Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem

Akama, Shingo; Hirano, Shin‐ichi; Kobayashi, Tsutomu

doi:10.1103/physrevd.101.043529

Cited by 18 publications

(11 citation statements)

References 86 publications

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“…The "no-go" theorem proved in [56,57] indicates that pathological instabilities of perturbations appear in either the NEC-violating period or sooner or later in spatial flat nonsingular cosmology constructed by Horndeski theory [58][59][60], see also [61][62][63][64][65][66][67][68][69]. It is then demonstrated explicitly with the EFT method [70][71][72][73][74] that fully stable NEC-violating nonsingular cosmological models can be constructed in "beyond Horndeski" theories [75,76], see [77][78][79][80][81][82][83][84][85][86][87][88][89][90] for later developments. Notably, the physics represented by higher derivative "beyond Horndeski" operators plays an essential role in realizing fully stable NEC-violating nonsingular cosmology.…”

Section: Jhep10(2022)140mentioning

confidence: 97%

Perturbative unitarity and NEC violation in genesis cosmology

Cai

Xu²,

Zhou³

2022

J. High Energ. Phys.

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Explorations of the violation of null energy condition (NEC) in cosmology could enrich our understanding of the very early universe and the related gravity theories. Although a fully stable NEC violation can be realized in the “beyond Horndeski” theory, it remains an open question whether a violation of the NEC is allowed by some fundamental properties of UV-complete theories or the consistency requirements of effective field theory (EFT). We investigate the tree-level perturbative unitarity for stable NEC violations in the contexts of both Galileon and “beyond Horndeski” genesis cosmology, in which the universe is asymptotically Minkowskian in the past. We find that the constraints of perturbative unitarity imply that we may need some unknown new physics below the cut-off scale of the EFT other than that represented by the “beyond Horndeski” operators.

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Section: Jhep10(2022)140mentioning

confidence: 97%

Perturbative unitarity and NEC violation in genesis cosmology

Cai

Xu²,

Zhou³

2022

J. High Energ. Phys.

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“…[74,75], authors discussed that in matter bounce scenario driven by Horndeski theory, one could not get small r while keeping f nl small enough to be within the current constraints (a.k.a. no-go theorem), while it is also interesting to consider such constraints for other early universe scenarios/models (examples has been given in [76]). We will address the above discussion in future works.…”

Section: Resultsmentioning

confidence: 99%

Confronting inflation models with the coming observations on primordial gravitational waves

Qiu

Katsuragawa

2020

Eur. Phys. J. C

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The recent observations from CMB have imposed a very stringent upper-limit on the tensor/scalar ratio r of inflation models, $$r < 0.064$$ r < 0.064 , which indicates that the primordial gravitational waves (PGW), even though possible to be detected, should have a power spectrum of a tiny amplitude. However, current experiments on PGW is ambitious to detect such a signal by improving the accuracy to an even higher level. Whatever their results are, it will give us much information about the early Universe, not only from the astrophysical side but also from the theoretical side, such as model building for the early Universe. In this paper, we are interested in analyzing what kind of inflation models can be favored by future observations, starting with a kind of general action offered by the effective field theory (EFT) approach. We show a general form of r that can be reduced to various models, and more importantly, we show how the accuracy of future observations can put constraints on model parameters by plotting the contours in their parameter spaces.

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“…For example, in [90], it is found that the new physics at the bouncing phase has negligible contribution to the power spectrum. Consequently, in many studies of non-singular cosmology [96][97][98][99][100][101][102][103], the signals from the bouncing phase are small, the main phenomenological contribution comes from the contraction phase, so it's difficult to probe the new physics in bouncing phase 1 . Specifically, in previous literature addressing the parity-violation effect in bouncing cosmology [10], the bouncing phase is directly replaced by a simple junction condition so there is only a contraction and an expansion in their scenario.…”

Section: Introductionmentioning

confidence: 99%

Parity-violation in bouncing cosmology

Zhu¹,

Cai²

2023

Preprint

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We investigate the possibility of the enhancement of parity-violation signal in bouncing cosmology. Specifically, we are interested in deciding which phase should generate the most significant parity-violation signals. We find that the dominant contribution comes from the bouncing phase, while the contraction phase has a smaller contribution. Therefore, bouncing cosmology can enhance the parity-violation signals during the bouncing phase. Moreover, since the bouncing phase has the highest energy scale in bouncing cosmology, we can also probe new physics at this scale by studying the parity-violation effect.

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Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem

Cited by 18 publications

References 86 publications

Perturbative unitarity and NEC violation in genesis cosmology

Perturbative unitarity and NEC violation in genesis cosmology

Confronting inflation models with the coming observations on primordial gravitational waves

Parity-violation in bouncing cosmology

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