Values Of Ωm Research Articles

Elucidating the z-dependence of the MOND acceleration (a0) within the scale invariant vacuum (SIV) paradigm

ABSTRACT In a recent paper: “On the time dependency of $a_0$” the authors claim that they have tested “one of the predictions of the Scale Invariant Vacuum (SIV) theory on MOND” by studying the dependence of the Modified Newtonian Dynamics (MOND) acceleration at two data sets, low-z ($3.2\times 10^{-4}\le z\le 3.2\times 10^{-2}$) and high-z ($0.5\le z\le 2.5$). They claim “both samples show a dependency of $a_0$ from z”. Here, the work mentioned above is revisited. The explicit analytic expression for the z-dependence of the $a_0$ within the SIV theory is given. Furthermore, the first estimates of the $\Omega _m$ within SIV theory give $\Omega _{m}=0.28\pm 0.04$ using the low-z data only, while a value of $\Omega _{m}=0.055$ is obtained using both data sets. This much lower $\Omega _m$ leaves no room for non-baryonic matter! Unlike in the mentioned paper above, the slope in the z-dependence of $A_0=\log _{10}(a_0)$ is estimated to be consistent with zero Z-slope for the two data sets. Finally, the statistics of the data are consistent with the SIV predictions; in particular, the possibility of change in the sign of the slopes for the two data sets is explainable within the SIV paradigm; however, the uncertainty in the data is too big for the clear demonstration of a z-dependence yet.

ΛCDM is alive and well

Despite its successes, the ΛCDM model faces several tensions with recent cosmological data and their increased accuracy. The mismatch between the values of the Hubble constant H0 obtained from {some} direct distance ladder measurements and from the cosmic microwave background (CMB) is the most statistically significant, but the amplitude of the matter fluctuations is also regarded as a serious concern, leading to the investigation of a plethora of {alternative} models. Here, we examine the situation from a different perspective. We first show that the combination of several recent measurements from local probes leads to a tight constraint on the present-day matter density Ωm as well as on the amplitude of the matter fluctuations, both acceptably consistent with the values inferred from the CMB. Secondly, we address the Hubble tension by assuming that some determinations of the value of H0 are possibly biased. We treat such a bias as a nuisance parameter within ΛCDM and we examine such `` ΛCDM + H0 bias’’ models on the same statistical grounds as alternative cosmological models. A bias in Planck or in SH0ES produces similar improvements. However we show that a bias in the Cepheids calibration produces improvements in terms of ΔAIC that supersede existing extended models proposed up to now. In a third step, we show that the value of Ωm we obtained from our RSD, Pantheon+ and 3×2pt from DES, combined with SH0ES determination of H0, leads to a precise determination of the density parameter of the Universe ωm=0.1753±0.0069. This measurement provides an additional low-redshift test for cosmological models by comparing it to the preferred value derived from the CMB. From this test, most ΛCDM extensions seem to be confronted with a new tension as many of them cluster around ωm=0.14, while there is no tension with a local $H_0 67 $ km/s/Mpc. We conclude that a standard ΛCDM model with an unknown bias in the Cepheids distance calibration represents a model that reaches a remarkable agreement, statistically better than previously proposed extensions without bias for which such a comparison can be performed.

