Initial conditions for imperfect dark matter

Ramazanov, Sabir

doi:10.1088/1475-7516/2015/12/007

Cited by 36 publications

(34 citation statements)

References 40 publications

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“…In fact, the constant γ is implied to follow the renormalization group flow starting from the values of the order of the Planck mass squared. Apart from the obscure quantum gravity issues, the time dependence of γ appears to be necessary for the production of the Dark Matter with the correct initial conditions [39,84].…”

Section: Jhep06(2016)020mentioning

confidence: 99%

Living with ghosts in Hořava-Lifshitz gravity

Ramazanov

Arroja

Celoria

et al. 2016

J. High Energ. Phys.

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Abstract:We consider the branch of the projectable Hořava-Lifshitz model which exhibits ghost instabilities in the low energy limit. It turns out that, due to the Lorentz violating structure of the model and to the presence of a finite strong coupling scale, the vacuum decay rate into photons is tiny in a wide range of phenomenologically acceptable parameters. The strong coupling scale, understood as a cutoff on ghosts' spatial momenta, can be raised up to Λ ∼ 10 TeV. At lower momenta, the projectable Hořava-Lifshitz gravity is equivalent to General Relativity supplemented by a fluid with a small positive sound speed squared (10 −42 ) c 2 s 10 −20 , that could be a promising candidate for the Dark Matter. Despite these advantages, the unavoidable presence of the strong coupling obscures the implementation of the original Hořava's proposal on quantum gravity. Apart from the Hořava-Lifshitz model, conclusions of the present work hold also for the mimetic matter scenario, where the analogue of the projectability condition is achieved by a non-invertible conformal transformation of the metric.

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Section: Jhep06(2016)020mentioning

confidence: 99%

Living with ghosts in Hořava-Lifshitz gravity

Ramazanov

Arroja

Celoria

et al. 2016

J. High Energ. Phys.

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“…As such, there arises the well-known problem of defining quantum fluctuations to φ from which the large scale structures of the universe can originate [22,23,26,27,29]. Also, for the universe constituted by the dust-like mimetic matter, it is not possible to suppress the over-abundance of small scale structures [23,27,28]. A possible way to ameliorate these issues is by the including higher derivative (HD) terms for φ in the mimetic action.…”

Section: Higher Derivative Extension and Bounds On Mmt Coupling Strengthmentioning

confidence: 99%

“…In particular, the CM Lagrangian extended by a potential V (φ) leads to the scenarios of a cosmologically evolving fluid -the so-called 'mimetic fluid' -which characterizes dust, albeit with a nonvanishing pressure 1 [22]. As such, no propagating scalar perturbation mode is there to suppress the growth of structures at smaller (sub-galactic) scales [26,27]. Nor it is possible to define the quantum fluctuations to the (non-dynamical) field φ, so that the latter can provide the seeds of the observed large scale structure of the universe [22,23].…”

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confidence: 99%

“…(✷φ) 2 , which lead(s) to a non-vanishing sound speed c s of the mimetic matter perturbations, keeping the background solution unaffected qualitatively 2 [22,23,29]. However, the HD terms in general make the theory susceptible to Ostrogradsky ghost or(and) gradient instabilities [26,27,[64][65][66][67], possible wayouts of which point to more complicated extensions of the CM model. For instance, one may require to incorporate explicit HD couplings with the Ricci curvature scalar R [66-69], or resort to degenerate higher-order scalar-tensor (DHOST) Lagrangians [70,71].Noteworthy mimetic extensions from various other considerations include the mimetic f (R) gravity and its unimodular, non-local and several more variants [15,[36][37][38][39][40][41][42][72][73][74][75], mimetic Horndeski theory [76,77], mimetic Born-Infeld theory [78,79], mimetic brane-world gravity [80][81][82], mimetic massive gravity [83][84][85][86], and so on [87][88][89][90][91].…”

mentioning

confidence: 99%

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Cosmological dark sector from a mimetic–metric–torsion perspective

