Special Issue "Cosmology with Fluid Components"

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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (31 December 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Iver Brevik (Website)

Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Phone: +47 7359 3555
Interests: viscous cosmology; multcomponent fluids; modified gravity and fluids; fluids and branes; electromagnetic aspects in the cosmic fluid

Special Issue Information

Dear Colleagues,

Recent investigations in general relativity and cosmology have shown the usefulness of taking into account realistic properties of the cosmic fluid, such as viscosity (shear and bulk), turbulence, multicomponent properties, etc. The objective of the present volume is to focus on these kind of properties, from different viewpoints, therewith adding to the physical understanding of the cosmic fluid. We would like like to call for papers disseminating and sharing recent findings on a diversity of topics, including but not restricted to:

  • viscous cosmology
  • turbulence
  • the role of viscosity in regard to the phantom/quintessence epochs
  • multicomponent fluids
  • future singularities
  • entropy issues
  • the role of the Casimir effect in cosmology
  • modified gravity
  • electromagnetic effects in the cosmic fluid

Also, review papers are welcome.

Prof. Dr. Iver Brevik
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. For the first couple of issues the Article Processing Charge (APC) will be waived for well-prepared manuscripts. English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.


Published Papers (9 papers)

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Research

Jump to: Review

Open AccessArticle A Toy Cosmology Using a Hubble-Scale Casimir Effect
Galaxies 2014, 2(1), 81-88; doi:10.3390/galaxies2010081
Received: 29 December 2013 / Revised: 7 February 2014 / Accepted: 13 February 2014 / Published: 19 February 2014
Cited by 1 | PDF Full-text (158 KB) | HTML Full-text | XML Full-text
Abstract
The visible mass of the observable universe agrees with that needed for a flat cosmos, and the reason for this is not known. It is shown that this can be explained by modelling the Hubble volume as a black hole that emits [...] Read more.
The visible mass of the observable universe agrees with that needed for a flat cosmos, and the reason for this is not known. It is shown that this can be explained by modelling the Hubble volume as a black hole that emits Hawking radiation inwards, disallowing wavelengths that do not fit exactly into the Hubble diameter, since partial waves would allow an inference of what lies outside the horizon. This model of “horizon wave censorship” is equivalent to a Hubble-scale Casimir effect. This incomplete toy model is presented to stimulate discussion. It predicts a minimum mass and acceleration for the observable universe which are in agreement with the observed mass and acceleration, and predicts that the observable universe gains mass as it expands and was hotter in the past. It also predicts a suppression of variation on the largest cosmic scales that agrees with the low-l cosmic microwave background anomaly seen by the Planck satellite. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessArticle Cosmographic Constraints and Cosmic Fluids
Galaxies 2013, 1(3), 216-260; doi:10.3390/galaxies1030216
Received: 10 September 2013 / Revised: 6 November 2013 / Accepted: 12 November 2013 / Published: 4 December 2013
Cited by 19 | PDF Full-text (595 KB) | HTML Full-text | XML Full-text
Abstract
The problem of reproducing dark energy effects is reviewed here with particular interest devoted to cosmography. We summarize some of the most relevant cosmological models, based on the assumption that the corresponding barotropic equations of state evolve as the universe expands, giving [...] Read more.
The problem of reproducing dark energy effects is reviewed here with particular interest devoted to cosmography. We summarize some of the most relevant cosmological models, based on the assumption that the corresponding barotropic equations of state evolve as the universe expands, giving rise to the accelerated expansion. We describe in detail the ΛCDM (Λ-Cold Dark Matter) and ωCDM models, considering also some specific examples, e.g., Chevallier–Polarsky–Linder, the Chaplygin gas and the Dvali–Gabadadze–Porrati cosmological model. Finally, we consider the cosmological consequences of f(R) and f(T) gravities and their impact on the framework of cosmography. Keeping these considerations in mind, we point out the model-independent procedure related to cosmography, showing how to match the series of cosmological observables to the free parameters of each model. We critically discuss the role played by cosmography, as a selection criterion to check whether a particular model passes or does not present cosmological constraints. In so doing, we find out cosmological bounds by fitting the luminosity distance expansion of the redshift, z, adopting the recent Union 2.1 dataset of supernovae, combined with the baryonic acoustic oscillation and the cosmic microwave background measurements. We perform cosmographic analyses, imposing different priors on the Hubble rate present value. In addition, we compare our results with recent PLANCK limits, showing that the ΛCDM and ωCDM models seem to be the favorite with respect to other dark energy models. However, we show that cosmographic constraints on f(R) and f(T) cannot discriminate between extensions of General Relativity and dark energy models, leading to a disadvantageous degeneracy problem. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessArticle Conformally Coupled Inflation
