scholarly journals α-Attractors and reheating in a nonminimal inflationary model

2020 ◽  
Vol 29 (10) ◽  
pp. 2050077
Author(s):  
R. Shojaee ◽  
K. Nozari ◽  
F. Darabi
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Parameter Space ◽  
Model Potential ◽  
Index Formula ◽  
Inflationary Model ◽  
Scalar Spectral Index ◽  
Canonical Scalar Field

We study [Formula: see text]-attractor models with both E-model and T-model potential in an extended Nonminimal Derivative (NMD) inflation where a canonical scalar field and its derivatives are nonminimally coupled to gravity. We calculate the evolution of perturbations during this regime. Then by adopting inflation potentials of the model we show that in the large [Formula: see text] and small [Formula: see text] limit, the value of the scalar spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text] are universal. Next, we study reheating after inflation in this formalism. We obtain some constraints on the model’s parameter space by adopting the results with Planck 2018.

scholarly journals WHAT IF THE INFLATON IS A SPINOR CONDENSATE?

2009 ◽  
Vol 18 (14) ◽  
pp. 2173-2179 ◽  
Author(s):  
S. SHANKARANARAYANAN
Keyword(s):  
Scalar Field ◽  
Gravitational Wave ◽  
Spectral Index ◽  
Spinor Condensate ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
The Future ◽  
Wmap Data ◽  
Elementary Field ◽  
Canonical Scalar Field

In the usual cosmological inflationary scenarios, the scalar field — the inflaton — is usually assumed to be an elementary field. In this essay, we ask: What are the observational signatures if the scalar field is a spinor condensate? And is there a way to distinguish between the canonical scalar field and the spinor-condensate-driven models? In the homogeneous and isotropic background, we show that — although the dark-spinor (Elko) condensate leads to an acceleration equation identical to that of the canonical-scalar-field-driven inflation — the dynamics of the two models are different. In the slow-roll limit, we show that the model predicts a running of the scalar spectral index consistent with the WMAP data. We show that the consistency relations between the spinor condensate and the canonical-scalar-field-driven model are different, which we will be able to test using the future CMB and gravitational wave missions.

scholarly journals Fab Four: When John and George Play Gravitation and Cosmology

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
J.-P. Bruneton ◽  
M. Rinaldi ◽  
A. Kanfon ◽  
A. Hees ◽  
S. Schlögel ◽  
...  
Keyword(s):  
Scalar Field ◽  
Solar System ◽  
Parameter Space ◽  
Ad Hoc ◽  
Initial Conditions ◽  
Equations Of Motion ◽  
Inflationary Model ◽  
Einstein Tensor ◽  
Chameleon Mechanism ◽  
Derivatives Of

Scalar-tensor theories of gravitation attract again a great interest since the discovery of the Chameleon mechanism and of the Galileon models. The former allows reconciling the presence of a scalar field with the constraints from Solar System experiments. The latter leads to inflationary models that do not need ad hoc potentials. Further generalizations lead to a tensor-scalar theory, dubbed the “Fab Four,” with only first and second order derivatives of the fields in the equations of motion that self-tune to a vanishing cosmological constant. This model needs to be confronted with experimental data in order to constrain its large parameter space. We present some results regarding a subset of this theory named “John,” which corresponds to a nonminimal derivative coupling between the scalar field and the Einstein tensor in the action. We show that this coupling gives rise to an inflationary model with very unnatural initial conditions. Thus, we include the term named “George,” namely, a nonminimal, but nonderivative, coupling between the scalar field and Ricci scalar. We find a more natural inflationary model, and, by performing a post-Newtonian analysis, we derive the set of equations that constrain the parameter space with data from experiments in the Solar System.

scholarly journals Dynamics of tachyon fields and inflation - comparison of analytical and numerical results with observation

2016 ◽  
pp. 1-8 ◽  
Author(s):  
M. Milosevic ◽  
D.D. Dimitrijevic ◽  
G.S. Djordjevic ◽  
M.D. Stojanovic
Keyword(s):  
Scalar Field ◽  
String Theory ◽  
Numerical Methods ◽  
Spectral Index ◽  
Early Universe ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
Homogeneous Universe ◽  
The Given ◽  
Good Agreement

The role tachyon fields may play in evolution of early universe is discussed in this paper. We consider the evolution of a flat and homogeneous universe governed by a tachyon scalar field with the DBI-type action and calculate the slow-roll parameters of inflation, scalar spectral index (n), and tensor-scalar ratio (r) for the given potentials. We pay special attention to the inverse power potential, first of all to V (x) ~ x?4, and compare the available results obtained by analytical and numerical methods with those obtained by observation. It is shown that the computed values of the observational parameters and the observed ones are in a good agreement for the high values of the constant X0. The possibility that influence of the radion field can extend a range of the acceptable values of the constant X0 to the string theory motivated sector of its values is briefly considered.

