An accelerating Universe without Λ\LambdaΛ in concordance with the last H0H_0H0 measured value (original) (raw)
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An Accelerating Universe without Lambda: Delta Gravity Using Monte Carlo †
Universe, 2019
A gravitational field model based on two symmetric tensors, g µν andg µν , is studied, using a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry (δ symmetry). We call themδ matter fields. This theory predicts an accelerating Universe without the need to introduce a cosmological constant Λ by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called C and L 2. With these values, we have fixed all the degrees of freedom in the model. The last H 0 local value measurement is in tension with the CMB Data from Planck. Based on an absolute magnitude M V = −19.23 for the SN, Delta Gravity finds H 0 to be 74.47 ± 1.63 km/(s Mpc). This value is in concordance with the last measurement of the H 0 local value, 73.83 ± 1.48 km/(s Mpc).
Astronomy & astrophysics, 2024
Cosmological observational programs often compare their data not only with Λ cold dark matter (ΛCDM), but also with extensions applying dynamical models of dark energy (DE), whose time-dependent equation of state (EoS) parameters w differ from that of a cosmological constant. We found a degeneracy in the customary computational procedure for the expansion history of cosmological models once dynamical models of DE models were applied. This degeneracy, given the Planck-based Hubble constant H0, provides an infinite number of cosmological models reproducing the Planck-measured cosmic microwave background (CMB) spectrum, including the one with a cosmological constant. Moreover, this degeneracy biases the comparison of ΛCDM with dynamical DE extensions. We present a complementary computational approach, that breaks this degeneracy in the computation of the expansion history of models with a dynamical DE component: the “fixed early densities (EDs)” approach evolves cosmological models from the early Universe to the present, in contrast to the customary “fixed H0” approach, which evolves cosmological models in reverse order. Although there are no equations to determine these EDs from first principles, we find they are accurately approximated by the ΛCDM model. We implemented a refined procedure, applying both approaches, in an amended version of the code CLASS, where we focused on representative dynamical DE models using the Chevallier-Polarski-Linder (CPL) parametrization, studying cases with monotonically increasing and decreasing w over cosmic time. Our results reveal that a dynamical DE model with a decreasing w of the form w(a) = −0.9 + 0.1(1 − a) could provide a resolution to the Hubble tension problem. Moreover, we find that combining the fixed EDs approach and the customary fixed H0 approach, while requesting to yield consistent results and being in agreement with observations across cosmic time, can serve as a kind of consistency check for cosmological models with a dynamical model of DE. Finally, we argue that implementing our proposed consistency check for cosmological models within current Markov chain Monte Carlo (MCMC) methods will increase the accuracy of inferred cosmological parameters significantly, in particular for extensions to ΛCDM. Using our complementary computational scheme, we find characteristic signatures in the late expansion histories of cosmological models, allowing a phenomenological discrimination of DE candidates and a possible resolution to the Hubble tension, by ongoing and future observational programs.
The expansion rate of the intermediate universe in light of Planck
Physics of the Dark Universe, 2014
We use cosmology-independent measurements of the expansion history in the redshift range 0.1 z < 1.2 and compare them with the Cosmic Microwave Background-derived expansion history predictions. The motivation is to investigate if the tension between the local (cosmology independent) Hubble constant H 0 value and the Planck-derived H 0 is also present at other redshifts. We conclude that there is no tension between Planck and cosmology independent-measurements of the Hubble parameter H(z) at 0.1 z < 1.2 for the ΛCDM model (odds of tension are only 1:15, statistically not significant). Considering extensions of the ΛCDM model does not improve these odds (actually makes them worse), thus favouring the simpler model over its extensions. On the other hand the H(z) data are also not in tension with the local H 0 measurements but the combination of all three data-sets shows a highly significant tension (odds ∼ 1 : 400). Thus the new data deepen the mystery of the mismatch between Planck and local H 0 measurements, and cannot univocally determine wether it is an effect localised at a particular redshift. Having said this, we find that assuming the NGC4258 maser distance as the correct anchor for H 0 , brings the odds to comfortable values.
