Cosmological inflationary studying around the type IV singularity within f(T) gravity

2020 ◽  
Vol 17 (14) ◽  
pp. 2050195
Author(s):  
M. G. Ganiou ◽  
M. J. S. Houndjo ◽  
H. F. Abadji ◽  
J. Tossa
Keyword(s):  
Dynamical Instability ◽  
Theoretical Formula ◽  
Inflationary Universe ◽  
Late Time ◽  
De Sitter ◽  
Type Iv ◽  
Flow Parameters ◽  
Additional Constant ◽  
Text Model ◽  
Hubble Flow

In this paper, we investigate the effects of Type IV singularity through [Formula: see text] gravity description of inflationary Universe, where [Formula: see text] denotes the torsion scalar. With the Friedmann equations of the theory, we reconstruct a [Formula: see text] model according to a given Hubble rate susceptible to describe the inflationary era near the Type IV singularity. One obtains an interesting well-known [Formula: see text] model but with additional constant parameter [Formula: see text] staying as the Type IV singularity contribution. Moreover, we calculate the Hubble flow parameters in order to determine the dynamical evolution of the cosmological system. The results show that some of the Hubble flow parameters are small near the Type IV singularity and become singular at Type IV singularity, indicating that a dynamical instability of the cosmological system occurs at that point. This means that the dynamical cosmological evolution up to that point ceases to be the final attractor since the system is abruptly interrupted. Furthermore, by considering the [Formula: see text] trace anomaly equation, the previous result on the Type IV singularity is consolidated by the conditional instability coming from the de Sitter inflationary description of the reconstructed [Formula: see text] model. The model leads to instability strongly governed by the Type IV singularity parameter [Formula: see text] is viewed as the graceful exit from inflation. Our theoretical [Formula: see text] description based on slow-roll parameters not only confirms some observational data on spectral index and the scalar-to-tensor ratio from Planck data and BICEP[Formula: see text]/Keck-Array data, but also shows the property of [Formula: see text] gravity in describing the early and late-time evolution of our Universe.

scholarly journals FROM DE SITTER TO DE SITTER: A NON-SINGULAR INFLATIONARY UNIVERSE DRIVEN BY VACUUM

2006 ◽  
Vol 15 (12) ◽  
pp. 2241-2247 ◽  
Author(s):  
SAULO CARNEIRO
Keyword(s):  
Vacuum Energy ◽  
Cosmological Solution ◽  
Inflationary Universe ◽  
Late Time ◽  
De Sitter ◽  
Classical Analysis ◽  
Huge Amount ◽  
Matter Production ◽  
The Standard Model ◽  
De Sitter Universe

A semi-classical analysis of vacuum energy in the expanding space–time suggests that the cosmological term decays with time, with a concomitant matter production. For early times we find, in Planck units, Λ ≈ H4, where H is the Hubble parameter. The corresponding cosmological solution has no initial singularity, existing since an infinite past. During an infinitely long period we have a quasi-de Sitter, inflationary universe, with H ≈ 1. However, at a given time, the expansion undertakes a phase transition, with H and Λ decreasing to nearly zero in a few Planck times, producing a huge amount of radiation. On the other hand, the late-time scenario is similar to the standard model, with the radiation phase followed by a dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again.

Inflationary dynamics in f(𝒢) gravity

2017 ◽  
Vol 26 (04) ◽  
pp. 1750030 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Power Spectrum ◽  
Universe Model ◽  
De Sitter ◽  
Slow Roll ◽  
Homogeneous Universe ◽  
Text Model ◽  
Flow Functions ◽  
Hubble Flow

This paper investigates inflationary dynamics for isotropic and homogeneous universe model in the background of [Formula: see text] gravity. We construct Hubble-flow functions, slow-roll parameters, amplitude of scalar power spectrum, spectral index and tensor–scalar ratio for a particular form of equation of state which describes quasi-de Sitter expansion. The dynamics of inflationary epoch is analyzed for scalar field as well as fluid cosmology with viable power-law [Formula: see text] model. We obtain different potential functions that correspond to chaotic inflation and Starobinsky type models. The graphical behavior of these parameters shows compatible results with observational Planck 2015 data in this gravity.

