scholarly journals SPECTRA OF RELIC GRAVITONS AND BRANS–DICKE THEORY

2005 ◽  
Vol 20 (02) ◽  
pp. 127-134 ◽  
Author(s):  
B. K. SAHOO
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Time Dependence ◽  
Gravitational Waves ◽  
Hubble Parameter ◽  
Frequency Dependent ◽  
Cosmological Expansion ◽  
Relic Gravitational Waves ◽  
Matter Energy ◽  
Inflationary Models

The spectra of relic gravitational waves produced as a result of cosmological expansion of the inflationary models are derived in Brans–Dicke (BD) theory of gravity. The time dependence of the very early Hubble parameter and matter energy density are derived from frequency-dependent spectrum of relic gravitational waves. Also it is found that Brans–Dicke scalar field contributes to the energy density of relic gravitons.

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.

scholarly journals ON THEORY OF REGULAR ACCELERATING UNIVERSE IN RIEMANN–CARTAN SPACETIME

2013 ◽  
Vol 28 (21) ◽  
pp. 1350090 ◽  
Author(s):  
A. V. MINKEVICH
Keyword(s):  
Energy Density ◽  
Hubble Parameter ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Accelerating Universe ◽  
Cosmological Expansion ◽  
Isotropic Cosmology ◽  
In The Beginning ◽  
Curvature Tensors

Isotropic cosmology built in the Riemann–Cartan spacetime is investigated. Properties of homogeneous isotropic cosmological models filled with usual gravitating matter and scalar fields are studied in the beginning of cosmological expansion near the limiting energy density. It is shown that cosmological models are regular not only with respect to the Hubble parameter and the energy density but also with respect to the torsion and curvature tensors.

scholarly journals Relic gravitational waves in cosmological models based on the modified gravity theories

2021 ◽  
Vol 2081 (1) ◽  
pp. 012002
Author(s):  
I V Fomin ◽  
S V Chervon
Keyword(s):  
Energy Density ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Direct Detection ◽  
Cosmological Models ◽  
Observational Constraints ◽  
Cosmological Perturbations ◽  
Modified Gravity Theories ◽  
Relic Gravitational Waves ◽  
Gravity Theories

Abstract We consider cosmological models based on the generalized scalar-tensor gravity, which correspond to the observational constraints on the parameters of cosmological perturbations for any model’s parameters. The estimates of the energy density of relic gravitational waves for such a cosmological models were made. The possibility of direct detection of such a gravitational waves using modern and prospective methods was discussed as well.

Cosmology via thermodynamics of polytropic gas

2017 ◽  
Vol 32 (32) ◽  
pp. 1750177 ◽  
Author(s):  
Muzaffer Askin ◽  
Mustafa Salti ◽  
Oktay Aydogdu
Keyword(s):  
Dark Matter ◽  
Scalar Field ◽  
Energy Density ◽  
Exact Expression ◽  
Frw Universe ◽  
Polytropic Gas ◽  
Friedmann Robertson Walker ◽  
Matter Energy

We study cosmological scenarios of the polytropic gas (PG) dark matter-energy proposal in a Friedmann–Robertson–Walker (FRW) Universe. As a first step, we obtain an exact expression for the energy density of PG model by making use of the thermodynamics. Later, we investigate some cosmological quantities and perform neo-classical analyzes. Finally, we implement a connection between the PG and a homogenous minimally coupled scalar field by introducing its self-interacting potential.

SUPERQUINTESSENCE

2002 ◽  
Vol 11 (04) ◽  
pp. 471-481 ◽  
Author(s):  
VALERIO FARAONI
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Gravitational Wave ◽  
Gravitational Waves ◽  
Ricci Curvature ◽  
Wave Spectra ◽  
Scalar Field Models ◽  
Acceleration Of The Universe ◽  
The Universe

There is marginal evidence that the quintessential form of matter responsible for the acceleration of the universe observed today has ratio between pressure and energy density w < -1. Such a regime, called superacceleration, cannot be achieved with conventional scalar field models. The simplest nonexotic model achieving superacceleration is that of a scalar field nonminimally coupled to the Ricci curvature. This model is studied for general potentials and an exact superaccelerating solution is presented. In quintessential inflation, the model can have blue gravitational wave spectra, improving the prospects for the detection of cosmological gravitational waves.

scholarly journals Gravitational waves generation in turbulent hypermagnetic fields before the electroweak phase transition

2022 ◽  
Vol 2022 (01) ◽  
pp. 021
Author(s):  
Maxim Dvornikov
Keyword(s):  
Phase Transition ◽  
Energy Density ◽  
Gravitational Waves ◽  
Magnetic Effect ◽  
Higgs Bosons ◽  
Magnetic Hydrodynamics ◽  
Electroweak Phase Transition ◽  
Chiral Magnetic Effect ◽  
Relic Gravitational Waves ◽  
Symmetric Phase

Abstract We study the production of relic gravitational waves (GWs) in turbulent hypermagnetic fields (HMFs) in the symmetric phase of the early universe before the electroweak phase transition (EWPT). The noise of HMFs is modeled by the analog of the magnetic hydrodynamics turbulence. The evolution of HMFs is driven by the analogs of the chiral magnetic effect and the Adler anomalies in the presence of the nonzero asymmetries of leptons and Higgs bosons. We track the evolution of the energy density of GWs from 10 TeV down to EWPT and analyze its dependence on the parameters of the system. We also discuss the possibility to observe the predicted GW background by the current GW detectors.

scholarly journals Dynamical system analysis of FLRW models with Modified Chaplygin gas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ali Osman Yılmaz ◽  
Ertan Güdekli
Keyword(s):  
Dynamical System ◽  
Equation Of State ◽  
Energy Density ◽  
System Analysis ◽  
Chaplygin Gas ◽  
Modified Chaplygin Gas ◽  
State Spaces ◽  
The Universe ◽  
Matter Energy ◽  
Far Future

AbstractWe investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and cosmological constant, using dynamical system methods. We assume $$p=(\gamma -1)\mu -\dfrac{A}{\mu ^\alpha }$$ p = ( γ - 1 ) μ - A μ α as equation of state where $$\mu$$ μ is the matter-energy density, p is the pressure, $$\alpha$$ α is a parameter which can take on values $$0<\alpha \le 1$$ 0 < α ≤ 1 as well as A and $$\gamma$$ γ are positive constants. We draw the state spaces and analyze the nature of the singularity at the beginning, as well as the fate of the universe in the far future. In particular, we address the question whether there is a solution which is stable for all the cases.

scholarly journals Imprint of gravitational waves in models dominated by a dynamical cosmic scalar field

1998 ◽  
Vol 57 (10) ◽  
pp. 6057-6064 ◽  
Author(s):  
R. R. Caldwell ◽  
Paul J. Steinhardt
Keyword(s):  
Scalar Field ◽  
Gravitational Waves
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