Is limiting curvature mimetic gravity an effective polymer quantum gravity?

Bodendorfer, Norbert; Mele, Fabio M.; Münch, Johannes

doi:10.1088/1361-6382/aae74b

Cited by 22 publications

(19 citation statements)

References 46 publications

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“…• The claim that effective equations "arise from a (first order) covariant action" is incorrect because the proposed action fails in vacuum models. Similarly, more advanced recent versions which include a scalar field [85,86] fail to describe anisotropic or inhomogeneous modes in congruence with loop quantum cosmology [87,88,89,90].…”

Section: What's Left?mentioning

confidence: 99%

Critical Evaluation of Common Claims in Loop Quantum Cosmology

Bojowald

2020

Universe

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A large number of models have been analyzed in loop quantum cosmology, using mainly minisuperspace constructions and perturbations. At the same time, general physics principles from effective field theory and covariance have often been ignored. A consistent introduction of these ingredients requires substantial modifications of existing scenarios. As a consequence, none of the broader claims made mainly by the Ashtekar school -such as the genericness of bounces with astonishingly semiclassical dynamics, robustness with respect to quantization ambiguities, the realization of covariance, and the relevance of certain technical results for potential observations -hold up to scrutiny. Several useful lessons for a sustainable version of quantum cosmology can be drawn from this outcome. * e-mail address: bojowald@gravity.psu.edu 1 All quotations from [1] given in this paper refer to the second preprint version.

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Section: What's Left?mentioning

confidence: 99%

Critical Evaluation of Common Claims in Loop Quantum Cosmology

Bojowald

2020

Universe

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“…An example is given by mimetic gravity and its extension [110], which can be reformulated in the DHOST framework [111]. This theory and its extensions have been used to provide effective regular cosmological and black hole models [112][113][114][115], as well as covariant action for effective quantum cosmology and quantum black holes models inspired by loop quantum gravity [116][117][118][119][120].…”

Section: Introductionmentioning

confidence: 99%

Hairy black holes in DHOST theories: exploring disformal transformation as a solution generating method

Achour

Liu

Mukohyama

2020

J. Cosmol. Astropart. Phys.

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Solutions-generating methods based on field redefinitions, such as conformal mapping, play an important role in investigating exact solutions in modified gravity. In this work, we explore the possibility to use disformal field redefinitions to investigate new regions of the solution space of DHOST theories, and present new hairy black holes solutions beyond the stealth sector. The crucial ingredient is to find suitable seed solutions to generate new exact ones for DHOST theories. We first consider a seed solution of the Einstein-Scalar system describing a naked singularity. Under suitable assumptions, we derive a no-go result showing that no black hole solution can be constructed from such a seed GR solution. Then, taking into account the stability of each three degeneracy classes of quadratic DHOST theories under a general disformal mapping, we consider two kinds of known black hole solutions as seed configurations: the Schwarzschild stealth solution and the non-stealth Reissner-Nordstrom like solution. Restricting our considerations to invertible disformal transformations, we show that building new hairy black hole solutions from the stealth solution associated to a constant kinetic term is also quite constrained. We obtain new solutions which either are stealth or describe asymptotically locally flat black holes with a deficit solid angle. However, starting from the non-stealth seed solution associated to a non constant kinetic term, we show that a disformal transformation can introduce rather general modifications of the exterior geometry. Finally, we consider the construction of minimally modified hairy black hole solutions using a small disformal transformation. Further applications of this solution generating method should allow to provide new hairy rotating black hole solutions beyond the stealth sector, as well as minimally modified GR solutions useful for phenomenological investigations of compact objects beyond GR.

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“…As a first explicit example, it is possible to compute the evolution of the time-dependent Kasner exponents in the limiting curvature mimetic gravity theory [6], which satisfies Conditions (i) and (ii). (Note that while limiting curvature mimetic gravity exactly reproduces the LQC effective dynamics for a spatially flat FLRW model [40,41], the dynamics are different for the Bianchi I space-time [42].) For limiting curvature mimetic gravity, the modified Friedmann equation obeyed by the mean scale factor is…”

Section: Application To Modified Gravity Theories With a Bouncementioning

confidence: 90%

A generalized Kasner transition for bouncing Bianchi I models in modified gravity theories

Cesare

Wilson-Ewing

2019

J. Cosmol. Astropart. Phys.

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We derive transition rules for Kasner exponents in bouncing Bianchi I models with generic perfect fluid matter fields for a broad class of modified gravity theories where cosmological singularities are resolved and replaced by a non-singular bounce. This is a generalization of results obtained previously in limiting curvature mimetic gravity and loop quantum cosmology. A geometric interpretation is provided for the transition rule as a linear map in the Kasner plane. We show that the general evolution of anisotropies in a Bianchi I universe-including during the bounce phase-is equivalent to the motion of a point particle on a sphere, where the sphere is the one-point compactification of the Kasner plane. In addition, we study the evolution of anisotropies in a large family of bouncing Bianchi I space-times. We also present a novel explicit solution to the Einstein equations for a Bianchi I universe with ekpyrotic matter with a constant equation of state ω = 3. *

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Is limiting curvature mimetic gravity an effective polymer quantum gravity?

Cited by 22 publications

References 46 publications

Critical Evaluation of Common Claims in Loop Quantum Cosmology

Critical Evaluation of Common Claims in Loop Quantum Cosmology

Hairy black holes in DHOST theories: exploring disformal transformation as a solution generating method

A generalized Kasner transition for bouncing Bianchi I models in modified gravity theories

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