Reconstruction of warm Chaplygin gas inflationary models

2020 ◽  
Vol 35 (32) ◽  
pp. 2050268
Author(s):  
Abdul Jawad ◽  
Shamaila Rani ◽  
Kazuharu Bamba ◽  
Nadeem Azhar
Keyword(s):  
Spectral Index ◽  
Effective Potential ◽  
Chaplygin Gas ◽  
Index Formula ◽  
Curvature Perturbation ◽  
Warm Inflation ◽  
Scalar Spectral Index ◽  
Dissipative Coefficient ◽  
Inflationary Parameters ◽  
Friedmann Robertson Walker

By assuming the specific Chaplygin gas model, we study the reconstruction of warm inflation model with the help of tensor-to-scalar ratio [Formula: see text] and scalar spectral index [Formula: see text]. In this regard, we take flat Friedmann–Robertson–Walker (FRW) metric and discuss the general forms of dissipative coefficient [Formula: see text] as well as effective potential [Formula: see text] for two dissipative regimes i.e., the weak and strong. We use inflationary parameters such as slow-roll parameters, power spectrum of the curvature perturbation, tensor spectrum, spectral index, scalar-to-tensor ratio and Hubble parameter to find the generalized form of dissipative coefficient and effective potential. We discuss the results of dissipative coefficient and reconstructed potential in detail for the specific choice of tensor-to-scalar ratio [Formula: see text] and scalar spectral index [Formula: see text].

New constraint of an attractor GL model in braneworld context

2017 ◽  
Vol 32 (19n20) ◽  
pp. 1750119
Author(s):  
Z. Mounzi ◽  
A. Safsafi ◽  
M. Ferricha-Alami ◽  
M. Bennai
Keyword(s):  
Power Spectrum ◽  
Spectral Index ◽  
Index Formula ◽  
Brane Tension ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
Central Value ◽  
Braneworld Model ◽  
Inflationary Parameters

We are interested in studying the generalization of the first chaotic inflation model in supergravity, which was proposed by Goncharov and Linde (GL model) and was recently revisited, in the framework of the Randall–Sundrum type 2 braneworld model. This model predicts a tiny ratio [Formula: see text] and [Formula: see text]. Our scenario predicts a great tensor-to-scalar ratio [Formula: see text] of the order [Formula: see text] and the central value of the scalar spectral index [Formula: see text] for a particular choice of values of brane tension [Formula: see text] and the parameter [Formula: see text]. We have shown that this scenario reproduces successfully an attractor behavior. We have also derived all known spectrum inflationary parameters, in particular the running [Formula: see text] and the power spectrum of the curvature perturbations [Formula: see text] which are widely consistent with Planck observations.

Shaft potential inspired warm inflation

2017 ◽  
Vol 14 (06) ◽  
pp. 1750088 ◽  
Author(s):  
Abdul Jawad ◽  
Amara Ilyas ◽  
Sarfraz Ahmad
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Power Spectra ◽  
Spectral Indices ◽  
Tensor Power ◽  
Planck Data ◽  
Warm Inflation ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
Inflationary Parameters

We discuss the warm inflation in the presence of shaft potential [Formula: see text], tachyon scalar field and the generalized form of dissipative coefficient [Formula: see text]. In this respect, we investigate the inflationary parameters (slow-roll parameters, number of e-folds, scalar-tensor power spectra, spectral indices, tensor-to-scalar ratio and running of scalar spectral index) in both strong and weak dissipative regimes. It is interesting to mention that our inflationary parametric results (tensor-scalar ratio, spectral index and running of spectral) are consistent with the recent observational data such as BICEP[Formula: see text], WMAP[Formula: see text] and latest Planck data.

