Palatini f(R) Gravity and Variants of k-/Constant Roll/Warm Inflation within Variation of Strong Coupling Scenario

AlHallak, M.; Alrakik, Amer; Chamoun, N.; El-Daher, Moustafa Sayem

doi:10.3390/universe8020126

Cited by 13 publications

(9 citation statements)

References 36 publications

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“…the theoretical results of different cases and limitations are compared to the joint 68 and 95% CL regions for n s , and r, obtained from Planck 2018 and lensing data alone, and their combinations with BICEP2/Keck Array (BK15) and BAO data, in addition to a forecast posterior contours of the CMB experiments (Simons Observatory, CMB-S4, and LiteBIRD)considered in [14].NI, ExP, and NS stand for Natural inflation, Exponential Potential, and New Scan, respectively. In figure (1), we reproduce most of the results of [5] and [6] regarding the cases of table (2). The exemplified results of figure (1) were largely in agreement with the observations of Planck2018 [5], [6].…”

Section: Resultssupporting

confidence: 84%

“…In figure (1), we reproduce most of the results of [5] and [6] regarding the cases of table (2). The exemplified results of figure (1) were largely in agreement with the observations of Planck2018 [5], [6]. We see, however, that the opposite occurs when Planck 2018 and lensing data alone and their combinations with BICEP2/Keck Array (BK15) and BAO data are taken into account.…”

Section: Resultssupporting

confidence: 84%

“…This section summarizes the three prominent cases examined in [5] and [6], including cosine potential with periodic/non-periodic non-minimal coupling and the exponential potential with an inverse exponential coupling to gravity. A summary of the three study cases is presented in Table (2).…”

Section: Case Study : Cosine Andxponential Potentialsmentioning

confidence: 99%

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On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

AlHallak¹

2023

Preprint

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Single field inflationary models are investigated within Palatini quadratic gravity represented by R + αR 2 along with a non-minimal coupling of the form f (φ)R between the inflaton field φ and the gravity. The treatment is performed in the Einstein frame, where the minimal coupling to gravity is recovered through conformal transformation. We consider various limits of the model with different inflationary scenarios characterized as canonical slow-roll inflation in the limit α φ2(1 + f (φ)), constant-roll kinflation for α 1, and slow-roll K-inflation forα 1 . A cosine and exponential potential are examined with the limits mentioned above and different well-motivated non-minimal couplings to gravity. We compare the theoretical results, exemplified by the tensor-to-scalar r ratio and spectral index n s , with the recent observational results of Planck 2018 & BICEP/Keck . Furthermore, we include the results of a new study forecast precision with which n s and r can be constrained by currently envisaged observations, including CMB (Simons Observatory, CMB-S4, and LiteBIRD)

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Section: Resultssupporting

confidence: 84%

Section: Resultssupporting

confidence: 84%

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On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

AlHallak¹

2023

Preprint

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“…In [78], we studied the effect of both NMC to gravity and an extended αR 2 gravity applied to an inflationry model inspired by "variation of constants" leading to an exponential potential of a certain form, and found that the joint effects of both factors allowed an accommodation with data. On the other side, we apply the same techniques in this work on the NI and see that both effects allow a sort of "focusing" of the predictions, so that increasing "α" pushes the predictions downward towards smaller r whereas increasing the NMC parameter "ξ" pushes the predictions rightward towards larger n s , and that both factors play in a disjoint way of each other, in such a way that one can meet the observational constraints, even if they were tight.…”

Section: Jcap10(2022)001mentioning

confidence: 99%

Natural Inflation with non minimal coupling to gravity in R ² gravity under the Palatini formalism

AlHallak

Chamoun

El-Daher

2022

J. Cosmol. Astropart. Phys.

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Natural Inflation with non-minimal coupling (NMC) to gravity, embodied by a Lagrangian term ξϕ 2 R, is investigated in the context of an extended gravity of the form R + αR 2. The treatment is performed in the Palatini formalism. We discuss various limits of the model “α ≫ 1” and “α ≪ 1” in light of two scenarios of inflation: a “Slow roll” and a “Constant roll” scenario. By analyzing the observational consequences of the model, our results show a significant improvement regarding compatibility between the theoretical results of this model and the observational constraints from Planck 2018 and BICEP/Keck 2018, as exemplified by the tensor-to-scalar ratio and spectral index. Furthermore, a broader range for the parameter space of natural inflation is now compatible with the confidence contours of Planck & BICEP/Keck results. The joint effects of the contributions of both the NMC to gravity and the αR 2 make a significant improvement: αR 2 gravity influences scalar-tensor ratio values, whereas NMC to gravity has a more significant impact on the spectral index values. Contributions from both terms allow more previously excluded intervals to be included being compatible now with observational data. These conclusions about the roles of NMC to gravity and, particularly, the extended gravity remain mainly valid with a periodic NMC similar in form to the natural inflation potential.

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“…Strictly speaking, we are assuming also the potential V(φ) to be negligible. This assumption can be supported in relation to the inflation theory, for which during the Planck era the inflation field ( [3,37]) is a non-interacting field (for an alternative paradigm about the power-law inflation in the f (R) gravity see [38,39]). The conditions under which the potential of the f (R) theory is negligible will be discussed later.…”

Section: Kasner-like Solutions In F (R)-gravitymentioning

confidence: 98%

Features of the primordial Universe in f(R)-gravity as viewed in the Jordan frame

Nicola¹,

Costantini²,

Montani³

2022

Class. Quantum Grav.

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We analyze some features of the primordial Universe as viewed in the Jordan frame formulation of the $f(R)$-gravity when the potential term is negligible. We start formulating the Hamiltonian picture using the 3-metric determinant as a basic variable and we outline that its conjugated momentum appears linearly only in the scalar constraint. We construct the formalism to characterize the dynamics of a generic inhomogeneous cosmological model and specialize it to describe behaviors of the Bianchi Universes, both on a classical and a quantum regime. We demonstrate that, when the potential term of the additional scalar mode is negligible near to the initial singularity, the Bianchi IX cosmology is no longer affected by the chaotic behavior, typical in the vacuum of the Einsteinian dynamics. In fact, the presence of the Kasner stability region and its attractive character are properly characterized. Finally, we investigate the canonical quantization of the Bianchi I model, using as time variable the non-minimally coupled scalar field and showing that the existence of a conserved current is outlined for the corresponding Wheeler-DeWitt (WDW) equation. The behavior of a localized wave-packet for the isotropic Universe is also evolved, demonstrating that the singularity is still present in this revised quantum dynamics.

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Palatini f(R) Gravity and Variants of k-/Constant Roll/Warm Inflation within Variation of Strong Coupling Scenario

Cited by 13 publications

References 36 publications

On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

Natural Inflation with non minimal coupling to gravity in R ² gravity under the Palatini formalism

Features of the primordial Universe in f(R)-gravity as viewed in the Jordan frame

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Palatini f(R) Gravity and Variants of k-/Constant Roll/Warm Inflation within Variation of Strong Coupling Scenario

Cited by 13 publications

References 36 publications

On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

On cosmological Inflation In Palatini $F(R,ϕ)$ Gravity

Natural Inflation with non minimal coupling to gravity in R 2 gravity under the Palatini formalism

Features of the primordial Universe in f(R)-gravity as viewed in the Jordan frame

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Natural Inflation with non minimal coupling to gravity in R ² gravity under the Palatini formalism