Cosmological dynamics of a nonminimally coupled scalar field system and its late time cosmic relevance

AbstractScalar field cosmologies with a generalized harmonic potential and a matter fluid with a barotropic equation of state (EoS) with barotropic index $$\gamma $$ γ for the locally rotationally symmetric (LRS) Bianchi I and flat Friedmann–Lemaître–Robertson–Walker (FLRW) metrics are investigated. Methods from the theory of averaging of nonlinear dynamical systems are used to prove that time-dependent systems and their corresponding time-averaged versions have the same late-time dynamics. Therefore, the simplest time-averaged system determines the future asymptotic behavior. Depending on the values of $$\gamma $$ γ , the late-time attractors of physical interests are flat quintessence dominated FLRW universe and Einstein-de Sitter solution. With this approach, the oscillations entering the system through the Klein–Gordon (KG) equation can be controlled and smoothed out as the Hubble parameter H – acting as time-dependent perturbation parameter – tends monotonically to zero. Numerical simulations are presented as evidence of such behavior.

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Modern Topics in Scalar Field Cosmology

10.23889/suthesis.56561 ◽

2020 ◽

Author(s):

◽

Cari Powell

Keyword(s):

Dark Matter ◽

Scalar Field ◽

Gravitational Wave ◽

Gravitational Waves ◽

Mass Range ◽

Distant Future ◽

Field System ◽

Stochastic Background ◽

Scalar Field Cosmology

The aim of this research is to use modern techniques in scalar ﬁeld Cosmol-ogy to produce methods of detecting gravitational waves and apply them to current gravitational waves experiments and those that will be producing results in the not too distant future. In the ﬁrst chapter we discuss dark matter and some of its candidates, speciﬁcally, the axion. We then address its relationship with gravitational waves. We also discuss inﬂation and how it can be used to detect gravitational waves. Chapter 2 concentrates on constructing a multi ﬁeld system of axions in order to increase the mass range of the ultralight axion, putting it into the observation range of pul-sar timing arrays. Chapter 3 discusses non-attractor inﬂation which is able to enhance stochastic background gravitational waves at scales that allows them to be measured by gravitational wave experiments. Chapter 4 uses a similar method to chapter 3 and applies it to 3-point overlap functions for tensor, scalar and a combination of the two polarisations.

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Bouncing scenario in Brans–Dicke theory

International Journal of Geometric Methods in Modern Physics ◽

10.1142/s0219887820500565 ◽

2020 ◽

Vol 17 (04) ◽

pp. 2050056

Author(s):

Sunil Kumar Tripathy ◽

Subingya Pandey ◽

Alaka Priyadarsini Sendha ◽

Dipanjali Behera

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Equation Of State ◽

Linear Equation ◽

Scale Factor ◽

Cosmic Acceleration ◽

Late Time ◽

Dark Fluid

A bouncing scenario is studied in the framework of generalized Brans–Dicke theory. In order to have a dark energy (DE) driven late time cosmic acceleration, we have considered a unified dark fluid simulated by a linear equation of state (EoS). The evolutionary behavior of the DE equation of parameter derived from the unified dark fluid has been discussed. The effect of the bouncing scale factor on the Brans–Dicke parameter, self-interacting potential and the Brans–Dicke scalar field is investigated.

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Cosmic acceleration with tachyon field

Modern Physics Letters A ◽

10.1142/s0217732318501997 ◽

2018 ◽

Vol 33 (34) ◽

pp. 1850199 ◽

Cited By ~ 1

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.

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Conformal scattering of the Maxwell-scalar field system on de Sitter space

Journal of Hyperbolic Differential Equations ◽

10.1142/s021989161950019x ◽

2019 ◽

Vol 16 (04) ◽

pp. 743-791

Author(s):

Grigalius Taujanskas

Keyword(s):

Scalar Field ◽

De Sitter Space ◽

Decay Rates ◽

Energy Estimates ◽

Small Data ◽

De Sitter ◽

Null Infinity ◽

Conformally Invariant ◽

Field System ◽

Gauge Fixing

We prove small data energy estimates of all orders of differentiability between past null infinity and future null infinity of de Sitter space for the conformally invariant Maxwell-scalar field system. Using these, we construct bounded and invertible, but nonlinear, scattering operators taking past asymptotic data to future asymptotic data. We deduce exponential decay rates for solutions with data having at least two derivatives, and for more regular solutions discover an asymptotic decoupling of the scalar field from the charge. The construction involves a carefully chosen complete gauge fixing condition which allows us to control all components of the Maxwell potential, and a nonlinear Grönwall inequality for higher-order estimates.

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Quintessence in low-energy effective theory

EPJ Web of Conferences ◽

10.1051/epjconf/201816808004 ◽

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.

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GLOBAL EXISTENCE TO THE EINSTEIN-SCALAR FIELD SYSTEM ON THE ROBERTSON–WALKER SPACE-TIMES WITH HYPERBOLIC AND SPHERICAL SYMMETRIES

Journal of Hyperbolic Differential Equations ◽

10.1142/s0219891610002074 ◽

2010 ◽

Vol 07 (01) ◽

pp. 69-83

Author(s):

NORBERT NOUTCHEGUEME ◽

ALEXIS NANGUE

Keyword(s):

Asymptotic Behavior ◽

Scalar Field ◽

Global Existence ◽

Initial Velocity ◽

Existence Of Solutions ◽

Expansion Factor ◽

Positive Cosmological Constant ◽

Field System ◽

Global Existence Of Solutions ◽

Cosmological Expansion

Global existence of solutions is proved and asymptotic behavior is investigated, in the case of a positive cosmological constant and positive initial velocity of the cosmological expansion factor.

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Chameleon field dynamics during inflation

International Journal of Modern Physics D ◽

10.1142/s0218271818500414 ◽

2018 ◽

Vol 27 (04) ◽

pp. 1850041 ◽

Cited By ~ 2

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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