Singular cosmological evolution using canonical and ghost scalar fields

Nojiri, Shin’ichi; Odintsov, Sergei D.; Oikonomou, V. K.; Saridakis, Emmanuel N.

doi:10.1088/1475-7516/2015/09/044

Cited by 46 publications

(44 citation statements)

References 149 publications

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“…However, in the case of milder singularities, like the Type IV, the physical quantities do not diverge and therefore the passage of the Universe through such a singularity is smooth. However, the existence of the singularity can be responsible for a number of interesting phenomenological consequences, as was demonstrated in [6][7][8]. Particularly, as was shown in [7], the existence of a Type IV singularity in a scalar-tensor cosmological framework, generates an instability in the second Hubble slow-roll parameter [12], a fact that can indicate a possible mechanism for the graceful exit from inflation for that scalar-tensor model.…”

Section: Introductionmentioning

confidence: 88%

“…In addition, the Hubble rate and it's first derivative also remain finite, but the higher derivatives, or some higher derivative, diverge. For some phenomenological consequences of this singularity, see [6][7][8].…”

Section: Finite Time Singularities Essentials and Conventionsmentioning

confidence: 99%

“…The timelike singularities are known in cosmology as finite time singularities and where firstly extensively classified in [3]. Among these, there are crushing type singularities, like the Big Rip [4], but also milder singularities, like the Type IV singularity [3,[5][6][7][8]. In the same class of milder singularities belong the sudden singularities, firstly studied in [9,10], and further developed in [11].…”

Section: Introductionmentioning

confidence: 99%

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Singular inflationary universe fromF(R)gravity

2015

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Unlike crushing singularities, the so-called Type IV finite-time singularity offers the possibility that the Universe passes smoothly through it, without any catastrophic effects. Then the question is if the effects of a Type IV singularity can be detected in the process of cosmic evolution. In this paper we address this question in the context of F (R) gravity. As we demonstrate, the effects of a Type IV singularity appear in the Hubble flow parameters, which determine the dynamical evolution of the cosmological system. So we study various inflation models incorporating a Type IV singularity, with the singularity occurring at the end of inflation. Particularly we study a toy model and a singular version of the R 2 gravity Hubble rate. As we evince, some of the Hubble flow parameters become singular at the singularity, an effect which indicates that at that point a dynamical instability occurs. This dynamical instability eventually indicates the graceful exit from inflation. We demonstrate that the toy model has an unstable de Sitter point at the singularity, so indeed graceful exit could be triggered. In the case of the singular inflation model, graceful exit proceeds in the standard way. In addition, we investigate how the form of the F (R) gravity affects the singularity structure of the Hubble flow parameters. In the case of the singular inflation model, we found various scenarios for singular evolution, most of which are compatible with observations, and only one leads to severe instabilities. In addition, in one of these scenarios, the presence of the Type IV singularity, slightly modifies the spectral index of primordial curvature perturbations. We also compare the ordinary Starobinsky with the singular inflation model, and we point out the qualitative and quantitative differences. Finally, we study the late-time dynamics of the toy model and of the singular inflation model and we demonstrate that the unification of early and late-time acceleration can be achieved. We also show that it is possible to achieve late-time acceleration similar to the Λ-Cold Dark Matter model. PACS numbers: 04.50. Kd, 95.36.+x, 98.80.Cq,

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Section: Introductionmentioning

confidence: 88%

Section: Finite Time Singularities Essentials and Conventionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Singular inflationary universe fromF(R)gravity

2015

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“…Actually, the graceful exit procedure may be enhanced by the presence of a Type IV singularity, as was shown in [26]. For recent work on the Type IV singularities see [22][23][24][25][26], while for important earlier works on sudden singularities see [27,28], and for alternative works on the graceful exit issue, see [29]. Since the inflationary era [21] is very important for present time observations, we shall investigate how a Type IV singularity can affect the dynamics of this era, in the context of bimetric gravity.…”

Section: Introductionmentioning

confidence: 87%

“…Recall that since the singularity is a Type IV one, the parameter γ has to obey γ > 1 and also γ must not an integer in (25). Therefore, by using the above equations, when 1 < γ < 2, we find,…”

Section: Bigravity Essentialsmentioning

confidence: 96%

Singular accelerated evolution in massiveF(R)bigravity

2015

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In Eq. (1), R (g) and R (f ) represent the scalar curvatures for the Jordan frame metrics g J µν and f J µν , respectively. Also in the theory there exist two mass scales, the two Planck masses M f and M g , and we define M eff to be equal to,In addition, we also define the tensor g −1 f by using the square root of g J µρ f J ρν , so that the following holds true,The symbols e n (X)'s are defined for a general tensor X µ ν in the following way,where the trace of the tensor X (1), with respect to ϕ and ξ, we can obtain algebraic equations that relate the Ricci scalars to the auxiliary fields ϕ and ξ. The resulting algebraic equations can, in principle, be solved algebraically with respect to the auxiliary fields ϕ and ξ, and upon substituting the resulting expressions into (1) we can obtain the F (R) bigravity action which does not include the auxiliary scalars ϕ and ξ.By conformally transforming the Jordan frame metric tensors g J µν and f J µν in the following way,

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A causal viscous cosmology without singularities

Laciana

2017

Gen Relativ Gravit

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An isotropic and homogeneous cosmological model with a source of dark energy is studied. That source is simulated with a viscous relativistic fluid with minimal causal correction. In this model the restrictions on the parameters coming from the following conditions are analized: a) energy density without singularities along time, b) scale factor increasing with time, c) universe accelerated at present time, d) state equation for dark energy with "w" bounded and close to -1. It is found that those conditions are satified for the following two cases. i) When the transport coefficient (τ Π), associated to the causal correction, is negative, with the aditional restriction ζ |τ Π| > 2/3, where ζ is the relativistic bulk viscosity coefficient. The state equation is in the "phantom" energy sector. ii) For τ Π positive, in the "k-essence" sector. It is performed an exact calculation for the case where the equation of state is constant, finding that option (ii) is favored in relation to (i), because in (ii) the entropy is always increasing, while this does no happen in (i).

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Singular cosmological evolution using canonical and ghost scalar fields

Cited by 46 publications

References 149 publications

Singular inflationary universe fromF(R)gravity

Singular inflationary universe fromF(R)gravity

Singular accelerated evolution in massiveF(R)bigravity

A causal viscous cosmology without singularities

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