scholarly journals Observational tests for oscillating expansion rate of the Universe

2010 ◽  
Vol 82 (10) ◽  
Author(s):  
Koichi Hirano ◽  
Zen Komiya
Keyword(s):  
Expansion Rate ◽  
The Universe

scholarly journals Model-independent cosmic acceleration and redshift-dependent intrinsic luminosity in type-Ia supernovae

2019 ◽  
Vol 625 ◽  
pp. A15 ◽  
Author(s):  
I. Tutusaus ◽  
B. Lamine ◽  
A. Blanchard
Keyword(s):  
Spline Interpolation ◽  
High Redshift ◽  
Cosmic Acceleration ◽  
Expansion Rate ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Model Independent ◽  
Ia Supernovae ◽  
The Universe ◽  
Intrinsic Luminosity

Context. The cosmological concordance model (ΛCDM) is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type-Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has been some debate in the literature concerning the statistical treatment of SNIa, and their stature as proof of cosmic acceleration. Aims. In this paper we relax the standard assumption that SNIa intrinsic luminosity is independent of redshift, and examine whether it may have an impact on our cosmological knowledge and more precisely on the accelerated nature of the expansion of the universe. Methods. To maximise the scope of this study, we do not specify a given cosmological model, but we reconstruct the expansion rate of the universe through a cubic spline interpolation fitting the observations of the different cosmological probes: SNIa, baryon acoustic oscillations (BAO), and the high-redshift information from the cosmic microwave background (CMB). Results. We show that when SNIa intrinsic luminosity is not allowed to vary as a function of redshift, cosmic acceleration is definitely proven in a model-independent approach. However, allowing for redshift dependence, a nonaccelerated reconstruction of the expansion rate is able to fit, at the same level of ΛCDM, the combination of SNIa and BAO data, both treating the BAO standard ruler rd as a free parameter (not entering on the physics governing the BAO), and adding the recently published prior from CMB observations. We further extend the analysis by including the CMB data. In this case we also consider a third way to combine the different probes by explicitly computing rd from the physics of the early universe, and we show that a nonaccelerated reconstruction is able to nicely fit this combination of low- and high-redshift data. We also check that this reconstruction is compatible with the latest measurements of the growth rate of matter perturbations. We finally show that the value of the Hubble constant (H0) predicted by this reconstruction is in tension with model-independent measurements. Conclusions. We present a model-independent reconstruction of a nonaccelerated expansion rate of the universe that is able to fit all the main background cosmological probes nicely. However, the predicted value of H0 is in tension with recent direct measurements. Our analysis points out that a final reliable and consensual value for H0 is critical to definitively prove cosmic acceleration in a model-independent way.

Formation of the initial distribution of matter inhomogeneities in the era of radiation domination

2015 ◽  
Vol 12 (09) ◽  
pp. 1550097 ◽  
Author(s):  
Yuriy A. Portnov
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Initial Distribution ◽  
Elementary Particles ◽  
Expansion Rate ◽  
Material Inhomogeneity ◽  
Universe Expansion ◽  
Primary Material ◽  
The Future ◽  
The Universe

This paper considers the dependence of the Universe expansion rate in the era of radiation domination of the orbital angular momentum of photons filling the Universe. It is shown that the presence of a nonzero orbital angular momentum in photons leads to increase in the rate of expansion. As a consequence, the hypothesis is made that areas of the Universe, having photons with nonzero orbital angular momentum inside them, will cool faster. In these areas the elementary particles will form earlier, compared to the rest of the Universe. Therefore, these areas become the future centers of the primary material inhomogeneity.

scholarly journals Resolving the Hubble Constant Discrepancy: Revisiting the Effect of Local Environments

2020 ◽  
Vol 2 (1) ◽  
pp. 94-96
Author(s):  
Dennis M Doren ◽  
James Harasymiw
Keyword(s):  
Mass Density ◽  
Hubble Constant ◽  
Local Environment ◽  
Expansion Rate ◽  
Local Environments ◽  
The Universe

Studies have found two differing sets of figures for the Hubble constant without clear direction for resolution of that difference. This article offers a direction for reconciling the measurement discrepancy. Research is reviewed and theory is described that indicate the resolution may be found in revisiting how the degree of mass in local environments affects computations. The idea that the expansion rate of the universe is invariably uniform is discounted, to be replaced by a range of figures depending on the mass density of the local environment underlying the measurement.

Dark Matter

2021 ◽  
pp. 66-78
Author(s):  
Gianfranco Bertone
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Waves ◽  
Expansion Rate ◽  
The Earth ◽  
Modern Cosmology ◽  
Large Effort ◽  
The Universe

I introduce here the problem of dark energy, a substance that appears to be pushing the Universe to expand ever faster and discuss the large effort currently in place to understand its origin. I describe the surprising recent discovery of a widening crack in the cathedral of modern cosmology arising from the measurement of the expansion rate of the Universe. And I argue that gravitational waves observations can help us to either repair that crack, or to bring down that magnificent building, in case it turns out to be fatally flawed. Before all women and all men. Before animals, plants, archaeans, bacteria. Before the Earth was formed and the stars were lit. Before everything we know, the Universe was immersed in an amorphous and oblivious darkness.

scholarly journals New constraints on cosmological parameters and neutrino properties using the expansion rate of the Universe toz∼ 1.75

2012 ◽  
Vol 2012 (07) ◽  
pp. 053-053 ◽  
Author(s):  
Michele Moresco ◽  
Licia Verde ◽  
Lucia Pozzetti ◽  
Raul Jimenez ◽  
Andrea Cimatti
Keyword(s):  
Cosmological Parameters ◽  
Expansion Rate ◽  
The Universe

scholarly journals The expansion rate of the universe

2002 ◽  
Vol 43 (1) ◽  
pp. 1.10-1.13
Author(s):  
Wendy Freedman
Keyword(s):  
Expansion Rate ◽  
The Universe

scholarly journals THE EFFECT OF STRUCTURE FORMATION ON THE EXPANSION OF THE UNIVERSE

2008 ◽  
Vol 17 (13n14) ◽  
pp. 2543-2548 ◽  
Author(s):  
SYKSY RÄSÄNEN
Keyword(s):  
Structure Formation ◽  
Cold Dark Matter ◽  
Expansion Rate ◽  
Isotropic Case ◽  
Isotropic Distribution ◽  
Expansion Of The Universe ◽  
Free Parameters ◽  
Matter Transfer ◽  
The Universe ◽  
Dust Universe

Observations of the expansion rate of the universe at late times disagree by a factor of 1.5–2 with the prediction of homogeneous and isotropic models based on ordinary matter and gravity. We discuss how the departure from linearly perturbed homogeneity and isotropy due to structure formation could explain this discrepancy. We evaluate the expansion rate in a dust universe which contains nonlinear structures with a statistically homogeneous and isotropic distribution. The expansion rate is found to increase relative to the exactly homogeneous and isotropic case by a factor of 1.1–1.3 at some tens of billions of years. The time scale follows from the cold dark matter transfer function and the amplitude of primordial perturbations without additional free parameters.

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