scholarly journals Slow-roll inflation with exponential potential in scalar-tensor models

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
L. N. Granda ◽  
D. F. Jimenez
Keyword(s):  
Scalar Field ◽  
Order Approximation ◽  
Energy Scale ◽  
Model Parameters ◽  
Exponential Potential ◽  
Minimal Coupling ◽  
Slow Roll ◽  
Special Cases ◽  
First Order Approximation ◽  
Slow Roll Inflation

Abstract A study of the slow-roll inflation for an exponential potential in the frame of the scalar-tensor theory is performed, where non-minimal kinetic coupling to curvature and non-minimal coupling of the scalar field to the Gauss-Bonnet invariant are considered. Different models were considered with couplings given by exponential functions of the scalar field, that lead to graceful exit from inflation and give values of the scalar spectral index and the tensor-to-scalar ratio in the region bounded by the current observational data. Special cases were found, where the coupling functions are inverse of the potential, that lead to inflation with constant slow-roll parameters, and it was possible to reconstruct the model parameters for given ns and r. In first-order approximation the standard consistency relation maintains its validity in the model with non-minimal coupling, but it modifies in presence of Gauss–Bonnet coupling. The obtained Hubble parameter during inflation, $$H\sim 10^{-5} M_p$$H∼10-5Mp and the energy scale of inflation $$V^{1/4}\sim 10^{-3} M_p$$V1/4∼10-3Mp, are consistent with the upper bounds set by latest observations.

scholarly journals Inflation and supersymmetry breaking in Higgs-R2 supergravity

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Shuntaro Aoki ◽  
Hyun Min Lee ◽  
Adriana G. Menkara
Keyword(s):  
Supersymmetry Breaking ◽  
Planck Scale ◽  
Scalar Fields ◽  
Minimal Coupling ◽  
Slow Roll ◽  
New Construction ◽  
Visible Sector ◽  
Higgs Fields ◽  
Chiral Superfields ◽  
Slow Roll Inflation

Abstract We propose a new construction of the supergravity inflation as an UV completion of the Higgs-R2 inflation. In the dual description of R2-supergravity, we show that there appear dual chiral superfields containing the scalaron or sigma field in the Starobinsky inflation, which unitarizes the supersymmetric Higgs inflation with a large non-minimal coupling up to the Planck scale. We find that a successful slow-roll inflation is achievable in the Higgs-sigma field space, but under the condition that higher curvature terms are introduced to cure the tachyonic mass problems for spectator singlet scalar fields. We also discuss supersymmetry breaking and its transmission to the visible sector as a result of the couplings of the dual chiral superfields and the non-minimal gravity coupling of the Higgs fields.

scholarly journals Tachyonic matter cosmology with exponential and hyperbolic potentials

2017 ◽  
Vol 26 (02) ◽  
pp. 1750012 ◽  
Author(s):  
B. Pourhassan ◽  
J. Naji
Keyword(s):  
Scalar Field ◽  
Observational Data ◽  
Cosmological Parameters ◽  
Field Potentials ◽  
Exponential Potential ◽  
Frw Universe ◽  
Hyperbolic Cosine ◽  
Special Cases ◽  
Friedmann Robertson Walker ◽  
Type Potential

In this paper, we consider tachyonic matter in spatially flat Friedmann–Robertson–Walker (FRW) universe, and obtain behavior of some important cosmological parameters for two special cases of potentials. First, we assume the exponential potential and then consider hyperbolic cosine type potential. In both cases, we obtain behavior of the Hubble, deceleration and EoS parameters. Comparison with observational data suggest the model with hyperbolic cosine type scalar field potentials has good model to describe universe.

scholarly journals General Slow-Roll Inflation in f(R) Gravity under the Palatini Approach

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 1958
Author(s):  
Sabit Bekov ◽  
Kairat Myrzakulov ◽  
Ratbay Myrzakulov ◽  
Diego Sáez-Chillón Gómez
Keyword(s):  
Scalar Field ◽  
Simple Model ◽  
Spectral Index ◽  
Effective Potential ◽  
Modified Gravity ◽  
Palatini Formalism ◽  
Slow Roll ◽  
Slow Roll Inflation

