scholarly journals Gauss–Bonnet term corrections in scalar field cosmology

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Igor Fomin
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Einstein Gravity ◽  
Minimal Coupling ◽  
Evolution Of The Universe ◽  
Scalar Field Cosmology ◽  
The Universe ◽  
Bonnet Term ◽  
Inflationary Models

AbstractThe influence of non-minimal coupling of a scalar field and the Gauss–Bonnet term on the inflationary stage of evolution of the universe is investigated in this paper. The main cosmological effects of such a coupling were considered. The deviations between Einstein–Gauss–Bonnet inflation and standard one based on Einstein gravity were determined. The corrections of a weak GB coupling preserving the type of the scalar field potential to standard inflationary models is considered as well.

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 Nutty black holes in Galileon scalar-tensor gravity

2018 ◽  
Vol 33 (32) ◽  
pp. 1850189 ◽  
Author(s):  
A. Brandelet ◽  
Y. Brihaye ◽  
T. Delsate ◽  
L. Ducobu
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Einstein Gravity ◽  
Parameter Family ◽  
Hairy Black Holes ◽  
Two Parameter ◽  
Bonnet Term

Einstein gravity supplemented by a scalar field nonminimally coupled to a Gauss–Bonnet term provides an example of model of scalar-tensor gravity where hairy black holes do exist. We consider the classical equations within a metric endowed with a NUT-charge and obtain a two-parameter family of nutty-hairy black holes. The pattern of these solutions in the exterior and the interior of their horizon is studied in some details. The influence of both — the hairs and the NUT-charge — on the lightlike and timelike geodesics is emphasized.

A study of dynamical equations for non-minimally coupled scalar field using Noether symmetric approach

2016 ◽  
Vol 31 (19) ◽  
pp. 1650116 ◽  
Author(s):  
Sourav Dutta ◽  
Madan Mohan Panja ◽  
Subenoy Chakraborty
Keyword(s):  
Scalar Field ◽  
Infinitesimal Generator ◽  
Einstein Gravity ◽  
Matter Content ◽  
The Self ◽  
Noether Symmetry ◽  
Dynamical Equations ◽  
Augmented Space ◽  
Constants Of Motion ◽  
Scalar Field Cosmology

Non-minimally coupled scalar field cosmology has been studied in this work within the framework of Einstein gravity. In the background of homogeneous and isotropic Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime non-minimally coupled scalar field having self-interacting potential is taken as the source of the matter content. The constraint of imposing Noether symmetry on the Lagrangian of the system not only determines the infinitesimal generator (the symmetry vector) but also the coupling function and the self-interacting potential for the scalar field. By choosing appropriately a point transformation in the augmented space, one of the transformed variables is cyclic for the Lagrangian. Finally, using constants of motion, the solutions are analyzed.

Scalar field potential in inflationary models: Reconstruction and further constraints

1995 ◽  
Vol 51 (12) ◽  
pp. 6722-6735 ◽  
Author(s):  
Fred C. Adams ◽  
Katherine Freese
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Inflationary Models

The BICEP2 data and a single Higgs-like interacting scalar field

2014 ◽  
Vol 23 (09) ◽  
pp. 1450075 ◽  
Author(s):  
Murli Manohar Verma ◽  
Shankar Dayal Pathak
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Gravity Waves ◽  
Field Potential ◽  
Thermodynamical Equilibrium ◽  
Conservation Of Energy ◽  
Order Of Magnitude ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Perturbed Equation

It is proposed that the recently announced BICEP2 value of tensor-to-scalar ratio r ~ 0.2 can be explained as containing an extra contribution from the recent acceleration of the universe. In fact this contribution, being robust, recent and of much longer duration (by a large order of magnitude) may dominate the contribution from the inflationary origin. In a possible scenario, matter (dark or baryonic) and radiation etc. can emerge from a single Higgs-like tachyonic scalar field in the universe through a physical mechanism not yet fully known to us. The components interact among themselves to achieve the thermodynamical equilibrium in the evolution of the universe. The field potential for the present acceleration of the universe would give a boost to the amplitude of the tensor fluctuations of gravity waves generated by the early inflation and the net effects may be higher than the earlier Planck bounds. In the process, the dark energy, as a cosmological constant decays into creation of dark matter. The diagnostics for the three-component, spatially homogeneous tachyonic scalar field are discussed in detail. The components of the field with perturbed equation of state (EoS) are taken to interact mutually and the conservation of energy for individual components gets violated. We study mainly the Om(x) diagnostics with the observed set of H(z) values at various redshifts, and the dimensionless statefinders for these interacting components. This analysis provides a strong case for the interacting dark energy in our model.

scholarly journals Condensation of a scalar field non-minimally coupled to gravity in a cosmological context

2020 ◽  
Vol 35 (32) ◽  
pp. 2050270
Author(s):  
Amir Ghalee
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Condensed Phase ◽  
Condensed State ◽  
De Sitter ◽  
Cosmological Perturbations ◽  
Cosmological Context ◽  
Background Density ◽  
The Universe ◽  
Bonnet Term

We present a new mechanism to condense a scalar field coupled to the Gauss–Bonnet term. We propose a scenario in which the condensed state will emerge from the background energy density in the late-Universe. During the radiation and dust-dominated eras, the energy density of the scalar field, [Formula: see text], decreases at a slower rate than the background density. Eventually, [Formula: see text] dominates over the energy density of dust and the scalar field could be condensed. In the condensed phase, we have the de Sitter phase for the universe with [Formula: see text]. Moreover, we study the cosmological perturbations of the model and explore predictions of the model.

scholarly journals Quantum Cosmologies Under Geometrical Unification of Gravity and Dark Energy

Symmetry ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 860 ◽  
Author(s):  
Carlos A. Rubio ◽  
Felipe A. Asenjo ◽  
Sergio A. Hojman
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Field Potential ◽  
Constraint Equation ◽  
Spinless Particle ◽  
Quantization Scheme ◽  
Dynamical Equations ◽  
Order Constraint ◽  
The Universe ◽  
Friedmann Robertson Walker

A Friedmann–Robertson–Walker Universe was studied with a dark energy component represented by a quintessence field. The Lagrangian for this system, hereafter called the Friedmann–Robertson–Walker–quintessence (FRWq) system, was presented. It was shown that the classical Lagrangian reproduces the usual two (second order) dynamical equations for the radius of the Universe and for the quintessence scalar field, as well as a (first order) constraint equation. Our approach naturally unified gravity and dark energy, as it was obtained that the Lagrangian and the equations of motion are those of a relativistic particle moving on a two-dimensional, conformally flat spacetime. The conformal metric factor was related to the dark energy scalar field potential. We proceeded to quantize the system in three different schemes. First, we assumed the Universe was a spinless particle (as it is common in literature), obtaining a quantum theory for a Universe described by the Klein–Gordon equation. Second, we pushed the quantization scheme further, assuming the Universe as a Dirac particle, and therefore constructing its corresponding Dirac and Majorana theories. With the different theories, we calculated the expected values for the scale factor of the Universe. They depend on the type of quantization scheme used. The differences between the Dirac and Majorana schemes are highlighted here. The implications of the different quantization procedures are discussed. Finally, the possible consequences for a multiverse theory of the Dirac and Majorana quantized Universe are briefly considered.

Constraints on the scalar-field potential in inflationary models

1991 ◽  
Vol 43 (4) ◽  
pp. 965-976 ◽  
Author(s):  
Fred C. Adams ◽  
Katherine Freese ◽  
Alan H. Guth
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Inflationary Models
Sign in / Sign up

Export Citation Format

Share Document