Dark fluid or cosmological constant: Why there are different de Sitter-type spacetimes

Koohbor, Javad; Ramezani-Aval, H.

doi:10.1103/physrevd.91.063010

Cited by 10 publications

(23 citation statements)

References 18 publications

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“…13 As cold dark matter appears to do, in agreement with observations [39]. 14 The debate on the ability to distinguish ΛCDM from a dark fluid is still open [42].…”

Section: The Cosmographic Energy Conditionssupporting

confidence: 71%

On the theory and applications of modern cosmography

Dunsby

Luongo

2016

Int. J. Geom. Methods Mod. Phys.

157

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Cosmography represents an important branch of cosmology which aims to describe the universe without the need of postulating a priori any particular cosmological model. All quantities of interest are expanded as a Taylor series around here and now, providing in principle, a way of directly matching with cosmological data. In this way, cosmography can be regarded a model-independent technique, able to fix cosmic bounds, although several issues limit its use in various model reconstructions. The main purpose of this review is to focus on the key features of cosmography, emphasising both the strategy for obtaining the observable cosmographic series and pointing out any drawbacks which might plague the standard cosmographic treatment. In doing so, we relate cosmography to the most relevant cosmological quantities and to several dark energy models. We also investigate whether cosmography is able to provide information about the form of the cosmological expansion history, discussing how to reproduce the dark fluid from the cosmographic sound speed. Following this, we discuss limits on cosmographic priors and focus on how to experimentally treat cosmographic expansions. Finally, we present some of the latest developments of the cosmographic method, reviewing the use of rational approximations, based on cosmographic Padé polynomials. Future prospects leading to more accurate cosmographic results, able to better reproduce the expansion history of the universe are also discussed in detail.

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“…13 As cold dark matter appears to do, in agreement with observations [39]. 14 The debate on the ability to distinguish ΛCDM from a dark fluid is still open [42].…”

Section: The Cosmographic Energy Conditionssupporting

confidence: 71%

On the theory and applications of modern cosmography

Dunsby

Luongo

2016

Int. J. Geom. Methods Mod. Phys.

157

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“…But they were found to be genuinely different from de Sitter space, when their curvature invariants as well as their dynamical forms in the comoving synchronous coordinate systems were calculated. These findings motivated the idea that one should consider a perfect fluid nature for the cosmological term and assign a 4-velocity to the fluid particles, in order to be able to interpret the preferred directional expansion of the de Sitter-type spacetimes in their dynamical forms [3].…”

Section: Introductionmentioning

confidence: 79%

“…Indeed this case has been thoroughly discussed in [3], where it is shown that it leads to a unique characterization of de Sitter and de Sitter-type spacetimes as the only one-component static perfect fluid solutions of Einstein field equations in a non-comoving frame. The well known de sitter spacetime…”

Section: Static and Stationary Perfect Fluid Solutionsmentioning

confidence: 99%

“…Interestingly enough we will find out that in some cases the sign of the cosmological constant, or equivalently ρ Λ , is fixed by our choice of the GEM fields. Indeed, as an interesting example of the above characterization, it has already been shown that the de Sitter space, and the so called de Sitter-type spacetimes are the only static single-component perfect fluid solutions of EFE in the non-comoving frames [3]. Characterizing them in this way, the apparent paradox raised by some authors [4,5] on why there are different static spacetimes with Λ as their only parameter was resolved.…”

Section: Introductionmentioning

confidence: 95%

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Static and stationary dark fluid universes: A gravitoelectromagnetic perspective

Nouri-Zonoz¹

2020

Preprint

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We introduce a physical characterization of the static and stationary perfect fluid solutions of the Einstein field equations with a single or 2-component perfect fluid sources, according to their gravitoelectric and gravitomagnetic fields. The absence or presence of either or both of these fields could restrict the equations of state of the underlying perfect fluid sources. As an example and representative of each class we consider solutions that include the cosmological term as a fluid source with the equation of state p = −ρ = constant. All these solutions share the feature that go over smoothly into the Minkowski spacetime as Λ → 0.

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“…Hawking modes from the de sitter cosmological horizon W begin the examples of this section with the de Sitter cosmological horizon, while for a discussion of the comparative physics of the de Sitter spacetime in static and dynamic patches we refer to [32]. The static patch of the de Sitter spacetime is defined by the metric, ds r dt r dr r d 1 3 1 3…”

Section: 1mentioning

confidence: 99%

Hawking modes and the optimal disperser: holographic lessons from the observer's causal-patch unitarity

Koohbor

Tavanfar

2018

J. Phys. Commun.

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Based on an observer-centric methodology, we pinpoint the basic origin of the spectral Planckianity of the asymptotic Hawking modes in the conventional treatments of the evaporating horizons. By considering an observer who analyzes a causal horizon in a generic spacetime, we first clarify how the asymptotic Planckian spectrum is imposed on the exponentially redshifted Hawking modes through a geometric dispersion mechanism developed by a semiclassical environment which is composed by all the modes that build up the curvature of the causal patch of the asymptotic observer. We also discuss the actual microscopic phenomenon of the Hawking evaporation of generic causal horizons. Our quantum description is based on a novel holographic scheme of gravitational open quantum systems in which the degrees of freedom that build up the curvature of the observer's causal patch interact with the radiated Hawking modes, initially as environmental quanta, and after a crossover time, as quantum defects. Planckian dispersion of the modes would only be developed in the strict thermodynamic limit of this quantum environment, called optimal disperser, which is nevertheless avoided holographically. Finally, we outline and characterize how our microscopic formulation of the observer-centric holography, beyond the AdS/CFT examples and for generic causal patches, does realize the information-theoretic processing of unitarity.

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Dark fluid or cosmological constant: Why there are different de Sitter-type spacetimes

Cited by 10 publications

References 18 publications

On the theory and applications of modern cosmography

On the theory and applications of modern cosmography

Static and stationary dark fluid universes: A gravitoelectromagnetic perspective

Hawking modes and the optimal disperser: holographic lessons from the observer's causal-patch unitarity

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