scholarly journals Type IV singular bouncing cosmology from f(T) gravity

2019 ◽  
Vol 28 (11) ◽  
pp. 1950147
Author(s):  
P. H. Logbo ◽  
M. J. S. Houndjo
Keyword(s):  
Stability Analysis ◽  
Dynamical Evolution ◽  
Dynamical Instability ◽  
Type Iv ◽  
Bouncing Cosmology ◽  
Slow Roll ◽  
Singularity Point ◽  
Text Model ◽  
The Stability ◽  
Modified Formula

We investigate bouncing scenario in the modified [Formula: see text] gravity, [Formula: see text] being the torsion scalar. Attention is attached to the reconstruction of [Formula: see text] able to describe type IV singular bouncing evolution, where we adopt as assumption that the bouncing and type IV singularity points coincide. In the context of the reconstructed [Formula: see text] model, we calculate the Hubble slow-roll parameters in order to determine the dynamical evolution of the cosmological system under study. The results show that the Hubble slow-roll parameters become singular at the type IV singularity indicating a dynamical instability. Moreover, we perform the stability analysis of the [Formula: see text] gravity solution where, according to the obtained result, the type IV singularity point is a saddle point in agreement with the bounce scenario.

scholarly journals Unitarity at the late time boundary of de Sitter

2020 ◽  
Vol 2020 (6) ◽  
Author(s):  
Gizem Şengör ◽  
Constantinos Skordis
Keyword(s):  
Late Time ◽  
De Sitter ◽  
Time Boundary

PRIMORDIAL BLACK HOLE PAIR CREATION IN R2 THEORY

1998 ◽  
Vol 13 (28) ◽  
pp. 2289-2293 ◽  
Author(s):  
B. C. PAUL ◽  
S. MUKHERJEE ◽  
G. P. SINGH ◽  
A. BEESHAM
Keyword(s):  
Black Holes ◽  
Semiclassical Approximation ◽  
Pair Creation ◽  
Quadratic Term ◽  
Inflationary Universe ◽  
Primordial Black Hole ◽  
Primordial Black Holes ◽  
De Sitter ◽  
Gravitational Action ◽  
Spatial Section

The probability for quantum creation of an inflationary universe with a pair of black holes has been studied in semiclassical approximation with Hartle–Hawking boundary conditions, assuming a gravitational action which includes a quadratic term in the scalar curvature αR2, α being a constant. The action of the instanton responsible for creating such a universe, with a spatial section with S1×S2 topology, is seen to be less than that of a de Sitter S3 instanton, unless α<-1/(8Λ), where Λ is the cosmological constant. Since negative α implies a classical instability, the probability for production of primordial black holes seems to be suppressd in R2-theory.

Constraints on kinematic model from Pantheon SNIa, OHD and CMB shift parameter measurements

2021 ◽  
Vol 36 (08) ◽  
pp. 2150049
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Confidence Region ◽  
Kinematic Model ◽  
Hubble Constant ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Shift Parameter ◽  
Redshift Range ◽  
Data Points ◽  
Text Model ◽  
Good Agreement

In this paper, we reconstruct the late-time cosmological dynamics using a purely kinematic approach. In particular, considering a divergence-free parametrization for deceleration parameter [Formula: see text], we first derive the jerk parameter [Formula: see text] and then confront it with combination of various cosmological datasets. We use the most recent observational datasets consisting of the 1048 Pantheon Supernovae Ia data points in the redshift range [Formula: see text], the 51 data points of observational Hubble parameter (OHD) measurements in the redshift range [Formula: see text], the Hubble constant [Formula: see text] (R19) and the CMB shift parameter measurements. We study the evolution of different cosmological quantities for the present model and compare it with the concordance [Formula: see text]CDM model. We find that only the combined Pantheon+OHD+R19 data shows good agreement with the [Formula: see text]CDM [Formula: see text] model within [Formula: see text] confidence region. We also find that our model successfully generates late time cosmic acceleration along with a decelerated expansion in the past.