UNIONS: The impact of systematic errors on weak-lensing peak counts

Context. The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is an ongoing deep photometric multiband survey of the northern sky. As part of UNIONS, the Canada-France Imaging Survey (CFIS) provides r-band data, which we use to study weak-lensing peak counts for cosmological inference. Aims. We assess systematic effects for weak-lensing peak counts and their impact on cosmological parameters for the UNIONS survey. In particular, we present results on local calibration, metacalibration shear bias, baryonic feedback, the source galaxy redshift estimate, intrinsic alignment, and cluster member dilution. Methods. For each uncertainty and systematic effect, we describe our mitigation scheme and the impact on cosmological parameter constraints. We obtain constraints on cosmological parameters from Monte Carlo Markov chains using CFIS data and MassiveNuS N-body simulations as a model for peak counts statistics. Results. Depending on the calibration (local versus global, and the inclusion or not of the residual multiplicative shear bias), the mean matter density parameter, Ωm, can shift by up to −0.024 (−0.5σ). We also see that including baryonic corrections can shift Ωm by +0.027 (+0.5σ) with respect to the dark-matter-only simulations. Reducing the impact of the intrinsic alignment and cluster member dilution through signal-to-noise cuts leads to larger constraints. Finally, with a mean redshift uncertainty of Δz̄ = 0.03, we see that the shift in Ωm (+0.001, which corresponds to +0.02σ) is not significant. Conclusions. This paper investigates, for the first time with UNIONS weak-lensing data and peak counts, the impact of systematic effects. The value of Ωm is the most impacted and can shift by up to ∼0.03, which corresponds to 0.5σ depending on the choices for each systematics. We expect constraints to become more reliable with future (larger) data catalogs, for which the current pipeline will provide a starting point. The code used to obtain the results is available on GitHub.

Artificial neural networks for galaxy clustering: Learning from the two-point correlation function of BOSS galaxies

The increasingly large amount of cosmological data coming from ground-based and space-borne telescopes requires highly efficient and fast enough data analysis techniques to maximise the scientific exploitation. In this work, we explore the capabilities of supervised machine learning algorithms to learn the properties of the large-scale structure of the Universe, aiming at constraining the matter density parameter, Ωm. We implement a new Artificial Neural Network for a regression data analysis, and train it on a large set of galaxy two-point correlation functions in standard cosmologies with different values of Ωm. The training set is constructed from log-normal mock catalogues which reproduce the clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) galaxies. The presented statistical method requires no specific analytical model to construct the likelihood function, and runs with negligible computational cost, after training. We test this new Artificial Neural Network on real BOSS data, finding Ωm=0.309±0.008, which is consistent with standard analysis results.

The evolution of time-dependent Λ and G in multi-fluid Bianchi type-I cosmological models

Abstract In this work, cosmological solutions based on the time-dependent cosmological ( Λ \Lambda ) and Newtonian ( G G ) running “constants” in the Bianchi type-I spacetime are investigated vis-à-vis known cosmological data. The observationally known values of Ω m , Ω r {\Omega }_{{\rm{m}}},{\Omega }_{{\rm{r}}} and Ω Λ {\Omega }_{\Lambda } have been used to solve the Einstein field equations for the model and the resulting behaviours of the physical and dynamical quantities, with particular emphasis on late-time cosmology, are discussed. Our analysis indicates that certain choices of the defining model parameters give results consistent with the observed behaviour of the universe, such as accelerated expansion and an early anisotropy that vanishes at late times.

NECOLA: Toward a Universal Field-level Cosmological Emulator

We train convolutional neural networks to correct the output of fast and approximate N-body simulations at the field level. Our model, Neural Enhanced COLA (NECOLA), takes as input a snapshot generated by the computationally efficient COLA code and corrects the positions of the cold dark matter particles to match the results of full N-body Quijote simulations. We quantify the accuracy of the network using several summary statistics, and find that NECOLA can reproduce the results of the full N-body simulations with subpercent accuracy down to k ≃ 1 hMpc−1. Furthermore, the model that was trained on simulations with a fixed value of the cosmological parameters is also able to correct the output of COLA simulations with different values of Ωm, Ωb, h, n s , σ 8, w, and M ν with very high accuracy: the power spectrum and the cross-correlation coefficients are within ≃1% down to k = 1 hMpc−1. Our results indicate that the correction to the power spectrum from fast/approximate simulations or field-level perturbation theory is rather universal. Our model represents a first step toward the development of a fast field-level emulator to sample not only primordial mode amplitudes and phases, but also the parameter space defined by the values of the cosmological parameters.