Galaxies 2013, 1(2), 96-106; doi:10.3390/galaxies1020096
Received: 29 June 2013 / Revised: 19 July 2013 / Accepted: 19 July 2013 / Published: 30 July 2013
Cited by 1 | PDF Full-text (194 KB) | HTML Full-text | XML Full-text
Abstract
A massive scalar field in a curved spacetime can propagate along the light cone, a causal pathology, which can, in principle, be eliminated only if the scalar couples conformally to the Ricci curvature of spacetime. This property mandates conformal coupling for the [...] Read more.
A massive scalar field in a curved spacetime can propagate along the light cone, a causal pathology, which can, in principle, be eliminated only if the scalar couples conformally to the Ricci curvature of spacetime. This property mandates conformal coupling for the field driving inflation in the early universe. During slow-roll inflation, this coupling can cause super-acceleration and, as a signature, a blue spectrum of primordial gravitational waves. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessArticle Inhomogeneous Viscous Fluids in a Friedmann-Robertson-Walker (FRW) Universe
Galaxies 2013, 1(2), 83-95; doi:10.3390/galaxies1020083
Received: 20 May 2013 / Revised: 26 June 2013 / Accepted: 27 June 2013 / Published: 9 July 2013
Cited by 6 | PDF Full-text (253 KB) | HTML Full-text | XML Full-text
Abstract
We give a brief review of some aspects of inhomogeneous viscous fluids in a flat Friedmann-Robertson-Walker Universe. In general, it is pointed out that several fluid models may bring the future Universe evolution to become singular, with the appearance of the so-called [...] Read more.
We give a brief review of some aspects of inhomogeneous viscous fluids in a flat Friedmann-Robertson-Walker Universe. In general, it is pointed out that several fluid models may bring the future Universe evolution to become singular, with the appearance of the so-called Big Rip scenario. We investigate the effects of fluids coupled with dark matter in a de Sitter Universe, by considering several cases. Due to this coupling, the coincidence problem may be solved, and if the de Sitter solution is stable, the model is also protected against the Big Rip singularity. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessArticle Cosmological Observations in a Modified Theory of Gravity (MOG)
Galaxies 2013, 1(1), 65-82; doi:10.3390/galaxies1010065
Received: 10 May 2013 / Accepted: 15 June 2013 / Published: 20 June 2013
Cited by 9 | PDF Full-text (335 KB) | HTML Full-text | XML Full-text
Abstract
Our Modified Gravity Theory (MOG) is a gravitational theory without exotic dark matter, based on an action principle. MOG has been used successfully tomodel astrophysical phenomena, such as galaxy rotation curves, galaxy cluster masses and lensing. MOG may also be able to [...] Read more.
Our Modified Gravity Theory (MOG) is a gravitational theory without exotic dark matter, based on an action principle. MOG has been used successfully tomodel astrophysical phenomena, such as galaxy rotation curves, galaxy cluster masses and lensing. MOG may also be able to account for cosmological observations. We assume that the MOG point source solution can be used to describe extended distributions of matter via an appropriately modified Poisson equation. We use this result to model perturbation growth in MOG and find that it agrees well with the observed matter power spectrum at present. As the resolution of the power spectrum improves with increasing survey size, however, significant differences emerge between the predictions of MOG and the standard Λ-cold dark matter (Λ-CDM) model, as in the absence of exotic darkmatter, oscillations of the power spectrum in MOG are not suppressed. We can also use MOG to model the acoustic power spectrum of the cosmic microwave background. A suitably adapted semi-analytical model offers a first indication that MOG may pass this test and correctly model the peak of the acoustic spectrum. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessArticle Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations
Galaxies 2013, 1(1), 31-43; doi:10.3390/galaxies1010031
Received: 15 April 2013 / Revised: 22 May 2013 / Accepted: 23 May 2013 / Published: 29 May 2013
Cited by 2 | PDF Full-text (520 KB) | HTML Full-text | XML Full-text
Abstract
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis [...] Read more.
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Figures

