATE TIME ACCELERATION OF THE UNIVERSE WITH TWO SCALAR FIELDS: MANY POSSIBILITIES

2006 ◽  
Vol 21 (35) ◽  
pp. 2663-2670 ◽  
Author(s):  
NARAYAN BANERJEE ◽  
SUDIPTA DAS
Keyword(s):  
Scalar Field ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
The Other ◽  
Field Conditions ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

In the present work, an attempt has been made to explain the recent cosmic acceleration of the universe with two mutually interacting scalar fields, one being the Brans–Dicke scalar field and the other a quintessence scalar field. Conditions have been derived for which the quintessence scalar field has an early oscillation and it grows during a later time to govern the dynamics of the universe.

INFLATION IN BIANCHI MODELS AND COSMIC NO-HAIR THEOREM IN EINSTEIN–CARTAN THEORY

2003 ◽  
Vol 12 (05) ◽  
pp. 833-842
Author(s):  
SUBENORY CHAKROBORTY ◽  
SULAGNA CHAKRABARTI
Keyword(s):  
Scalar Field ◽  
Late Time ◽  
Time Behaviour ◽  
Bianchi Models ◽  
Evolution Of The Universe ◽  
Cartan Theory ◽  
The Universe

We have examined cosmic no-hair theorem for anisotropic Bianchi-models in Einstein–Cartan theory and it is possible to have inflationary solution with a scalar field. It has been noted that during the inflationary era, the evolution of the Universe does not depend on the form of the potential but the late time behaviour is dependent on the potential for the inflation field.

BLACK HOLE - DESTROYER

2021 ◽  
Author(s):  
Иштимер Шагалиевич Хурамшин
Keyword(s):  
Black Hole ◽  
The Other ◽  
Baryonic Matter ◽  
Evolution Of The Universe ◽  
The Galaxy ◽  
The One ◽  
The Universe

В статье обсуждается вопрос о двух противоположных функциях черной дыры. С одной стороны она является творцом для галактики, а с другой - разрушителем барионной материи. Предполагается, что эти функции заложены самой эволюцией Вселенной. Деструкция материи до фотонов в ЧД считается наиболее вероятным событием. The question of two opposite functions of a black hole is discussed. On the one hand, it is the creator for the galaxy, and on the other-the destroyer of baryonic matter. It is assumed that these functions were laid down by the evolution of the Universe itself. The destruction of matter to photons in BH is considered the most likely event.

scholarly journals The investigation of detectability of the relic gravitational waves based on the WMAP-9 and Planck

2017 ◽  
Vol 26 (02) ◽  
pp. 1750003 ◽  
Author(s):  
Basem Ghayour
Keyword(s):  
Scalar Field ◽  
Gravitational Waves ◽  
Crucial Role ◽  
Planck Data ◽  
Evolution Of The Universe ◽  
Cosmological Observations ◽  
Relic Gravitational Waves ◽  
The Waves ◽  
The Universe ◽  
General Range

The generated relic gravitational waves underwent several stages of evolution of the universe such as inflation and reheating. These stages were affected on the shape of spectrum of the waves. As well known, at the end of inflation, the scalar field [Formula: see text] oscillates quickly around some point where potential [Formula: see text] has a minimum. The end of inflation stage played a crucial role on the further evolution stages of the universe because particles were created and collisions of the created particles were responsible for reheating the universe. There is a general range for the frequency of the spectrum [Formula: see text])[Formula: see text]Hz. It is shown that the reheating temperature can affect on the frequency of the spectrum as well. There is constraint on the temperature from cosmological observations based on WMAP-9 and Planck. Therefore, it is interesting to estimate allowed value of frequencies of the spectrum based on general range of reheating temperature like few MeV [Formula: see text] GeV, WMAP-9 and Planck data then compare the spectrum with sensitivity of future detectors such as LISA, BBO and ultimate-DECIGIO. The obtained results of this comparison give us some more chance for detection of the relic gravitational waves.

Cosmic acceleration with tachyon field

2018 ◽  
Vol 33 (34) ◽  
pp. 1850199 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Tachyon Field ◽  
Minimal Coupling ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

scholarly journals Quintessence in low-energy effective theory

2018 ◽  
Vol 168 ◽  
pp. 08004
Author(s):  
Tae Hoon Lee
Keyword(s):  
Scalar Field ◽  
Effective Potential ◽  
Cosmological Solution ◽  
Low Energy ◽  
Effective Theory ◽  
Late Time ◽  
Inverse Power Law ◽  
Virtual Interactions ◽  
The Universe ◽  
Gravitational Equations

Considering a theory of Brans-Dicke gravity with general couplings of a heavy field, we derive the low-energy effective theory action in the universe of temperature much lower than the heavy field mass. Gravitational equations and the Brans-Dicke scalar field equation including an effective potential of the scalar field are obtained, which is induced through virtual interactions of the heavy field in the late-time universe. We find a deSitter cosmological solution stemming from the inverse power law effective potential of the scalar field and discuss the possibility that the late time acceleration of our universe can be described by means of the solution.

scholarly journals Chameleon field dynamics during inflation

2018 ◽  
Vol 27 (04) ◽  
pp. 1850041 ◽  
Author(s):  
Nasim Saba ◽  
Mehrdad Farhoudi
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Big Bang ◽  
Late Time ◽  
Inflationary Model ◽  
Slow Roll ◽  
Equation Of State Parameter ◽  
The Common ◽  
The Universe

By studying the chameleon model during inflation, we investigate whether it can be a successful inflationary model, wherein we employ the common typical potential usually used in the literature. Thus, in the context of the slow-roll approximations, we obtain the e-folding number for the model to verify the ability of resolving the problems of standard big bang cosmology. Meanwhile, we apply the constraints on the form of the chosen potential and also on the equation of state parameter coupled to the scalar field. However, the results of the present analysis show that there is not much chance of having the chameleonic inflation. Hence, we suggest that if through some mechanism the chameleon model can be reduced to the standard inflationary model, then it may cover the whole era of the universe from the inflation up to the late time.

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