Frequency domain electromagnetic and electrical resistivity geophysical investigation of tar sands deposits in the Ijebu Waterside area, Eastern Dahomey Basin, southwestern Nigeria

The use of electromagnetic conductivity and electrical resistivity geophysical techniques has been employed in this study to investigate the occurrence, thickness, and spatial distribution of bitumen deposit around Makun-Omi in the Ijebu Waterside area of southwestern Nigeria. Subsurface apparent conductivity distribution data obtained using Geonic 34-3 equipment along fifteen traverses which sounded from different depths of 7.5, 15, 30 and 60 m at inter-coil separation of 10, 20 and 40 m in vertical and horizontal coupling modes and ground resistivity distribution measurements, obtained using Geopulse Tiger Allied resistivity meter at fourteen Vertical Electrical Sounding (VES) stations, were processed and employed to characterize the subsurface in terms of tar sands distribution. The conductivity and resistivity distribution in the form of a 3D earth model, iso-depth maps, 2D sections generated from the processed conductivity and resistivity data indicate relatively low conductivity <20 mS/m and high resistivity >1300 Ωm values around tar/bitumen impregnated sands which mostly occurred in the southern part of the study area. Clearly defined conductivity and resistivity anomalies which delineate the lateral and vertical occurrence of tar impregnated sands underscore the efficacy of integrating electromagnetic and electrical resistivity geophysical techniques to identify occurrence of economic deposits of tar sands in parts of southwestern Nigeria.

Evolutions and Calibrations of Long Gamma-Ray-burst Luminosity Correlations Revisited

Abstract Luminosity correlations of long gamma-ray bursts (GRBs) are extensively proposed as an effective complementarity to trace the Hubble diagram of the universe at high redshifts, which is of great importance to explore properties of dark energy. Recently, several empirical luminosity correlations have been statistically proposed from GRB observations. However, to treat a GRB as the distance indicator, there are two key issues: the redshift evolution of luminosity correlations and their calibrations. In this paper, we choose the Amati relation, the correlation between the peak spectra energy and the equivalent isotropic energy of GRBs ( E p – E iso ) as an example and find that the current GRB data set implies that there could be a evolution of the luminosity correlation with respect to the redshift. Therefore, we propose an extended Amati relation with two extra redshift-dependent terms to correct the redshift evolution of the GRB relation. Second, we carefully check the reliability of the calibration method using the low-redshift GRB data. Importantly, we find that the low-redshift calibration method does not take whole correlations between Ω m and coefficients into account. Neglecting this correlation information can break the degeneracies and obtain the biased constraint on Ω m , which is very sensitive to values of parameters for the calibration. A small shift in the parameters of the “calibrated” relation could significantly change the final constraint on Ω m in the low-redshift calibration method. Finally, we simulate several GRB samples with different statistical errors and find that, in order to correctly recover the fiducial value of Ω m , using the low-redshift calibration method, we need a large number of GRB samples with high precisions.

Anisotropic expansion and SNIa: An open issue

We review the appropriateness of using SNIa observations to detect potential signatures of anisotropic expansion in the Universe. We focus on Union2 and SNLS3 SNIa datasets and use the hemispherical comparison method to detect possible anisotropic features. Unlike some previous works where non-diagonal elements of the covariance matrix were neglected, we use the full covariance matrix of the SNIa data, thus obtaining more realistic and not underestimated errors. As a matter of fact, the significance of previously claimed detections of a preferred direction in the Union2 dataset completely disappears once we include the effects of using the full covariance matrix. Moreover, we also find that such a preferred direction is aligned with the orthogonal direction of the SDSS observational plane and this suggests a clear indication that the SDSS subsample of the Union2 dataset introduces a significant bias, making the detected preferred direction unphysical. We thus find that current SNIa surveys are inappropriate to test anisotropic features due to their highly non-homogeneous angular distribution in the sky. In addition, after removal of the highest inhomogeneous sub-samples, the number of SNIa is too low. Finally, we take advantage of the particular distribution of SNLS SNIa sub-sample in the SNLS3 data set, in which the observations were taken along four different directions. We fit each direction independently and find consistent results at the 1σ level. Although the likelihoods peak at relatively different values of Ωm, the low number of data along each direction gives rise to large errors so that the likelihoods are sufficiently broad as to overlap within 1σ.