Chothe

Dutta

Sur

2019

Int. J. Mod. Phys. D

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We generalize the basic theory of mimetic gravity by extending its purview to the general metriccompatible geometries that admit torsion, in addition to curvature. This essentially implies reinstating the mimetic principle of isolating the conformal degree of freedom of gravity in presence of torsion, by parametrizing both the physical metric and torsion in terms of the scalar 'mimetic' field and the metric and torsion of a fiducial space. We assert the requisite torsion parametrization from an inspection of the fiducial space Cartan transformation which, together with the conformal transformation of the fiducial metric, preserve the physical metric and torsion. In formulating the scalar-tensor equivalent Lagrangian, we consider an explicit contact coupling of the mimetic field with torsion, so that the former can manifest itself geometrically as the source of a torsion mode, and most importantly, give rise to a viable 'dark universe' picture from a mimicry of an evolving dust-like cosmological fluid with a non-zero pressure. A further consideration of higher derivatives of the mimetic field in the Lagrangian leads to physical bounds on the mimetic-torsion coupling strength, which we determine explicitly. * transformation of g µν , but also implicates that φ is left non-dynamical by the condition for the invertibility of g µν , viz. −κ 2 g µν ∂ µ φ∂ ν φ = 1 . This condition could be implemented in the theory as a constraint, using a Lagrange multiplier λ in an equivalent mimetic action. A further equivalence of the latter with the singular Brans-Dicke (BD) action (in which the BD parameter w = − 3 2 ) eventually shows that mimetic gravity is indeed a ratification of GR being raised to the status of a scalar-tensor equivalent MG theory [21][22][23][24]29].Detailed studies have revealed many attractive features of the basic mimetic model of Chemseddine and Mukhanov (henceforth, the CM model [21]) and its various extensions, from the perspectives of both cosmology and astrophysics . In particular, the CM Lagrangian extended by a potential V (φ) leads to the scenarios of a cosmologically evolving fluid -the so-called 'mimetic fluid' -which characterizes dust, albeit with a nonvanishing pressure 1 [22]. As such, no propagating scalar perturbation mode is there to suppress the growth of structures at smaller (sub-galactic) scales [26,27]. Nor it is possible to define the quantum fluctuations to the (non-dynamical) field φ, so that the latter can provide the seeds of the observed large scale structure of the universe [22,23]. A reasonable supposition has therefore been to extend the CM theory further by incorporating higher derivative (HD) term(s) for φ, e.g. (✷φ) 2 , which lead(s) to a non-vanishing sound speed c s of the mimetic matter perturbations, keeping the background solution unaffected qualitatively 2 [22,23,29]. However, the HD terms in general make the theory susceptible to Ostrogradsky ghost or(and) gradient instabilities [26,27,[64][65][66][67], possible wayouts of which point to more complicated extensions...

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“…This issue is also closely related with one of our basic approximations-the stationarity of IDM flow. While the aforementioned non-perturbative effects substantially smoothen the IDM profile downstream from the Sun, singularities are not completely avoided 8 . The reason for this is the presence of the constraint (5), which effectively describes the potential flow of dust particles.…”

Section: Idm µνmentioning

confidence: 99%

Gravitational focusing of imperfect dark matter

Babichev

Ramazanov

2017

Phys. Rev. D

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Motivated by the projectable Horava-Lifshitz model/mimetic matter scenario, we consider a particular modification of standard gravity, which manifests as an imperfect low pressure fluid. While practically indistinguishable from a collection of nonrelativistic weakly interacting particles on cosmological scales, it leaves drastically different signatures in the Solar system. The main effect stems from gravitational focusing of the flow of Imperfect Dark Matter passing near the Sun. This entails strong amplification of Imperfect Dark Matter energy density compared to its average value in the surrounding halo. The enhancement is many orders of magnitude larger than in the case of Cold Dark Matter, provoking deviations of the metric in the second order in the Newtonian potential. Effects of gravitational focusing are prominent enough to substantially affect the planetary dynamics. Using the existing bound on the PPN parameter β P P N , we deduce a stringent constraint on the unique constant of the model.

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Initial conditions for imperfect dark matter

Abstract: We discuss initial conditions for the recently proposed Imperfect Dark Matter (Modified Dust). We show that they are adiabatic under fairly moderate assumptions about the cosmological evolution of the Universe at the relevant times.

Cited by 36 publications

References 40 publications

Living with ghosts in Hořava-Lifshitz gravity

Living with ghosts in Hořava-Lifshitz gravity

Cosmological dark sector from a mimetic–metric–torsion perspective

Gravitational focusing of imperfect dark matter

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