scholarly journals Hubble flow variations as a test for inhomogeneous cosmology

2019 ◽  
Vol 622 ◽  
pp. A83 ◽  
Author(s):  
Christoph Saulder ◽  
Steffen Mieske ◽  
Eelco van Kampen ◽  
Werner W. Zeilinger
Keyword(s):  
Large Scale ◽  
Cold Dark Matter ◽  
Statistical Tests ◽  
Specific Model ◽  
Accelerated Expansion ◽  
Inhomogeneous Cosmology ◽  
Galaxy Surveys ◽  
Model Versus ◽  
Differential Expansion ◽  
Hubble Flow

Context. Backreactions from large-scale inhomogeneities may provide an elegant explanation for the observed accelerated expansion of the universe without the need to introduce dark energy. Aims. We propose a cosmological test for a specific model of inhomogeneous cosmology, called timescape cosmology. Using large-scale galaxy surveys such as SDSS and 2MRS, we test the variation of expansion expected in the Λ-cold dark matter (Λ-CDM) model versus a more generic differential expansion using our own calibrations of bounds suggested by timescape cosmology. Methods. Our test measures the systematic variations of the Hubble flow towards distant galaxies groups as a function of the matter distribution in the lines of sight to those galaxy groups. We compare the observed systematic variation of the Hubble flow to mock catalogues from the Millennium Simulation in the case of the Λ-CDM model, and a deformed version of the same simulation that exhibits more pronounced differential expansion. Results. We perform a series of statistical tests, ranging from linear regressions to Kolmogorov-Smirnov tests, on the obtained data. They consistently yield results preferring Λ-CDM cosmology over our approximated model of timescape cosmology. Conclusions. Our analysis of observational data shows no evidence that the variation of expansion differs from that of the standard Λ-CDM model.

scholarly journals Comment on “Hubble flow variations as a test for inhomogeneous cosmology”

2019 ◽  
Vol 624 ◽  
pp. A12
Author(s):  
David L. Wiltshire
Keyword(s):  
Alternative Model ◽  
Inhomogeneous Cosmology ◽  
Cosmic Expansion ◽  
Standard Cosmology ◽  
Geometrical Features ◽  
Expansion Of The Universe ◽  
Expansion Model ◽  
Differential Expansion ◽  
The Universe ◽  
Hubble Flow

Saulder et al. (2019, A&A, 622, A83) have performed a novel observational test of the local expansion of the Universe for the standard cosmology as compared to an alternative model with differential cosmic expansion. Their analysis employs mock galaxy samples from the Millennium Simulation, a Newtonian N–body simulation on a ΛCDM background. For the differential expansion case the simulation has been deformed in an attempt to incorporate features of a particular inhomogeneous cosmology: the timescape model. It is shown that key geometrical features of the timescape cosmology have been omitted in this rescaling. Consequently, the differential expansion model tested by Saulder et al. (2019) cannot be considered to approximate the timescape cosmology.

scholarly journals Novel null-test for the Λ cold dark matter model with growth-rate data

2015 ◽  
Vol 24 (06) ◽  
pp. 1550045 ◽  
Author(s):  
Savvas Nesseris ◽  
Domenico Sapone
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Statistical Tests ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Late Time ◽  
Energy Component ◽  
Dark Energy Component ◽  
Standard Cosmological Model ◽  
Flrw Universe

Current and upcoming surveys will measure the cosmological parameters with an extremely high accuracy. The primary goal of these observations is to eliminate some of the currently viable cosmological models created to explain the late-time accelerated expansion (either real or only inferred). However, most of the statistical tests used in cosmology have a strong requirement: the use of a model to fit the data. Recently there has been an increased interest on finding tests that are model independent, i.e. to have a function that depends entirely on observed quantities and not on the model, see for instance [C. Clarkson, B. Bassett and T. H. C. Lu, Phys. Rev. Lett.101 (2008) 011301, arXiv:0712.3457 [astro-ph]]. In this paper, we present an alternative consistency check at the perturbative level for a homogeneous and isotropic Universe filled with a dark energy component. This test makes use of the growth of matter perturbations data and it is able to detect a deviation from the standard cosmological model, which could later be attributed to a clustering dark energy component, a tension in the data or a modification of gravity, within the framework of a Friedmann–Lemaître–Robertson–Walker (FLRW) universe.

scholarly journals A Study of co-existence between the Hubble flow and the random alignments of spin vectors of SDSS galaxies

BIBECHANA ◽  
2014 ◽  
Vol 12 ◽  
pp. 114-127
Author(s):  
Shiv Narayan Yadav ◽  
Walter Saurer ◽  
Binil Aryal
Keyword(s):  
Coordinate System ◽  
Galaxy Evolution ◽  
Spatial Orientation ◽  
Particle Physics ◽  
Large Scale ◽  
Statistical Tests ◽  
Azimuthal Angle ◽  
Three Dimensional ◽  
Simulation Method ◽  
Hubble Flow