Planck 2013 results. XVI. Cosmological parameters
Astronomy & Astrophysics, 2014
This paper presents the first cosmological results based on Planck measurements of the cosmic microwave background (CMB) temperature and lensing-potential power spectra. We find that the Planck spectra at high multipoles ( > ∼ 40) are extremely well described by the standard spatially-flat six-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations. Within the context of this cosmology, the Planck data determine the cosmological parameters to high precision: the angular size of the sound horizon at recombination, the physical densities of baryons and cold dark matter, and the scalar spectral index are estimated to be θ * = (1.04147±0.00062)×10 −2 , Ω b h 2 = 0.02205±0.00028, Ω c h 2 = 0.1199 ± 0.0027, and n s = 0.9603 ± 0.0073, respectively (68% errors). For this cosmology, we find a low value of the Hubble constant, H 0 = 67.3 ± 1.2 km s −1 Mpc −1 , and a high value of the matter density parameter, Ω m = 0.315 ± 0.017. These values are in tension with recent direct measurements of H 0 and the magnitude-redshift relation for Type Ia supernovae, but are in excellent agreement with geometrical constraints from baryon acoustic oscillation (BAO) surveys. Including curvature, we find that the Universe is consistent with spatial flatness to percent level precision using Planck CMB data alone. We use high-resolution CMB data together with Planck to provide greater control on extragalactic foreground components in an investigation of extensions to the six-parameter ΛCDM model. We present selected results from a large grid of cosmological models, using a range of additional astrophysical data sets in addition to Planck and high-resolution CMB data. None of these models are favoured over the standard six-parameter ΛCDM cosmology. The deviation of the scalar spectral index from unity is insensitive to the addition of tensor modes and to changes in the matter content of the Universe. We find a 95% upper limit of r 0.002 < 0.11 on the tensor-to-scalar ratio. There is no evidence for additional neutrino-like relativistic particles beyond the three families of neutrinos in the standard model. Using BAO and CMB data, we find N eff = 3.30 ± 0.27 for the effective number of relativistic degrees of freedom, and an upper limit of 0.23 eV for the sum of neutrino masses. Our results are in excellent agreement with big bang nucleosynthesis and the standard value of N eff = 3.046. We find no evidence for dynamical dark energy; using BAO and CMB data, the dark energy equation of state parameter is constrained to be w = −1.13 +0.13 −0.10 . We also use the Planck data to set limits on a possible variation of the fine-structure constant, dark matter annihilation and primordial magnetic fields. Despite the success of the six-parameter ΛCDM model in describing the Planck data at high multipoles, we note that this cosmology does not provide a good fit to the temperature power spectrum at low multipoles. The unusual shape of the spectrum in the multipole range 20 < ∼ < ∼ 40 was seen previously in the WMAP data and is a real feature of the primordial CMB anisotropies. The poor fit to the spectrum at low multipoles is not of decisive significance, but is an "anomaly" in an otherwise self-consistent analysis of the Planck temperature data.
An alternative to the cosmological ``concordance model
Astronomy & Astrophysics, 2003
Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat Λ-dominated universe, seeded by nearly scale-invariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einstein-de Sitter universe with zero cosmological constant can fit the data as well as the best concordance model. Moreover unlike a Λ-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect, so is in better agreement with the low quadrupole seen by WMAP. The main problem is that the Hubble constant is required to be rather low: H0 46 km/s/Mpc; we discuss whether this can be consistent with observations. Furthermore for universes consisting only of baryons and cold dark matter, the amplitude of matter fluctuations on cluster scales is too high, a problem which seems generic. However, an additional small contribution (ΩX ∼ 0.1) of matter which does not cluster on small scales, e.g. relic neutrinos with mass of order eV or a 'quintessence' with w ∼ 0, can alleviate this problem. Such models provide a satisfying description of the power spectrum derived from the 2dF galaxy redshift survey and from observations of the Ly-α forest. We conclude that Einstein-de Sitter models can indeed accommodate all data on the large scale structure of the Universe, hence the Hubble diagram of distant Type Ia supernovae remains the only direct evidence for a non-zero cosmological constant.
The Astrophysical Journal, 1996
Recent observations by the Hubble Space Telescope of Cepheids in the Virgo cluster imply a Hubble Constant H 0 = 80 17 km/sec/Mpc. We attempt to clarify some issues of interpretation of these results for determining the global cosmological parameters and . Using the formalism of Bayesian model comparison, the data suggest a universe with a nonzero cosmological constant > 0, but vanishing curvature: + = 1.