Cosmological constraints from supernova data set with corrected redshift

Observations of distant type Ia supernovae (SNe Ia), used as standard candles, support the notion that the Cosmos is filled with a mysterious form of energy, the dark energy. The constraints on cosmological parameters derived from data of SNe Ia and the measurements of the cosmic microwave background anisotropies indicate that the dark energy amounts to ≈ 70% of all the energy contained in the Universe. In the hypothesis of a flat Universe (Ωm + ΩΛ = 1), we investigate if the dark energy is really required in order to explain the SNe Ia experimental data, and, in this case, how much of such unknown energy is actually deduced from the analysis of these data and must be introduced in the ΛCDM model of cosmology. In particular we are interested in verifying if the Einstein–de Sitter model of the expanding Universe is really to be ruled out. By using a fitting procedure based on the Newton method search for a minimum, we reanalyzed the "Union compilation" reported by Kowalski et al. (2008) formed by 307 SNe, obtaining a very different estimate of the dark energy, that is ≈ 60%. Furthermore, in order to balance the correction of the apparent magnitude of SNe Ia, due to the dilation or stretching of the corresponding light curve width, we introduce a suitable modified redsfhit. Taking into account this correction, we refitted the Union compilation dataset after a selection cut. The main result that emerges from our analysis is that the values of Ωm and ΩΛ strongly depend on the fitting procedure and the selected sample. In particular, the constraint we obtain on the mass density, normalized by the critical mass density, is Ωm = 0.7 for a sample of 252, and Ωm = 1 for a sample of 242 SNe Ia respectively. The latter case does not imply the existence of any additional form of dark energy.

Cosmology with the Planck cluster sample

It has been long recognized that, besides being a formidable experiment to observe the primordial cosmic microwave background (CMB) anisotropies, Planck will also have the capability to detect galaxy clusters via their Sunyaev–Zel'dovich (SZ) imprint. In this paper constraints on cosmological parameters derivable from the Planck cluster candidate sample are examined for the first time as a function of cluster sample selection and purity obtained from realistic simulations of the microwave sky at the Planck observing frequency bands, observation process modelling and a cluster extraction pipeline. In particular, we employ a multifrequency matched filtering (MFMF) method to recover clusters from mock simulations of Planck observations. Obtainable cosmological constraints under realistic assumptions of priors and knowledge about cluster redshifts are discussed. Just relying on cluster redshift abundances without making use of recovered cluster fluxes, it is shown that from the Planck cluster catalogue cosmological constraints comparable to the ones derived from recent primordial CMB power spectrum measurements can be achieved. For example, for a concordance Λ cold dark matter (ΛCDM) model and a redshift binning of Δz= 0.1, the 1σ uncertainties on the values of Ωm and σ8 are ΔΩm≈ 0.031 and Δσ8≈ 0.014, respectively. Furthermore, we find that the constraint of the matter density depends strongly on the prior which can be imposed on the Hubble parameter by other observational means.

Cosmic mimicry: is LCDM a braneworld in disguise?

For a broad range of parameter values, braneworld models display a remarkable property whichwe call cosmic mimicry. Cosmic mimicry is characterized by the fact that, at low redshifts, theHubble parameter in the braneworld model is virtually indistinguishable from that in the LCDM(Λ+cold dark matter) cosmology. An important point to note is that theΩm parameters in the braneworld model and in the LCDM cosmology can neverthelessbe quite different. Thus, at high redshifts (early times), the braneworldasymptotically expands like a matter-dominated universe with the value ofΩm inferred from the observations of the local matter density. At low redshifts(late times), the braneworld model behaves almost exactly like the LCDMmodel but with a renormalized value of the cosmological density parameterΩmLCDM. The valueof ΩmLCDM is smaller(larger) than Ωm in the braneworld model with positive (negative) brane tension. The redshift which characterizescosmic mimicry is related to the parameters in the higher-dimensional braneworldLagrangian. Cosmic mimicry is a natural consequence of the scale dependence of gravity inbraneworld models. The change in the value of the cosmological density parameter (fromΩm athigh z to ΩmLCDM atlow z) is shown to be related to the spatial dependence of the effective gravitational constantGeff in braneworld theory. A subclass of mimicry models lead to an older age of the universeand also predict a redshift of reionization which is lower than in the LCDM cosmology. These models might therefore provide a background cosmologywhich is in better agreement both with the observed quasar abundance at and with the large optical depth to reionization measured by the Wilkinson microwaveanisotropy probe.

