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 Inflationary cosmology in unimodular F(T) gravity

2017 ◽  
Vol 32 (21) ◽  
pp. 1750114 ◽  
Author(s):  
Kazuharu Bamba ◽  
Sergei D. Odintsov ◽  
Emmanuel N. Saridakis
Keyword(s):  
Spectral Index ◽  
Teleparallel Gravity ◽  
Specific Model ◽  
Inflationary Cosmology ◽  
Model Parameters ◽  
De Sitter ◽  
Reconstruction Procedure ◽  
Additional Advantage ◽  
Slow Roll ◽  
Good Agreement

We investigate the inflationary realization in the context of unimodular F(T) gravity, which is based on the F(T) modification of teleparallel gravity, in which one imposes the unimodular condition through the use of Lagrange multipliers. We develop the general reconstruction procedure of the F(T) form that can give rise to a given scale-factor evolution, and then we apply it in the inflationary regime. We extract the Hubble slow-roll parameters that allow us to calculate various inflation-related observables, such as the scalar spectral index and its running, the tensor-to-scalar ratio, and the tensor spectral index. Then, we examine the particular cases of de Sitter and power-law inflation, of Starobinsky inflation, as well as inflation in a specific model of unimodular F(T) gravity. As we show, in all cases the predictions of our scenarios are in a very good agreement with Planck observational data. Finally, inflation in unimodular F(T) gravity has the additional advantage that it always allows for a graceful exit for specific regions of the model parameters.

scholarly journals Phenomenology analysis of duration inflation for tachyon field in loop quantum cosmology

2014 ◽  
Vol 23 (11) ◽  
pp. 1450087 ◽  
Author(s):  
Kui Xiao ◽  
Xiao-Kai He ◽  
Fei Huang ◽  
Jian-Yang Zhu
Keyword(s):  
Quantum Cosmology ◽  
Initial Conditions ◽  
Scale Factor ◽  
Loop Quantum Cosmology ◽  
Tachyon Field ◽  
Exponential Potential ◽  
Quadratic Potential ◽  
Slow Rolling

Assuming that the e-folding number is just determined by the change of the scale factor, the tachyonic inflation theory in loop quantum cosmology (LQC) has been discussed. Considering the tachyon field with exponential potential and inverse quadratic potential, we find that the evolutionary pictures of super inflation are affected by the potentials and the initial conditions. However it cannot provide enough e-folding number, no matter which condition is chosen. Therefore a slow-rolling inflation is necessary. The e-folding number for slow-rolling inflation depends on the values of the parameter α of the exponential potential and the initial conditions. To get enough e-folding number, α should be small. Based on the slow-rolling inflation happens immediately when the super inflation ends, and the scale factor continuously grows during the whole inflation stage, we consider an e-folding number provided by the whole inflationary stage, and we find that it is easier to get enough e-folding number when the scale factor increases during all the inflation phase.

scholarly journals WMAP5 OBSERVATIONAL CONSTRAINTS ON BRANEWORLD NEW INFLATION MODEL

2010 ◽  
Vol 25 (01) ◽  
pp. 171-183 ◽  
Author(s):  
R. ZARROUKI ◽  
Z. SAKHI ◽  
M. BENNAI
Keyword(s):  
High Energy ◽  
Observational Constraints ◽  
Type Ii ◽  
Energy Limit ◽  
High Energy Limit ◽  
Inflation Model ◽  
Slow Roll ◽  
Braneworld Model ◽  
Perturbation Spectrum ◽  
Good Agreement

We study a new inflation potential in the framework of the Randall–Sundrum type II braneworld model. Using the technic developed in Ref. 1, we consider both a monomial and a new inflation potentials and apply the slow-roll approximation in high energy limit, to derive analytical expression of relevant perturbation spectrum. We show that for some values of the parameter n in the potential [Formula: see text] we obtain a perturbation spectrum which gives a good agreement with the recent WMAP5 observations.

Tachyon-inspired viscous inflation using Hamilton–Jacobi’s formalism during high dissipative regime

2019 ◽  
Vol 28 (11) ◽  
pp. 1950136 ◽  
Author(s):  
Rabia Saleem
Keyword(s):  
Detailed Analysis ◽  
Model Parameters ◽  
Inflationary Model ◽  
Tachyon Field ◽  
Astrophysical Data ◽  
Slow Roll ◽  
Acceptable Range

This paper deals with warm viscous inflation inspired by tachyon field using an important inflationary method known as Hamilton–Jacobi’s Formalism. This method provides a way to solve the equations of inflationary model without using extra approximations other than slow-roll. In this scenario, a general inflationary formalism is developed for tachyon field and the work is restricted to high dissipative regime. A detailed analysis of the model is presented for three different cases of constant as well as variable bulk and dissipative coefficients. In each case, the model parameters are constrained to plot the physically acceptable range of the perturbed parameters. The parametric trajectories proved that the acquired results for all cases are compatible with Planck astrophysical data.

