Entropy production in affine inflation

Azri, Hemza; Nasri, Salah

doi:10.1103/physrevd.101.064073

Cited by 16 publications

(29 citation statements)

References 27 publications

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“…In a previous work, multiple scalar fields coupled to gravity through spacetime connection solely is thoroughly studied in the case of nonminimal coupling [16]. A remarkable feature drawn from this study is that both nonminimally and minimally coupled scalar fields are accommodated by a unique spacetime metric unlike the familiar theories in which the transformation to minimal couplings (Einstein frame) necessitates a second metric obtained from the original one (Jordan frame) by Weyl transformations.…”

Section: Introductory Remarks and Motivationsmentioning

confidence: 91%

“…. , N , and N being the number of fields, are coupled to gravity through the metric-free invariant action [16]…”

Section: A Nonminimal Couplings and Nonadiabatic Perturbationsmentioning

confidence: 99%

“…where Γ a cb are the components of the field space connection, i.e, the Christoffel symbol of the metric (16).…”

Section: B Minimal Couplings and Covariant Formalismmentioning

confidence: 99%

“…Although this equation, which is derived via the covariant formalism, takes a standard form as in the case of metric gravity, there is a crucial difference, however. The origin of the differences comes from the manifold's metric (16).…”

Section: B Minimal Couplings and Covariant Formalismmentioning

confidence: 99%

“…This alleviate the famous frame-issue since most of the important cosmological parameters such as the Hubble parameter, number of e-foldings, and the gauge invariant curvature perturbation, which are highly related to the proposed metric, are not altered by the transition to minimal coupling if no conformal transformation is applied. In this respect, one of the physical consequences of this feature is that the notion of adiabaticity (of the perturbations) is frame-independent [16].…”

Section: Introductory Remarks and Motivationsmentioning

confidence: 99%

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Isocurvature modes and non-Gaussianity in affine inflation

Azri,

Bamwidhi,

Nasri

2021

Preprint

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Section: Introductory Remarks and Motivationsmentioning

confidence: 91%

“…. , N , and N being the number of fields, are coupled to gravity through the metric-free invariant action [16]…”

Section: A Nonminimal Couplings and Nonadiabatic Perturbationsmentioning

confidence: 99%

“…where Γ a cb are the components of the field space connection, i.e, the Christoffel symbol of the metric (16).…”

Section: B Minimal Couplings and Covariant Formalismmentioning

confidence: 99%

Section: B Minimal Couplings and Covariant Formalismmentioning

confidence: 99%

Section: Introductory Remarks and Motivationsmentioning

confidence: 99%

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Isocurvature modes and non-Gaussianity in affine inflation

Azri,

Bamwidhi,

Nasri

2021

Preprint

Self Cite

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Cosmological perturbations in Palatini formalism

Kubota

Oda

Shimada

et al. 2021

J. Cosmol. Astropart. Phys.

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We investigate cosmological perturbations of scalar-tensor theories in Palatini formalism. First we introduce an action where the Ricci scalar is conformally coupled to a function of a scalar field and its kinetic term and there is also a k-essence term consisting of the scalar and its kinetic term. This action has three frames that are equivalent to one another: the original Jordan frame, the Einstein frame where the metric is redefined, and the Riemann frame where the connection is redefined. For the first time in the literature, we calculate the quadratic action and the sound speed of scalar and tensor perturbations in three different frames and show explicitly that they coincide. Furthermore, we show that for such action the sound speed of gravitational waves is unity. Thus, this model serves as dark energy as well as an inflaton even though the presence of the dependence of the kinetic term of a scalar field in the non-minimal coupling, different from the case in metric formalism. We then proceed to construct the L3 action called Galileon terms in Palatini formalism and compute its perturbations. We found that there are essentially 10 different (inequivalent) definitions in Palatini formalism for a given Galileon term in metric formalism. We also see that, in general, the L3 terms have a ghost due to Ostrogradsky instability and the sound speed of gravitational waves could potentially deviate from unity, in sharp contrast with the case of metric formalism. Interestingly, once we eliminate such a ghost, the sound speed of gravitational waves also becomes unity. Thus, the ghost-free L3 terms in Palatini formalism can still serve as dark energy as well as an inflaton, like the case in metric formalism.

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