Nearly scale-invariant spectrum of adiabatic fluctuations may be from a very slowly expanding phase of the Universe

Piao, Yun-Song; Zhou, Enbo

doi:10.1103/physrevd.68.083515

Cited by 135 publications

(100 citation statements)

References 23 publications

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“…[An analogous statement holds true in the "phantom inflation" model [36] [37].] That is, expressed in terms of the equation-of-state parameter w, the w < −1 phase must be succeeded by a w > −1 era, corresponding to the inflaton.…”

Section: The Global Formulation Of String Gas Spacetimesmentioning

confidence: 99%

“…Notice too that if the inflationary era is governed by a dynamical inflaton [as opposed to a pure cosmological constant] then it follows that it must be possible for these cosmologies to make the transition from w < −1 to w > −1, where w is the equationof-state parameter. [This question was first discussed in the context of the "phantom inflation" model [36] [37].] The ability of a cosmological model to "cross the phantom divide" in this way can be a very subtle matter, as has been emphasised recently in the astrophysics literature [38] [44].…”

Section: String Gases Topology and The Null Energy Conditionmentioning

confidence: 99%

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The phantom divide in string gas cosmology

McInnes

2005

Nuclear Physics B

102

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One of the main virtues of string gas cosmology is that it resolves cosmological singularities. Since the Universe can be approximated by a locally asymptotically de Sitter spacetime by the end of the inflationary era, a singularity theorem implies that these cosmologies effectively violate the Null Energy Condition [not just the Strong Energy Condition]. We stress that this is an extremely robust result, which does not depend on assuming that the spatial sections remain precisely flat in the early Universe. This means, however, that it must be possible for string cosmologies to cross the recently much-discussed phantom divide [from w < −1 to w > −1, where w is the equation-ofstate parameter]. This naturally raises the question as to whether the phantom divide can be crossed again, to account for recent observations suggesting that w < −1 at the present time. We argue that non-perturbative string effects rule out this possibility, even if the NEC violation in question is only "effective".

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Section: The Global Formulation Of String Gas Spacetimesmentioning

confidence: 99%

Section: String Gases Topology and The Null Energy Conditionmentioning

confidence: 99%

The phantom divide in string gas cosmology

McInnes

2005

Nuclear Physics B

102

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“…However, the inflation still suffers from the cosmological singularity problem [1,2], unless it was preceded by a bounce [3][4][5][6][7] or a Genesis phase [8][9][10]. It is exciting to study classical nonsingular cosmology, such as bounce universe models [11,12], Genesis models [13][14][15], slow expansion models [16][17][18][19], since we might get classical nonsingular cosmology without begging the details of the unknown UV-complete gravity theory.…”

Section: Introductionmentioning

confidence: 99%

The Effective Field Theory of nonsingular cosmology

Cai

Wan

et al. 2017

J. High Energ. Phys.

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136

150

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In this paper, we explore the nonsingular cosmology within the framework of the Effective Field Theory (EFT) of cosmological perturbations. Due to the recently proved no-go theorem, any nonsingular cosmological models based on the cubic Galileon suffer from pathologies. We show how the EFT could help us clarify the origin of the no-go theorem, and offer us solutions to break the no-go. Particularly, we point out that the gradient instability can be removed by using some spatial derivative operators in EFT. Based on the EFT description, we obtain a realistic healthy nonsingular cosmological model, and show the perturbation spectrum can be consistent with the observations.

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“…There is an alternative to inflation, in which the primordial universe is slowly expanding, i.e. genesis scenario [20], [21], [22], also earlier [23], see [24] for a review. In this scenario, n T = 2, thus its tensor amplitude is exponentially low at large scale, which is negligible.…”

mentioning

confidence: 99%

Preinflationary genesis with CMB B-mode polarization

Liu

Li²,

Piao³

2014

Phys. Rev. D

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Recent B-mode polarization observation seems to imply the tensor tilt n T 1 at large angular scale, if the primordial signal is dominated. We show that for a primordial universe, which is in a slowly expanding genesis phase before the slow-roll inflation, the primordial tensor spectrum will get a large-scale cutoff, i.e. n T 1 at large scales while n T ≃ 0 at small scale. We find that this inflationary scenario not only may be consistent with the observation, but also predicts a large-scale anomaly in BB power spectrum, i.e. due to the large suppression of tensor perturbation amplitude we will hardly see the reionization bump at low-l, which may be falsified by the Planck polarization data.

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Nearly scale-invariant spectrum of adiabatic fluctuations may be from a very slowly expanding phase of the Universe

Cited by 135 publications

References 23 publications

The phantom divide in string gas cosmology

The phantom divide in string gas cosmology

The Effective Field Theory of nonsingular cosmology

Preinflationary genesis with CMB B-mode polarization

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