On (in)stabilities of perturbations in mimetic models with higher derivatives

Zheng, Yunlong; Shen, Liuyuan; Mou, Yicen; Li, Mingzhe

doi:10.1088/1475-7516/2017/08/040

Cited by 63 publications

(107 citation statements)

References 59 publications

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“…Perturbations in mimetic gravity have been studied in Refs. [9,53,57,58,81,86,87] (for higher-derivative extensions see [11,59,88,89]). Similar comparisons have been carried out between LQC and the mimetic gravity theory reproducing its background evolution [81].…”

Section: Resultsmentioning

confidence: 99%

Limiting curvature mimetic gravity for group field theory condensates

Cesare

2019

Phys. Rev. D

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Nonsingular bouncing cosmologies are realized in limiting curvature mimetic gravity by means of a multivalued potential f ( φ) depending on the d'Alembertian of a scalar field φ. We determine the functional form of such a potential so as to exactly reproduce the cosmological background dynamics obtained in the group field theory approach to quantum gravity. The original proposal made by Chamseddine and Mukhanov [JCAP 1703[JCAP , no. 03, 009 (2017], which was shown to lead to a background dynamics reproducing the effective dynamics of loop quantum cosmology, is here recovered as a particular case for some specific choices of the parameters of our model. We also clarify some issues related to the multi-valuedness of the function f , showing in particular that its functional form can be unambiguously reconstructed by imposing appropriate matching conditions at the branching points.

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Section: Resultsmentioning

confidence: 99%

Limiting curvature mimetic gravity for group field theory condensates

Cesare

2019

Phys. Rev. D

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“…We conclude mentioning theoretical issues pertaining the instability of the theory. It has recently been argued that mimetic gravity and its higher-order extensions suffer from gradient and ghost instability issues, which undermine the theoretical consistency of the theory [106][107][108][109][110][111][112][113][114][115] 10 . Although in this work we have imposed specific conditions on the parameters to avoid ghost instabilities, we notice that more generally there exist paths to curing these instabilities, for instance by considering direct couplings between higher derivatives of the mimetic field and curvature [110-112, 114, 115].…”

Section: Discussionmentioning

confidence: 99%

Alive and well: mimetic gravity and a higher-order extension in light of GW170817

Casalino

Rinaldi

Sebastiani

et al. 2018

Class. Quantum Grav.

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The near-simultaneous multi-messenger detection of the gravitational wave (GW) event GW170817 and its optical counterpart, the short γ-ray burst GRB170817A, implies that deviations of the GW speed from the speed of light are restricted to being of O(10 −15 ). In this note, we study the implications of this bound for mimetic gravity and confirm that in the original setting of the theory, GWs propagate at the speed of light, hence ensuring agreement with the recent multi-messenger detection. A higher-order extension of the original mimetic theory, appearing in the low-energy limit of projectable Hořava-Lifshitz gravity, is then considered. Performing a Bayesian statistical analysis where we compare the predictions of the higher-order mimetic model for the speed of GWs against the observational bound from GW170817/GRB170817A, we derive constraints on the three free parameters of the theory. Imposing the absence of both ghost instabilities and superluminal propagation of scalar and tensor perturbations, we find very stringent 95% confidence level upper limits of ∼ 7 × 10 −15 and ∼ 4 × 10 −15 on the coupling strengths of Lagrangian terms of the form ∇ µ ∇ ν φ∇µ∇ν φ and ( φ) 2 respectively, with φ the mimetic field. We discuss implications of the obtained bounds for mimetic theories. This work presents the first ever robust comparison of a mimetic theory to observational data.

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“…The mimetic gravity with the couple ( φ)R has been proposed in ref. [54]. We will back to the relevant issues.…”

Section: Jhep09(2017)027 4 Discussionmentioning

confidence: 99%

A covariant Lagrangian for stable nonsingular bounce

Cai

Piao

2017

J. High Energ. Phys.

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Abstract:The nonsingular bounce models usually suffer from the ghost or gradient instabilities, as has been proved recently. In this paper, we propose a covariant effective theory for stable nonsingular bounce, which has the quadratic order of the second order derivative of the field φ but the background set only by P (φ, X). With it, we explicitly construct a fully stable nonsingular bounce model for the ekpyrotic scenario.

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On (in)stabilities of perturbations in mimetic models with higher derivatives

Cited by 63 publications

References 59 publications

Limiting curvature mimetic gravity for group field theory condensates

Limiting curvature mimetic gravity for group field theory condensates

Alive and well: mimetic gravity and a higher-order extension in light of GW170817

A covariant Lagrangian for stable nonsingular bounce

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