scholarly journals Observational constraints on the generalized α attractor model

2018 ◽  
Vol 27 (05) ◽  
pp. 1850058 ◽  
Author(s):  
M. Shahalam ◽  
Ratbay Myrzakulov ◽  
Shynaray Myrzakul ◽  
Anzhong Wang
Keyword(s):  
Cosmic Acceleration ◽  
Asymptotic Region ◽  
Model Parameters ◽  
Observational Constraints ◽  
Late Time ◽  
Freezing And Thawing ◽  
Energy Models ◽  
Slow Roll ◽  
Attractor Model ◽  
Original Potential

We study the generalized [Formula: see text] attractor model in the context of the late time cosmic acceleration. The model interpolates between the scaling freezing and thawing dark energy models. In the slow roll region, the original potential is modified whereas the modification ceases in the asymptotic region and the effective potential behaves as the quadratic one. In our setting, the field rolls slowly around the present epoch and mimics the scaling behavior in the future. We obtain observational constraints on the model parameters by using an integrated database (SN+Hubble+BAO+CMB).

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 Generalization of cosmological attractor approach to Einstein–Gauss–Bonnet gravity

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Ekaterina O. Pozdeeva
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Leading Order ◽  
Bonnet Gravity ◽  
Inflationary Scenario ◽  
Slow Roll ◽  
Inflationary Parameters ◽  
Bonnet Term ◽  
Scalar Perturbations ◽  
Good Agreement

Abstract We construct models with the Gauss–Bonnet term multiplied by a function of the scalar field leading to an inflationary scenario. The consideration is related to the slow-roll approximation. The cosmological attractor approach gives the spectral index of scalar perturbations which is in a good agreement with modern observation and allows for variability of the tensor-to-scalar ratio. We reconstruct models with variability of parameters, which allows one to reproduce cosmological attractor predictions for inflationary parameters in an approximation of the leading order of 1/N in Einstein–Gauss–Bonnet gravity.

Investigating the vibrational behaviour of a rotating two-blade propeller by using a self-tracking method

2018 ◽  
Vol 233 (3) ◽  
pp. 835-847 ◽  
Author(s):  
Mohammad-Reza Ashory ◽  
Farhad Talebi ◽  
Heydar R Ghadikolaei ◽  
Morad Karimpour
Keyword(s):  
Natural Frequency ◽  
Measurement Errors ◽  
Mode Shapes ◽  
Model Parameters ◽  
Test Results ◽  
Modal Assurance Criterion ◽  
Tracking Method ◽  
Strong Resemblance ◽  
Test Scenarios ◽  
Good Agreement

This study investigated the vibrational behaviour of a rotating two-blade propeller at different rotational speeds by using self-tracking laser Doppler vibrometry. Given that a self-tracking method necessitates the accurate adjustment of test setups to reduce measurement errors, a test table with sufficient rigidity was designed and built to enable the adjustment and repair of test components. The results of the self-tracking test on the rotating propeller indicated an increase in natural frequency and a decrease in the amplitude of normalized mode shapes as rotational speed increases. To assess the test results, a numerical model created in ABAQUS was used. The model parameters were tuned in such a way that the natural frequency and associated mode shapes were in good agreement with those derived using a hammer test on a stationary propeller. The mode shapes obtained from the hammer test and the numerical (ABAQUS) modelling were compared using the modal assurance criterion. The examination indicated a strong resemblance between the hammer test results and the numerical findings. Hence, the model can be employed to determine the other mechanical properties of two-blade propellers in test scenarios.

scholarly journals Thermal conductivity of unsaturated clay-rocks

2010 ◽  
Vol 14 (1) ◽  
pp. 91-98 ◽  
Author(s):  
D. Jougnot ◽  
A. Revil
Keyword(s):  
Thermal Conductivity ◽  
Porous Material ◽  
Solid Phase ◽  
Model Parameters ◽  
Electrical Parameters ◽  
New Model ◽  
Unsaturated Clay ◽  
Unsaturated Porous Material ◽  
Clay Rocks ◽  
Good Agreement

Abstract. The parameters used to describe the electrical conductivity of a porous material can be used to describe also its thermal conductivity. A new relationship is developed to connect the thermal conductivity of an unsaturated porous material to the thermal conductivity of the different phases of the composite, and two electrical parameters called the first and second Archie's exponents. A good agreement is obtained between the new model and thermal conductivity measurements performed using packs of glass beads and core samples of the Callovo-Oxfordian clay-rocks at different saturations of the water phase. We showed that the three model parameters optimised to fit the new model against experimental data (namely the thermal conductivity of the solid phase and the two Archie's exponents) are consistent with independent estimates. We also observed that the anisotropy of the effective thermal conductivity of the Callovo-Oxfordian clay-rock was mainly due to the anisotropy of the thermal conductivity of the solid phase.

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