Power-law <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e263" altimg="si197.svg"><mml:mrow><mml:mi>f</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mi>R</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> gravity corrected canonical scalar field inflation

Oikonomou, V. K.

doi:10.1016/j.aop.2021.168576

Cited by 22 publications

(11 citation statements)

References 50 publications

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“…This approach is much simpler and offers insights toward understanding the inflationary era. To our opinion a synergistic approach that combines scalars and higher order curvature terms, is the most complete approach from many aspects, and there are many examples of this sort in the literature [23][24][25][26][27][28][29][30][31][32][33]. But as we said, studies of theories containing either scalar or only higher order curvature terms offer a simple path toward understanding the fundamental physics and problems of inflation.…”

Section: Introductionmentioning

confidence: 93%

Pre-Inflationary Bounce Effects on Primordial Gravitational Waves of $f(R)$ Gravity

Odintsov,

Oikonomou

2021

Preprint

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In this work we shall study a possible pre-inflationary scenario for our Universe and how this might be realized by f (R) gravity. Specifically, we shall introduce a scenario in which the Universe in the pre-inflationary era contracts until it reaches a minimum magnitude, and subsequently expands, slowly entering a slow-roll quasi-de Sitter inflationary era. This pre-inflationary bounce avoids the cosmic singularity, and for the eras before and after the quasi-de Sitter inflationary stage, approximately satisfies the string theory motivated scale factor duality a(t) = a −1 (−t). We investigate which approximate forms of f (R) can realize such a non-singular pre-inflationary scenario, the quasi-de Sitter patch of which is described by an R 2 gravity, thus the exit from inflation is guaranteed. Furthermore, since in string theory pre-Big Bang scenarios lead to an overall amplification of the gravitational wave energy spectrum, we examine in detail this perspective for the f (R) gravity generating this pre-inflationary non-singular bounce. As we show, in the f (R) gravity case, the energy spectrum of the primordial gravitational waves background is also amplified, however the drawback is that the amplification is too small to be detected by future high frequency interferometers. Thus we conclude that, as in the case of single scalar field theories, f (R) gravity cannot produce detectable stochastic gravitational waves and a synergistic theory of scalars and higher order curvature terms might be needed.

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Section: Introductionmentioning

confidence: 93%

Pre-Inflationary Bounce Effects on Primordial Gravitational Waves of $f(R)$ Gravity

Odintsov,

Oikonomou

2021

Preprint

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“…This perspective is exciting and we surely hope that this might be the case in the future. Such a result would indicate that single scalar field inflation might be assisted, not solely by curvature terms [88], but also by more exotic terms, like the Chern-Simons terms. In the case of detection of signals, cosmologists are confronted with a demanding challenge: the models that they use thereafter must provide a unified description of dark energy and inflation, with a smooth transition in between them, passing through the radiation and matter domination eras, a successful late and inflationary phenomenology, and the model must also produce the right amount of gravitational radiation in order to comply with the future detected signals.…”

Section: Future Perspectives and Concluding Remarksmentioning

confidence: 99%

Quantitative Predictions for $f(R)$ Gravity Primordial Gravitational Waves

Odintsov¹,

Oikonomou²,

Fronimos³

2021

Preprint

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In this work we shall develop a quantitative approach for extracting predictions on the primordial gravitational waves energy spectrum for f (R) gravity. We shall consider two distinct models which yield different phenomenology, one pure f (R) gravity model and one Chern-Simons corrected potential-less k-essence f (R) gravity model in the presence of radiation and non-relativistic perfect matter fluids. The two f (R) gravity models were carefully chosen in order for them to describe in a unified way inflation and the dark energy era, in both cases viable and compatible with the latest Planck data. Also both models mimic the Λ-Cold-Dark-Matter model and specifically the pure f (R) model only at late times, but the Chern-Simons k-essence model during the whole evolution of the model up to the radiation domination era. In addition they guarantee a smooth transition from the inflationary era to the radiation, matter domination and subsequently to the dark energy era. Using a WKB approach introduced in the relevant literature by Nishizawa, we derive formulas depending on the redshift that yield the modified gravity effect, quantified by a multiplicative factor, a "damping" in front of the General Relativistic waveform. In order to calculate the effect of the modified gravity, which is the "damping" factor, we solve numerically the Friedmann equations using appropriate initial conditions and by introducing specific statefinder quantities. As we show, the pure f (R) gravity gravitational wave energy spectrum is slightly enhanced, but it remains well below the sensitivity curves of future gravitational waves experiments. In contrast, the Chern-Simons k-essence f (R) gravity model gravitational wave energy spectrum is significantly enhanced and two signals are predicted which can be verified by future gravitational wave experiments. We discuss in detail our findings and the future perspective of modified gravity theories in view of the upcoming second and third generation experiments on primordial gravitational waves.

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“…Obviously, this modification to gravity is not limited to the current epoch of Universe evolution, and it can be used to study different cosmological aspects [13][14][15][16]. Cosmological inflation within f (R) gravity has been studied extensively [17][18][19][20][21][22][23][24][25]. Finally, There are several formulations of f (R) theories known under the name of metric formalism, Palatini formalism and metric-affine formalism, the last one being the most general.…”

Section: Introductionmentioning

confidence: 99%

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

Alhallak¹,

Aldaher²

2022

Preprint

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Natural Inflation with non-minimal coupling NMC to gravity (ξφ 2 ) 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 limitations of the model "α 1 and α 1" in light of two scenarios of inflation: a "Slow roll" and a "Constant roll".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 experimental ones from Planck 2018, as exemplified by the tensor-to-scalar ratio and spectral index. Furthermore, a broader range of parameter space for natural inflation is now compatible with the confidence contours of Planck results. The notable effect of both NMC and αR 2 's contributions makes it a significant improvement. αR 2 gravity influences scalar-tensor ratio values. In contrast, NMC has a more significant impact on the spectral index values. Contributions to this area allow more excluded intervals to be included and are compatible with observational data.

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Power-law f(R) gravity corrected canonical scalar field inflation

Cited by 22 publications

References 50 publications

Pre-Inflationary Bounce Effects on Primordial Gravitational Waves of $f(R)$ Gravity

Pre-Inflationary Bounce Effects on Primordial Gravitational Waves of $f(R)$ Gravity

Quantitative Predictions for $f(R)$ Gravity Primordial Gravitational Waves

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

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