The null energy condition and instability

Buniy, Roman V.; Hsu, Stephen; Murray, Brian M.

doi:10.1103/physrevd.74.063518

Cited by 71 publications

(72 citation statements)

References 29 publications

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“…In the case of two-derivative field theories, there are good reasons to believe that NEC violation goes hand-in-hand with pathologies such as superluminal signal propagation, unitarity violations, and instabilities [33,34,35,36]. There are mechanisms by which the NEC can be violated in theories of physical interest.…”

Section: Discussionmentioning

confidence: 99%

“…In the classic Kaluza-Klein reduction, shape and size parameters (moduli) of the underlying theory, and it seems likely that most "well-behaved" theories should satisfy the NEC. There are some rigorous formulations of this belief, where NEC violation is shown to lead to superluminal propagation, instabilities, and violations of unitarity or causality [30,31,32,33,34,35,36]. Certainly the NEC forbids a number of solutions to Einstein's equations with strange properties: traversable wormholes [37,38], superluminal "warp drives" [39,40,41,42,43,44], time machines [45,46], universes with big rip singularities [47,48], and pathologies with gravitational thermodynamics [49,50,51,52,53] are possible with NECviolating "exotic" matter.…”

Section: Introductionmentioning

confidence: 99%

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Oxidised cosmic acceleration

Wesley

2009

J. Cosmol. Astropart. Phys.

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Abstract:We give detailed proofs of several new no-go theorems for constructing flat fourdimensional accelerating universes from warped dimensional reduction. These new theorems improve upon previous ones by weakening the energy conditions, by including time-dependent compactifications, and by treating accelerated expansion that is not precisely de Sitter. We show that de Sitter expansion violates the higher-dimensional null energy condition (NEC) if the compactification manifold M is one-dimensional, if its intrinsic Ricci scalarR vanishes everywhere, or ifR and the warp function satisfy a simple limit condition. If expansion is not de Sitter, we establish threshold equation-of-state parameters w below which accelerated expansion must be transient. Below the threshold w there are bounds on the number of e-foldings of expansion. If M is one-dimensional orR everywhere vanishing, exceeding the bound implies the NEC is violated. IfR does not vanish everywhere on M, exceeding the bound implies the strong energy condition (SEC) is violated. Observationally, the w thresholds indicate that experiments with finite resolution in w can cleanly discriminate between different models which satisfy or violate the relevant energy conditions.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oxidised cosmic acceleration

Wesley

2009

J. Cosmol. Astropart. Phys.

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“…• Ghost-condensate As summarized in [359], the violation of the NEC in theories that involve one derivative per field, L(φ I , ∂φ I ), implies the existence of either ghosts, gradient instabilities or superluminal propagation of perturbations [354,369]. In the previous paragraph, we discussed a few models which assumed such ghost fields for a finite duration.…”

Section: • Ghost Fieldsmentioning

confidence: 99%

A critical review of classical bouncing cosmologies

2015

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Given the proliferation of bouncing models in recent years, we gather and critically assess these proposals in a comprehensive review. The PLANCK data shows an unmistakably red, quasi scaleinvariant, purely adiabatic primordial power spectrum and no primary non-Gaussianities. While these observations are consistent with inflationary predictions, bouncing cosmologies aspire to provide an alternative framework to explain them. Such models face many problems, both of the purely theoretical kind, such as the necessity of violating the NEC and instabilities, and at the cosmological application level, as exemplified by the possible presence of shear. We provide a pedagogical introduction to these problems and also assess the fitness of different proposals with respect to the data. For example, many models predict a slightly blue spectrum and must be fine-tuned to generate a red spectral index; as a side effect, large non-Gaussianities often result.We highlight several promising attempts to violate the NEC without introducing dangerous instabilities at the classical and/or quantum level. If primordial gravitational waves are observed, certain bouncing cosmologies, such as the cyclic scenario, are in trouble, while others remain valid. We conclude that, while most bouncing cosmologies are far from providing an alternative to the inflationary paradigm, a handful of interesting proposals have surfaced, which warrant further research. The constraints and lessons learned as laid out in this review might guide future research.

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“…Они играют важную роль в общей теории относительности, в особенности при рассмотрении черных дыр и космологических особенностей (см. работы [1]- [7] и приведенные там ссылки).…”

Section: Introductionunclassified

“…Существуют общие теоремы, которые утверждают, что если в модели гравита-ции, взаимодействующей со скалярными полями, нарушено NEC, то такая модель нестабильна [3]- [5], [7], [12]. Однако недавно были сделаны попытки построить мо-дели, к которым эти общие теоремы не применимы.…”

Section: Introductionunclassified

Об Изотропном Энергетическом Условии И Космологии

Арефьева¹,

Aref’eva²,

Волович³

2008

ТМФ

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Полевые теории, которые нарушают изотропное энергетическое условие, представляют интерес как для решения проблемы космологической сингуляр-ности, так и для моделей космологической темной энергии с параметром урав-нения состояния w < −1. Рассмотрены две недавно предложенные модели, которые нарушают это условие. Модель фантомного конденсата требует выс-ших производных, что приводит к появлению массивного фантома и не ограни-ченной снизу энергии. Дается оценка скорости распада частиц и обсуждаются возможные ограничения на массы, необходимые для того, чтобы обеспечить стабильность частиц в модели фантомного конденсата. Нелокальная струнная модель, которая появляется в кубической полевой струнной теории и прояв-ляет фантомное поведение, также приводит к не ограниченной снизу энергии. В этом случае спектр энергии непрерывен и частицеподобные возбуждения от-сутствуют. Эта модель допускает естественное ультрафиолетовое пополнение, так как она выводится из теории суперструны.

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The null energy condition and instability

Cited by 71 publications

References 29 publications

Oxidised cosmic acceleration

Oxidised cosmic acceleration

A critical review of classical bouncing cosmologies

Об Изотропном Энергетическом Условии И Космологии

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