scholarly journals Late-time quantum radiation by a uniformly accelerated detector in de Sitter spacetime

2018 ◽  
Vol 98 (10) ◽  
Author(s):  
Shumpei Yamaguchi ◽  
Rumi Tatsukawa ◽  
Shih-Yuin Lin ◽  
Kazuhiro Yamamoto
Keyword(s):  
Late Time ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime ◽  
Quantum Radiation ◽  
Time Quantum

scholarly journals Averaging generalized scalar field cosmologies II: locally rotationally symmetric Bianchi I and flat Friedmann–Lemaître–Robertson–Walker models

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
Genly Leon ◽  
Sebastián Cuéllar ◽  
Esteban González ◽  
Samuel Lepe ◽  
Claudio Michea ◽  
...  
Keyword(s):  
Scalar Field ◽  
Nonlinear Dynamical Systems ◽  
Perturbation Parameter ◽  
Time Dependent ◽  
Late Time ◽  
De Sitter ◽  
Time Dynamics ◽  
Locally Rotationally Symmetric ◽  
Bianchi I ◽  
Rotationally Symmetric

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.

scholarly journals Building models of inflation in no-scale supergravity

2020 ◽  
pp. 2030011
Author(s):  
John Ellis ◽  
Marcos A. G. García ◽  
Natsumi Nagata ◽  
Dimitri V. Nanopoulos ◽  
Keith A. Olive ◽  
...  
Keyword(s):  
Cold Dark Matter ◽  
Planck Scale ◽  
Neutrino Masses ◽  
De Sitter ◽  
Building Models ◽  
Scale Models ◽  
Cosmological Inflation ◽  
Text Model ◽  
Hilbert Action ◽  
Scalar Perturbations

After reviewing the motivations for cosmological inflation formulated in the formalism of supersymmetry, we argue that the appropriate framework is that of no-scale supergravity. We then show how to construct within this framework inflationary models whose predictions for the tilt in the spectrum of scalar perturbations, [Formula: see text], and the ratio, [Formula: see text], of tensor and scalar perturbations coincide with those of the [Formula: see text] model of inflation proposed by Starobinsky. A more detailed study of no-scale supergravity reveals a structure that is closely related to that of [Formula: see text] modifications of the minimal Einstein–Hilbert action for general relativity, opening avenues for constructing no-scale de Sitter and anti-de Sitter models by combining pairs of Minkowski models, as well as generalizations of the original no-scale Starobinsky models of inflation. We then discuss the phenomenology of no-scale models of inflation, including inflaton decay and reheating, and then the construction of explicit scenarios based on SU(5), SO(10) and string-motivated flipped SU(5)×U(1) GUT models. The latter provides a possible model of almost everything below the Planck scale, including neutrino masses and oscillations, the cosmological baryon asymmetry and cold dark matter, as well as [Formula: see text] and [Formula: see text].

scholarly journals MODIFIED GRAVITATIONAL THEORIES AND COSMIC ACCELERATION

2004 ◽  
Vol 19 (31) ◽  
pp. 5343-5350 ◽  
Author(s):  
DAMIEN A. EASSON
Keyword(s):  
Dark Energy ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Gravitational Theories ◽  
Hilbert Action

Modified gravitational theories can provide alternatives to dark energy as an explaination for the observed late-time cosmic acceleration. Several examples of low-curvature corrections to the Einstein-Hilbert action are studied. These models generically contain unstable de Sitter solutions and, depending on the parameters of the theory, can exhibit late time accelerating attractor solutions.

Sign in / Sign up

Export Citation Format

Share Document