Open AccessArticle Exact Expressions for the Pericenter Precession Caused by Some Dark Matter Distributions and Constraints on Them from Orbital Motions in the Solar System, in the Double Pulsar and in the Galactic Center
Galaxies 2013, 1(1), 6-30; doi:10.3390/galaxies1010006
Received: 24 April 2013 / Revised: 16 May 2013 / Accepted: 16 May 2013 / Published: 28 May 2013
Cited by 18 | PDF Full-text (446 KB) | HTML Full-text | XML Full-text
Abstract
We analytically calculate the secular precession of the pericenter of a test particle orbiting a central body surrounded by a continuous distribution of Dark Matter (DM) by using some commonly adopted spherically symmetric density profiles for it. We obtain exact expressions without [...] Read more.
We analytically calculate the secular precession of the pericenter of a test particle orbiting a central body surrounded by a continuous distribution of Dark Matter (DM) by using some commonly adopted spherically symmetric density profiles for it. We obtain exact expressions without resorting to a-priori simplifying assumptions on the orbital geometry of the test particle. Our formulas allow us to put constraints on the parameters of the DM distributions considered in several local astronomical and astrophysical scenarios, such as the Sun's planetary system, the double pulsar, and the stellar system around the supermassive black hole in Sgr A, all characterized by a wide variety of orbital configuratio ns. As far as our Solar System is concerned, latest determinations of the supplementary perihelion precessions ̟˙ with the EPM2011 ephemerides and the common power-law DM density profile ρDM(r) = ρ0rγ λγ yield 5 × 103 GeV cm−3 (γ = 0) ≤ ρ0 ≤ 8 × 103 GeV cm−3 (γ = 4), corresponding to 8.9 × 10−21 g cm−3 ≤ ρ0 ≤ 1.4 × 10−20 g cm−3, at the Saturn's distance. From the periastron of the pulsar PSR J0737-3039A and the same power-low DM density, one has 1.7 × 1016 GeV cm−3 (γ = 0) ≤ ρ0 ≤ 2 × 1016 (γ = 4) GeV cm−3, corresponding to 3.0 × 10−8 g cm−3 ≤ ρ0 ≤ 3.6 × 10−8 g cm−3. The perinigricon of the S0-2 star in Sgr A and the power-law DM model give 1.2 × 1013 GeV cm−3 (γ = 0) ≤ ρ0 ≤ 1 × 1016 (γ = 4, λ = rmin) GeV cm−3, corresponding to 2.1 × 10−11 g cm−3 ≤ ρ0 ≤ 1.8 × 10−8 g cm−3. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)

Review

Jump to: Research

Open AccessReview Large Scale Cosmological Anomalies and Inhomogeneous Dark Energy
Galaxies 2014, 2(1), 22-61; doi:10.3390/galaxies2010022
Received: 6 November 2013 / Revised: 24 December 2013 / Accepted: 25 December 2013 / Published: 17 January 2014
Cited by 9 | PDF Full-text (1274 KB) | HTML Full-text | XML Full-text
Abstract
A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic [...] Read more.
A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic Microwave Background perturbations on large angular scales, large dipolar peculiar velocity flows of galaxies (“bulk flows”), the measurement of inhomogenous values of the fine structure constant on cosmological scales (“alpha dipole”) and other effects. The presence of the observational anomalies could either be a large statistical fluctuation in the context of ΛCDM or it could indicate a non-trivial departure from the cosmological principle on Hubble scales. Such a departure is very much constrained by cosmological observations for matter. For dark energy however there are no significant observational constraints for Hubble scale inhomogeneities. In this brief review I discuss some of the theoretical models that can naturally lead to inhomogeneous dark energy, their observational constraints and their potential to explain the large scale cosmic anomalies. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)
Open AccessReview Rip Cosmology via Inhomogeneous Fluid
Galaxies 2013, 1(2), 107-113; doi:10.3390/galaxies1020107
Received: 31 July 2013 / Revised: 10 August 2013 / Accepted: 12 August 2013 / Published: 15 August 2013
PDF Full-text (206 KB) | HTML Full-text | XML Full-text
Abstract The conditions for the appearance of the Little Rip, Pseudo Rip and Quasi Rip universes in the terms of the parameters in the equation of state of some dark fluid are investigated. Several examples of the Rip cosmologies are investigated. Full article
(This article belongs to the Special Issue Cosmology with Fluid Components)

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