Confronting the concordance model of cosmology with Planck data
Journal of Cosmology and Astroparticle Physics, 2014
We confront the concordance (standard) model of cosmology, the spatially flat ΛCDM Universe with power-law form of the primordial spectrum with Planck CMB angular power spectrum data searching for possible smooth deviations beyond the flexibility of the standard model. The departure from the concordance cosmology is modeled in the context of Crossing statistic and statistical significance of this deviation is used as a measure to test the consistency of the standard model to the Planck data. Derived Crossing functions suggest the presence of some broad features in angular spectrum beyond the expectations of the concordance model. Our results indicate that the concordance model of cosmology is consistent to the Planck data only at 2 to 3σ confidence level if we allow smooth deviations from the angular power spectrum given by the concordance model. This might be due to random fluctuations or may hint towards smooth features in the primordial spectrum or departure from another aspect of the standard model. Best fit Crossing functions indicate that there are lack of power in the data at both low-ℓ and high-ℓ with respect to the concordance model. This hints that we may need some modifications in the foreground modeling to resolve the significant inconsistency at high-ℓ. However, presence of some systematics at high-ℓ might be another reason for the deviation we found in our analysis.
Observational Constraints in Delta-gravity: CMB and Supernovae
The Astrophysical Journal, 2021
Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by a new symmetry called . In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them matter fields. This model predicts an accelerating universe without the need to introduce a cosmological constant. In this work, we study the scalar cosmic microwave background (CMB) temperature (TT) power spectrum predicted by DG using an analytical hydrodynamic approach. To fit the Planck satellite’s data with the DG model, we used a Markov Chain Monte Carlo analysis. We also include a study about the compatibility between Type Ia supernovae (SNe Ia) and CMB observations in the DG context. Finally, we obtain the scalar CMB TT power spectrum and the fitted parameters needed to explain both SN Ia data and CMB measurements. The results are in reasonable agreement with both observations considering the analytical approximation. We also discuss...
Physical Review D, 2003
In recent work, we showed that non-perturbative vacuum effects of a very low mass particle could induce, at a redshift of order 1, a transition from a matter-dominated to an accelerating universe. In that work, we used the simplification of a sudden transition out of the matter-dominated stage and were able to fit the Type Ia supernovae (SNe-Ia) data points with a spatially-open universe. In the present work, we find a more accurate, smooth spatially-flat analytic solution to the quantumcorrected Einstein equations. This solution gives a good fit to the SNe-Ia data with a particle mass parameter m h in the range 6.40 × 10 −33 eV to 7.25 × 10 −33 eV. It follows that the ratio of total matter density (including dark matter) to critical density, Ω0, is in the range 0.58 to 0.15, and the age t0 of the universe is in the range 8.10 h −1 Gyr to 12.2 h −1 Gyr, where h is the present value of the Hubble constant, measured as a fraction of the value 100 km/(s Mpc). This spatially-flat model agrees with estimates of the position of the first acoustic peak in the small angular scale fluctuations of the cosmic background radiation, and with light-element abundances of standard big-bang nucleosynthesis. Our model has only a single free parameter, m h , and does not require that we live at a special time in the evolution of the universe.
Galaxies, 2022
The difference from 4 to 6 σ in the Hubble constant (H0) between the values observed with the local (Cepheids and Supernovae Ia, SNe Ia) and the high-z probes (Cosmic Microwave Background obtained by the Planck data) still challenges the astrophysics and cosmology community. Previous analysis has shown that there is an evolution in the Hubble constant that scales as f(z)=H0/(1+z)η, where H0 is H0(z=0) and η is the evolutionary parameter. Here, we investigate if this evolution still holds by using the SNe Ia gathered in the Pantheon sample and the Baryon Acoustic Oscillations. We assume H0=70kms−1Mpc−1 as the local value and divide the Pantheon into three bins ordered in increasing values of redshift. Similar to our previous analysis but varying two cosmological parameters contemporaneously (H0, Ω0m in the ΛCDM model and H0, wa in the w0waCDM model), for each bin we implement a Markov-Chain Monte Carlo analysis (MCMC) obtaining the value of H0 assuming Gaussian priors to restrict the...