scholarly journals Construction of inflationary scenarios with the Gauss–Bonnet term and nonminimal coupling

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Ekaterina O. Pozdeeva ◽  
Sergey Yu. Vernov
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Effective Potential ◽  
Ricci Scalar ◽  
Nonminimal Coupling ◽  
Scalar Spectral Index ◽  
Bonnet Term ◽  
Inflationary Models ◽  
Scalar Perturbations ◽  
The Way

AbstractInflationary models with a scalar field nonminimally coupled both with the Ricci scalar and with the Gauss–Bonnet term are studied. We propose the way of generalization of inflationary scenarios with the Gauss–Bonnet term and a scalar field minimally coupled with the Ricci scalar to the corresponding scenarios with a scalar field nonminimally coupled with the Ricci scalar. Using the effective potential, we construct a set of models with the same values of the scalar spectral index $$n_s$$ n s and the amplitude of the scalar perturbations $$A_s$$ A s and different values of the tensor-to-scalar ratio r.

scholarly journals α-Attractor and reheating in a model with noncanonical scalar fields

2018 ◽  
Vol 27 (07) ◽  
pp. 1850076 ◽  
Author(s):  
Narges Rashidi ◽  
Kourosh Nozari
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Scalar Fields ◽  
The Other ◽  
Model Parameters ◽  
Model Type ◽  
Field Case ◽  
A Value ◽  
Scalar Spectral Index ◽  
Cosmological Inflation

We consider two noncanonical scalar fields [tachyon and Dirac–Born–Infeld (DBI)] with E-model type of the potential. We study cosmological inflation in these models to find possible [Formula: see text]-attractors. We show that similar to the canonical scalar field case, in both tachyon and DBI models there is a value of the scalar spectral index in small [Formula: see text] limit which is just a function of the e-folds number. However, the value of [Formula: see text] in DBI model is somewhat different from the other ones. We also compare the results with Planck2015 TT, TE, EE+lowP data. The reheating phase after inflation is studied in these models which gives some more constraints on the model parameters.

Smooth hybrid inflation on brane constrained by Planck data

2014 ◽  
Vol 29 (26) ◽  
pp. 1450146 ◽  
Author(s):  
M. Ferricha-Alami ◽  
H. Chakir ◽  
J. Inchaouh ◽  
M. Bennai
Keyword(s):  
Spectral Index ◽  
Index Formula ◽  
Type Ii ◽  
Planck Data ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
Central Value ◽  
Hybrid Inflation ◽  
Kähler Potential ◽  
Braneworld Model

It is shown that, in the supersymmetric smooth hybrid inflation model with the minimal Kähler potential, the spectral index ns is larger than 0.97 in the standard inflation. In this context, we study the smooth hybrid inflationary model in the framework of the Randall–Sundrum type-II braneworld model. We derive all known inflationary spectrum parameters which are widely consistent with Planck data for a particular choice of brane tension values λ especially for number of e-folds N = 50. We reproduce the central value of the scalar spectral index ns = 0.96 whereas the ratio r~(10-4-10-3). However, the running of the scalar spectral index [Formula: see text] is not excluded from the range given by the latest observational measurements.

scholarly journals Scalar field assisted f(R) gravity inflation

2018 ◽  
Vol 15 (08) ◽  
pp. 1850137 ◽  
Author(s):  
K. Kleidis ◽  
V. K. Oikonomou
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Field Potential ◽  
Cosmological Evolution ◽  
De Sitter ◽  
Array Data ◽  
The One ◽  
Canonical Scalar Field

In this paper, we investigate the inflationary dynamics of an [Formula: see text] gravity in the presence of a canonical scalar field. We specifically choose the cosmological evolution to be a quasi-de Sitter evolution and also the [Formula: see text] gravity is assumed to be a modified version of the [Formula: see text] gravity. We investigate which scalar field potential can produce the quasi-de Sitter evolution for the choice of the [Formula: see text] gravity we made, and also we study in detail the inflationary dynamics of the resulting theory. As we demonstrate, the spectral index is identical to the one corresponding to the ordinary [Formula: see text] gravity, while the scalar-to-tensor ratio is found to be smaller than the [Formula: see text] inflation one consequently, compatibility with both the Planck 2015 and BICEP2/Keck-Array data is achieved.

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