On the Absence of Gravitational Lensing of the Cosmic Microwave Background

The magnification of distant sources by mass clumps at lower (z ≤ 1) redshifts is calculated analytically. The clumps are initially assumed to be galaxy group isothermal spheres with properties inferred from an extensive survey. The average effect, which includes strong lensing, is exactly counteracted by the beam divergence in between clumps (more precisely, the average reciprocal magnification cancels the inverse Dyer-Roeder demagnification). This conclusion is independent of the matter density function within each clump, and remains valid for arbitrary values of Ωm and ΩΛ. When tested against the cosmic microwave background data, a rather large lensing-induced dispersion in the angular size of the primary acoustic peaks of the temperature-temperature (TT) power spectrum is inconsistent with WMAP observations. The situation is unchanged by the use of Navarro-Frenk-White (NFW) profiles for the density distribution of groups, which lead in fact to slightly larger fluctuations. Finally, our formulae are applied to an ensemble of NFW mass clumps or isothermal spheres having the properties of galaxy clusters. The acoustic peak size dispersion remains unobservably large and is also excluded by WMAP. For galaxy groups, two possible ways of reconciling with the data are proposed, both exploiting maximally the uncertainties in our knowledge of group properties. The same escape routes are not available in the case of clusters, however, because their properties are well understood. Here we have a more robust conclusion: neither the NFW nor isothermal sphere profiles are accurate descriptions of clusters, or important elements of physics responsible for shaping zero-curvature space are missing from the standard cosmological model. When all the effects are accrued, it is difficult to understand how WMAP could reveal no evidence whatsoever of lensing by groups and clusters.

The Probability Distribution Function of Light in the Universe: Results from Hydrodynamic Simulations

While second and higher order correlations of the light distribution have received extensive study, the lowest order probability distribution function (PDF)—the probability that a unit volume of space will emit a given amount of light—has received very little attention. We estimate this function with the aid of hydrodynamic simulations of the ΛCDM model, finding it significantly different from the mass density PDF, and not simply related to it by linear bias or any of the other prescriptions commonly adopted. If the optical light PDF is, in reality, similar to what we find in the simulations, then some measures of Ωm based on the mass-to-light ratio and the cosmic virial theorem will have significantly underestimated Ωm. Basically, the problem is one of selection bias, with galaxy-forming regions being unrepresentative of the dark matter distribution in a way not described by linear bias. Knowledge of the optical PDF and the plausible assumption of a lognormal distribution for the matter PDF will allow one to correct for these selection biases. We find that this correction (which amounts to 20%-30%) brings the values of Ωm estimated by using the mass-to-light ratio and the cosmic virial theorem to the range Ωm = 0.2-0.3, in better agreement with the Wilkinson Microwave Anisotropy Probe result than the uncorrected estimates. In addition, the relation between mass and light PDFs gives us insight concerning the nature of the void phenomenon. In particular, our simulation indicates that 20% of mass is distributed in voids, which occupy 85% of volume in the universe.

Detecting Topology in a Nearly Flat Hyperbolic Universe

Cosmic microwave background data shows the observable universe to be nearly flat, but leaves open the question of whether it is simply or multiply connected. Several authors have investigated whether the topology of a multiconnected hyperbolic universe would be detectable when 0.9<Ω<1. However, the possibility of detecting a given topology varies depending on the location of the observer within the space. Recent studies have assumed the observer sits at a favorable location. The present paper extends that work to consider observers at all points in the space, and (for given values of Ωm and ΩΛ and a given topology) computes the probability that a randomly placed observer could detect the topology. The computations show that when Ω=0.98 a randomly placed observer has a reasonable chance (~50%) of detecting a hyperbolic topology, but when Ω=0.99 the chances are low (<10%) and decrease still further as Ω approaches one.