Slow-roll inflation is analyzed in the context of modified gravity within the Palatini formalism. As shown in the literature, inflation in this framework requires the presence of non-traceless matter; otherwise, it does not occur just as a consequence of the nonlinear gravitational terms of the action. Nevertheless, by including a single scalar field that plays the role of the inflaton, slow-roll inflation can be performed in these theories, where the equations lead to an effective potential that modifies the dynamics. We obtain the general slow-roll parameters and analyze a simple model to illustrate the differences introduced by the gravitational terms under the Palatini approach, and the modifications on the spectral index and the tensor to scalar ratio predicted by the model.

scholarly journals LARGE NON-GAUSSIANITY FROM MULTI-BRID INFLATION

2011 ◽  
Vol 01 ◽  
pp. 108-113
Author(s):  
ATSUSHI NARUKO ◽  
MISAO SASAKI
Keyword(s):  
Scalar Field ◽  
General Feature ◽  
Present Model ◽  
The Other ◽  
Model Parameters ◽  
Exponential Potential ◽  
Inflation Model ◽  
Hybrid Inflation ◽  
Non Gaussian ◽  
Near Future

A model of multi-component hybrid inflation, dubbed multi-brid inflation, which may yield a large non-Gaussian paramter fNL, was proposed recently. In particular, for a two-brid inflation model with an exponential potential and the condition that the end of inflation is an ellipse in the field space, it was found that, while keeping the other observational quantities within the range consistent with observations, large non-Gaussianity is possible for certain inflationary trajectories. In this talk, in order to see if this result is a general feature of multi-brid inflation, we consider a model with a potential with an exponent quadratic in the scalar field components. We also consider a more general class of ellipses for the end of inflation. Focusing on the case of two-brid inflation, we find that large non-Gaussianity is also possible in the present model. Then by tuning the model parameters, we find that there exist models for which both the non-Gaussianity and the tensor-to-scalar ratio are large enough to be detected in the very near future.

scholarly journals THE POSSIBILITY OF INFLATION IN ASYMPTOTICALLY SAFE GRAVITY

2012 ◽  
Vol 21 (07) ◽  
pp. 1250062 ◽  
Author(s):  
SUNGWOOK E. HONG ◽  
YOUNG JAE LEE ◽  
HEESEUNG ZOE
Keyword(s):  
Phase Space ◽  
Critical Point ◽  
Hubble Parameter ◽  
Relative Energy ◽  
Energy Scale ◽  
Einstein Frame ◽  
Coupling Constants ◽  
Slow Roll ◽  
Slow Roll Inflation

We examine the inflationary modes in the cubic curvature theories in the context of asymptotically safe gravity. On the phase space of the Hubble parameter, there exists a critical point which corresponds to the slow-roll inflation in Einstein frame. Most of the e-foldings are attained around the critical point for each inflationary trajectories. If the coupling constants gi have the parametric relations generated as the power of the relative energy scale of inflation H0 to the cutoff Λ, a successful inflation with more than 60 e-foldings occurs near the critical point.

LENGTH OF INFLATION AND NON-GAUSSIANITY

2011 ◽  
Vol 20 (03) ◽  
pp. 361-370
Author(s):  
SHIRO HIRAI ◽  
TOMOYUKI TAKAMI
Keyword(s):  
Nonlinearity Parameter ◽  
Slow Roll ◽  
Higher Derivative ◽  
Scalar Matter ◽  
Special Cases ◽  
Slow Roll Inflation

Certain inflation models are shown to have large non-Gaussianity in special cases. Namely, slow-roll inflation models with an effective higher derivative interaction, in which the length of inflation is finite and a scalar-matter-dominated period or power inflation is adopted as pre-inflation, are considered. Using Holman and Tolley's formula of the nonlinearity parameter in the flattened triangle configurations [Formula: see text], we calculate the value of [Formula: see text]. The value of [Formula: see text] is found to be largest [Formula: see text] when the inflation length is approximately 60 e-folds, and [Formula: see text] is found to depend strongly on the length of inflation and the cut-off scale.

