Observable quantities in cosmological models with strings

Dąbrowski, Mariusz P.; Stelmach, Jerzy

doi:10.1086/115041

Cited by 30 publications

(41 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…More precise fit to the data shows that at least 70% of matter in the universe now has negative pressure and it is neither the visible matter, nor the dark matter, which can sum up to the remaining 30%. Some possible sources of negative pressure had already been suggested before 1998 and they were: the cosmological constant w = −1 [8], cosmic strings w = −1/3, and domain walls w = −2/3 [9,10]. In fact, this result gives more evidence for an asymptotic emptiness in the future of the universe described by the de Sitter model in which → 0 when a = exp [( Λ/3)t] → ∞.…”

Section: Empty Future Big-crunch and Phantom-driven Big-ripmentioning

confidence: 99%

Future state of the universe

Dąbrowski

2006

Ann. Phys.

View full text Add to dashboard Cite

Following the observational evidence for cosmic acceleration which may exclude a possibility for the universe to recollapse to a second singularity, we review alternative scenarios of its future evolution. Although the de Sitter asymptotic state is still an option, some other asymptotic states which allow new types of singularities such as Big-Rip (due to a phantom matter) and sudden future singularities are also admissible and are reviewed in detail. The reality of these singularities which comes from the relation to observational characteristics of the universe expansion are also revealed and widely discussed.

show abstract

Section: Empty Future Big-crunch and Phantom-driven Big-ripmentioning

confidence: 99%

Future state of the universe

Dąbrowski

2006

Ann. Phys.

View full text Add to dashboard Cite

show abstract

“…In other words, we have a position-dependent 'equation of state' of the form p = − 1 3 µc 2 + ǫ(χ)µ 1/2 . The appearance of − 1 3 µ as the dominant contribution (at early times, at least, when R is small so that, from (15), µ is large) immediately suggests a quintessential or scalar field interpretation of the matter [44][45][46][47], although it has been shown [52,53] that cosmic strings also give rise to this EOS. Although the energy-momentum tensor of the Stephani models has the perfect fluid form, the interpretation of the matter as an actual fluid is by no means required; other interpretations may also be valid, and the fact that there is no true EOS might even suggest a two-component interpretation.…”

Section: Matter Content and Energy Conditionsmentioning

confidence: 99%

Undermining the cosmological principle: almost isotropic observations in inhomogeneous cosmologies

Barrett

Clarkson

2000

Class. Quantum Grav.

View full text Add to dashboard Cite

We challenge the widely held belief that the cosmological principle is an obvious consequence of the observed isotropy of the cosmic microwave background radiation (CMB), combined with the Copernican principle. We perform a detailed analysis of a class of inhomogeneous perfect fluid cosmologies admitting an isotropic radiation field, with a view to assessing their viability as models of the real universe. These spacetimes are distinguished from FLRW universes by the presence of inhomogeneous pressure, which results in an acceleration of the fluid (fundamental observers). We examine their physical, geometrical and observational characteristics for all observer positions in the spacetimes. To this end, we derive exact, analytic expressions for the distance-redshift relations and anisotropies for any observer, and compare their predictions with available observational constraints. As far as the authors are aware, this work represents the first exact analysis of the observational properties of an inhomogeneous cosmological model for all observer positions. Considerable attention is devoted to the anisotropy in the CMB. The difficulty of defining the surface of last scattering in exact, inhomogenous cosmological models is discussed; several alternative practical definitions are presented, and one of these is used to estimate the CMB anisotropy for any model. The isotropy constraints derived from 'local' observations (redshift < ∼ 1) are also considered, qualitatively. A crucial aspect of this work is the application of the Copernican principle: for a specific model to be acceptable we demand that it must be consistent with current observational constraints (especially anisotropy constraints) for all observer locations. The most important results of the paper are presented as exclusion plots in the 2-D parameter space of the models. We show that there is a region of parameter space not ruled out by the constraints we consider and containing models that are significantly inhomogeneous. It follows immediately from this that the cosmological principle cannot be assumed to hold on the basis of present observational constraints. *

show abstract

“…In order to study observational tests we now define dimensionless observational density parameters [10,11] …”

mentioning

confidence: 99%

“…This case was already presented in a different framework in Ref. [11]. Secondly, we will study the case γ = −1/3 (dark energy on the brane [5] -we will label this type of matter with Ω d instead of Ω GR ).…”

mentioning

confidence: 99%

Brane Universes Tested Against Astronomical Data

Dąbrowski¹,

Godlowski²,

Szydłowski³

2004

Int. J. Mod. Phys. D

Self Cite

View full text Add to dashboard Cite

We discuss observational constrains coming from supernovae Ia [3] imposed on the behaviour of the Randall-Sundrum models. In the case of dust matter on the brane, the difference between the best-fit general relativistic model with a Λ-term [3] and the best-fit brane models becomes detectable for redshifts z > 0.6. It is interesting that brane models predict brighter galaxies for such redshifts which is in agreement with the measurement of the z = 1.7 supernova [6] and with the New Data from the High Z Supernovae Search Team [7]. We also demonstrate that the fit to supernovae data can also be obtained, if we admit the "super-negative" dark energy p = −(4/3)̺ on the brane, where the dark energy in a way mimics the influence of the cosmological constant. It also appears that the dark energy enlarges the age of the universe which is demanded in cosmology. Finally, we propose to check for dark radiation and brane tension by the application of the angular diameter of galaxies minimum value test. The idea of brane universes has originated from Hořava and Witten [1] followed by Randall and Sundrum [2]. Brane models admit new parameters which are not present in standard cosmology (brane tension λ and dark radiation U). From the astronomical observations of supernovae Ia [3, 4] one knows that the universe is now accelerating and the best-fit model is for the 4-dimensional cosmological constant density parameter Ω Λ (4) ,0 = 0.72 and for the dust density parameter Ω m,0 = 0.28 (index "0" refers to the present moment of time). In other words, only the exotic (negative pressure) matter in standard cosmology can lead to this global effect. On the other hand, in brane models the ̺ 2 quadratic contribution in the energy density even for a small negative pressure, contributes effectively as the positive pressure, and makes brane models less accelerating. In this paper we argue that in order to avoid this problem

show abstract

Observable quantities in cosmological models with strings

Cited by 30 publications

References 26 publications

Future state of the universe

Future state of the universe

Undermining the cosmological principle: almost isotropic observations in inhomogeneous cosmologies

Brane Universes Tested Against Astronomical Data

Contact Info

Product

Resources

About