Reconstruction Analysis of theIRASPoint Source Catalog Redshift Survey

We present the results of reconstruction analysis of the galaxy distribution in a spherical region of radius 50 h-1 Mpc centered on the Local Group, as mapped by the IRAS Point Source Catalog Redshift Survey (PSCz). We reconstruct this galaxy distribution using 15 different models for structure formation in the universe, each model consisting of a set of assumptions regarding the value of the cosmological mass-density parameter Ωm and the amplitude and nature of the biasing between IRAS galaxies and the underlying mass. For every model, we also reconstruct 10 mock PSCz catalogs derived from the outputs of numerical simulations that have the appropriate values of Ωm and bias. We quantify the accuracy of a reconstruction using a variety of statistics and compare the accuracy of each reconstruction of the PSCz catalog with the accuracy expected based on the mock-catalog reconstructions of the corresponding model. We find that gravitational instability of Gaussian primordial mass-density fluctuations can account for the galaxy distribution in the PSCz catalog, at least for some plausible assumptions about the value of Ωm and the biasing between IRAS galaxies and mass. However, unbiased models in which IRAS galaxies trace mass fail to reconstruct the PSCz catalog accurately, both for Ωm = 0.4 and for Ωm = 1. Low-Ωm models in which IRAS galaxies are antibiased with respect to the mass distribution are the most successful in reconstructing the PSCz catalog. In particular, a model with Ωm = 0.4 and IRAS galaxies related to the mass distribution according to the predictions of a semianalytic galaxy formation model is very successful in reproducing the properties of the PSCz galaxy distribution.

QUINTESSENCE MODEL AND COSMIC MICROWAVE BACKGROUND

A particular kind of quintessence is considered with equation of motion pQ/ρQ = -1, corresponding to a cosmological term with the time-dependece Λ(t) = Λ(t0) (R(t0)/R(t))P and we examine how values of Ωm and ΩΛ depend on P.

Constraints on ΩB, Ωm, andhfrom MAXIMA and BOOMERANG

We analyze the BOOMERANG and MAXIMA results in the context of simplest inflationary universes: ΩTotal = 1, ns 1. We attempt to constrain three other parameters—h, ΩB, and Ωm—from these observations. We show that (1) the data are consistent with the values of Ωm and h inferred from other observations and (2) the value of ΩBh2 is too high to be compatible with big bang nucleosynthesis observations at the 2 σ level for ns = 1. We also include two cosmic background imager (CBI) band powers in our analysis. However, the inclusion of CBI band powers doesn't affect our conclusions.

Luminosity Density Estimation from Redshift Surveys and the Mass Density of the Universe

In most direct estimates of the mass density (visible or dark) of the universe, a central input parameter is the luminosity density of the universe. Here we consider the measurement of this luminosity density from redshift surveys, as a function of the yet undetermined characteristic scale RH at which the spatial distribution of visible matter tends to a well-defined homogeneity. Making the canonical assumption that the cluster mass-to-luminosity ratio / is the universal one, we can estimate the total mass density as a function Ωm(RH, /). Taking the highest estimated cluster value / ≈ 300 h M☉/L☉ and a conservative lower limit RH 20 h-1 Mpc, we obtain the upper bound Ωm 0.1. We note that, for values of the homogeneity scale RH in the range RH ≈ (90 ± 45) h Mpc, the value of Ωm may be compatible with the nucleosynthesis inferred density in baryons.

CMB WITH QUINTESSENCE: ANALYTIC APPROACH AND CMBFAST

A particular kind of quintessence is considered, with equation of motion pQ/ρQ=-1, corresponding to a cosmological term with time-dependence Λ(t)=Λ(t0)(R(t0)/R(t))P which we examine initially for 0≤P<3. Energy conservation is imposed, as is consistency with big-bang nucleosynthesis, and the range of allowed P is thereby much restricted to 0≤P<0.2. The position of the first Doppler peak is computed analytically and the result combined with analysis of high-Z supernovae to find how values of Ωm and ΩΛ depend on P. Some comparison is made to the CMBFAST public code.