We present a study of spin vector orientation of 14,118 SDSS (Sloan Digital Sky Survey) galaxies having redshift in the range 0.19 to 0.20 (radial velocity 57,000 km/s to 60,000 km/s) with respect to galactic coordinate system using 7th data release (2008, October). These galaxies were observed through SDSS telescope of Apache Point Observatory located at New Mexico, USA. The photometric database is made available through our collaboration with institute of Astro-particle physics, Innsbruck University, Austria. We used the `Godlowskian' method to convert two dimensional data to three dimensional galaxy rotation axes. Our intension is to find out non-random effects in the spatial orientation of galaxies and to check  redshift dependence. The expected isotropy distribution curves are obtained by removing the selection effects and performing a random simulation method. The observed and expected polar and azimuthal angle distributions are compared by using three statistical tests- chi-square, auto-correlation and the Fourier. It is found that the spatial orientation of galaxies tend to be oriented randomly with respect to the galactic coordinate system, supporting hierarchy model of galaxy evolution. In few cases we noticed a preference, probably due to the gravitational shearing or tidal effects in the large scale structure. In general, redshift is found to be independent of orientation. Hence, a very good correlation between the Hubble flow (redshift) and the random alignments of spin vectors of SDSS galaxies is noticed.DOI: http://dx.doi.org/10.3126/bibechana.v12i0.11787BIBECHANA 12 (2015) 114-127

scholarly journals On cosmology of interacting varying polytropic dark fluids

2019 ◽  
Vol 34 (17) ◽  
pp. 1950133
Author(s):  
Martiros Khurshudyan ◽  
Asatur Khurshudyan
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Dark Side ◽  
Model Parameters ◽  
Special Role ◽  
Large Scale Universe

In this paper, a possibility of the accelerated expansion of the large scale universe with interacting varying polytropic fluid of a certain type is presented. About a special role of non-gravitational interactions between dark energy and dark matter, in particular, about a possibility of improvement and solution of problems arising in modern cosmology, has been discussed for a long time. This motivates us to consider new models, where non-gravitational interactions between varying polytropic fluid and cold dark matter are allowed. Mainly nonlinear interactions of a specific type is considered, found in recent literature. The present study extends previously obtained results demonstrating that considered new parameterization of dark side of the universe could be supported by available observational data and will present the role of considered non-gravitational interactions in this case. During the study of suggested cosmological models Om analysis is applied. Moreover, with different datasets, including a strong gravitational lensing dataset, the best fit values of the model parameters are obtained using [Formula: see text] analysis.

scholarly journals Shell-crossing in a ΛCDM Universe

2020 ◽  
Vol 501 (1) ◽  
pp. L71-L75
Author(s):  
Cornelius Rampf ◽  
Oliver Hahn
Keyword(s):  
Dark Matter ◽  
Perturbation Theory ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Three Dimensional ◽  
Random Initial Data ◽  
Recursion Relations ◽  
Indispensable Tool ◽  
First Time ◽  
Very High

ABSTRACT Perturbation theory is an indispensable tool for studying the cosmic large-scale structure, and establishing its limits is therefore of utmost importance. One crucial limitation of perturbation theory is shell-crossing, which is the instance when cold-dark-matter trajectories intersect for the first time. We investigate Lagrangian perturbation theory (LPT) at very high orders in the vicinity of the first shell-crossing for random initial data in a realistic three-dimensional Universe. For this, we have numerically implemented the all-order recursion relations for the matter trajectories, from which the convergence of the LPT series at shell-crossing is established. Convergence studies performed at large orders reveal the nature of the convergence-limiting singularities. These singularities are not the well-known density singularities at shell-crossing but occur at later times when LPT already ceased to provide physically meaningful results.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

scholarly journals FORMATION OF DARK MATTER HALOES IN A HOMOGENEOUS DARK ENERGY UNIVERSE

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1397-1403
Author(s):  
L. MARASSI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
State Parameter ◽  
Mass Function ◽  
Accelerated Expansion ◽  
X Ray ◽  
Energy Models ◽  
Dark Energy Component ◽  
Standard Press

Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press–Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (power–law) mass function (where we apply a non-extensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is ω = -0.58, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the ω parameter is very sensible to modifications in the PL free parameter, q, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.

scholarly journals Using Stochastically Generated Subcolumns to Represent Cloud Structure in a Large-Scale Model

2006 ◽  
Vol 134 (12) ◽  
pp. 3644-3656 ◽  
Author(s):  
Robert Pincus ◽  
Richard Hemler ◽  
Stephen A. Klein
Keyword(s):  
Large Scale ◽  
Statistical Tests ◽  
Internal Variability ◽  
Cloud Fraction ◽  
Shortwave Radiation ◽  
Scale Model ◽  
Cloud Structure ◽  
Model Configuration ◽  
The Impact ◽  
Radiation Scheme

Abstract A new method for representing subgrid-scale cloud structure in which each model column is decomposed into a set of subcolumns has been introduced into the Geophysical Fluid Dynamics Laboratory’s global atmospheric model AM2. Each subcolumn in the decomposition is homogeneous, but the ensemble reproduces the initial profiles of cloud properties including cloud fraction, internal variability (if any) in cloud condensate, and arbitrary overlap assumptions that describe vertical correlations. These subcolumns are used in radiation and diagnostic calculations and have allowed the introduction of more realistic overlap assumptions. This paper describes the impact of these new methods for representing cloud structure in instantaneous calculations and long-term integrations. Shortwave radiation computed using subcolumns and the random overlap assumption differs in the global annual average by more than 4 W m−2 from the operational radiation scheme in instantaneous calculations; much of this difference is counteracted by a change in the overlap assumption to one in which overlap varies continuously with the separation distance between layers. Internal variability in cloud condensate, diagnosed from the mean condensate amount and cloud fraction, has about the same effect on radiative fluxes as does the ad hoc tuning accounting for this effect in the operational radiation scheme. Long simulations with the new model configuration show little difference from the operational model configuration, while statistical tests indicate that the model does not respond systematically to the sampling noise introduced by the approximate radiative transfer techniques introduced to work with the subcolumns.

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