scholarly journals Dynamical System Perspective of Cosmological Models Minimally Coupled with Scalar Field

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
S. Surendra Singh ◽  
Chingtham Sonia
Keyword(s):  
Dynamical System ◽  
Scalar Field ◽  
Fixed Points ◽  
Cosmic Acceleration ◽  
Stable Model ◽  
Exponential Potential ◽  
Total Energy Density ◽  
System Perspective ◽  
Special Cases ◽  
Potential Form

The stability criteria for the dynamical system of a homogeneous and isotropic cosmological model are investigated with the interaction of a scalar field in the presence of a perfect fluid. In this paper, we depict the dynamical system perspective to study qualitatively the scalar field cosmology under two special cases, with and without potential. In the absence of potential, we get a two-dimensional dynamical system, and we study the analytical as well as geometrical behavior. For the dynamical system with potential, we analyze different potential forms: simple exponential potential form (Vϕ=Voe−λϕ), double exponential potential form Vϕ=Voexp−Aexp2αϕ, and inverse power law potential form (Vϕ=Voϕ−α). We generate an autonomous system of ordinary differential equations (ASODE) for each case by introducing new dimensionless variables and obtain respective fixed points. We also analyze the type, nature, and stability of the fixed points and how their behavior reflects towards the cosmological scenarios. Throughout the whole work, the investigation of this model has shown us the deep connection between these theories and cosmic acceleration phenomena. The phase plots of the system at different conditions and different values of γ have been analyzed in detail, and their geometrical interpretations have been studied. The perturbation plots of the dynamical system have been analyzed with emphasis on our analytical findings. We have evaluated the total energy density (Ωϕ) at the fixed points and also found out the suitable range of γ and λ for a stable model.

scholarly journals Induced gravity effect on inflationary parameters in a holographic cosmology

2020 ◽  
Vol 29 (02) ◽  
pp. 2050010 ◽  
Author(s):  
Aatifa Bargach ◽  
Farida Bargach ◽  
Ahmed Errahmani ◽  
Taoufik Ouali
Keyword(s):  
Model Parameters ◽  
Observational Constraints ◽  
Tachyon Field ◽  
Exponential Potential ◽  
Quadratic Potential ◽  
Induced Gravity ◽  
Slow Roll ◽  
Inflationary Parameters ◽  
Correction Terms ◽  
Good Agreement

We investigate the observational constraints on inflationary parameters in the context of a holographic cosmology with an induced gravity correction. We consider two situations where a universe is first filled with a scalar field and second with a tachyon field. Both cases are investigated in a slow-roll regime. We adopt a quadratic potential and an exponential potential for the scalar and the tachyon inflation, respectively. In this regard, the standard background and perturbative parameters characterizing the inflationary era are modified by correction terms. We show a good agreement between theoretical model parameters and Planck2018 observational data for both scalar and tachyon fields.

scholarly journals Non-minimal tinges of Unimodular Gravity

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Mario Herrero-Valea ◽  
Raquel Santos-Garcia
Keyword(s):  
General Relativity ◽  
Renormalization Group ◽  
Scalar Field ◽  
Path Integral ◽  
Energy Scale ◽  
Quantum Corrections ◽  
Renormalization Group Flow ◽  
Path Integral Formulation ◽  
Minimal Coupling ◽  
Group Flow

Abstract Unimodular Gravity is normally assumed to be equivalent to General Relativity for all matters but the character of the Cosmological Constant. Here we discuss this equivalence in the presence of a non-minimally coupled scalar field. We show that when we consider gravitation to be dynamical in a QFT sense, quantum corrections can distinguish both theories if the non-minimal coupling is non-vanishing. In order to show this, we construct a path integral formulation of Unimodular Gravity, fixing the complicated gauge invariance of the theory and computing all one-loop divergences. We find a combination of the couplings in the Lagrangian to which we can assign a physical meaning. It tells whether quantum gravitational phenomena can be ignored or not at a given energy scale. Its renormalization group flow differs depending on if it is computed in General Relativity or Unimodular Gravity.

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