scholarly journals Concordance cosmology?

2020 ◽  
Vol 499 (4) ◽  
pp. 4638-4645
Author(s):  
Youngsoo Park ◽  
Eduardo Rozo
Keyword(s):  
Cold Dark Matter ◽  
Hubble Constant ◽  
Big Bang ◽  
New Physics ◽  
Current Data ◽  
Data Sets ◽  
Late Time ◽  
Acoustic Oscillations ◽  
Dark Energy Survey ◽  
The Difference

ABSTRACT We propose a new intuitive metric for evaluating the tension between two experiments, and apply it to several data sets. While our metric is non-optimal, if evidence of tension is detected, this evidence is robust and easy to interpret. Assuming a flat Lambda cold dark matter (ΛCDM) cosmological model, we find that there is a modest 2.2σ tension between the Dark Energy Survey (DES) Year 1 results and the Planck measurements of the cosmic microwave background. This tension is driven by the difference between the amount of structure observed in the late-time Universe and that predicted from fitting the Planck data, and appears to be unrelated to the tension between Planck and local estimates of the Hubble rate. In particular, combining DES, baryon acoustic oscillations, big bang nucleosynthesis, and supernovae measurements recover a Hubble constant and sound horizon consistent with Planck, and in tension with local distance–ladder measurements. If the tension between these various data sets persists, it is likely that reconciling all current data will require breaking the flat ΛCDM model in at least two different ways: one involving new physics in the early Universe, and one involving new late-time Universe physics.

scholarly journals Determining the Hubble constant without the sound horizon scale: measurements from CMB lensing

2020 ◽  
Vol 501 (2) ◽  
pp. 1823-1835
Author(s):  
Eric J Baxter ◽  
Blake D Sherwin
Keyword(s):  
Power Spectrum ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Hubble Constant ◽  
New Physics ◽  
Data Sets ◽  
Density Parameter ◽  
Acoustic Oscillations ◽  
The Galaxy ◽  
Local Measurements

ABSTRACT Measurements of the Hubble constant, H0, from the cosmic distance ladder are currently in tension with the value inferred from Planck observations of the cosmic microwave background (CMB) and other high-redshift data sets if a flat Λ cold dark matter (ΛCDM) cosmological model is assumed. One of the few promising theoretical resolutions of this tension is to invoke new physics that changes the sound horizon scale in the early Universe; this can bring CMB and baryon acoustic oscillations (BAO) constraints on H0 into better agreement with local measurements. In this paper, we discuss how a measurement of the Hubble constant can be made from the CMB without using information from the sound horizon scale, rs. In particular, we show how measurements of the CMB lensing power spectrum can place interesting constraints on H0 when combined with measurements of either supernovae or galaxy weak lensing, which constrain the matter density parameter. The constraints arise from the sensitivity of the CMB lensing power spectrum to the horizon scale at matter–radiation equality (in projection); this scale could have a different dependence on new physics than the sound horizon. From an analysis of current CMB lensing data from Planck and Pantheon supernovae with conservative external priors, we derive an rs-independent constraint of $H_0 = 73.5\pm 5.3\, {\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$. Forecasts for future CMB surveys indicate that improving constraints beyond an error of $\sigma (H_0) = 3\, {\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$ will be difficult with CMB lensing, although applying similar methods to the galaxy power spectrum may allow for further improvements.

scholarly journals Resolving Hubble tension with the Milne model

2020 ◽  
Vol 29 (14) ◽  
pp. 2043025
Author(s):  
Ram Gopal Vishwakarma
Keyword(s):  
Hubble Constant ◽  
Big Bang ◽  
New Physics ◽  
Late Time ◽  
Standard Cosmology ◽  
Evolution Dynamics ◽  
Age Of The Universe ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

The recent measurements of the Hubble constant based on the standard [Formula: see text]CDM cosmology reveal an underlying disagreement between the early-Universe estimates and the late-time measurements. Moreover, as these measurements improve, the discrepancy not only persists but becomes even more significant and harder to ignore. The present situation places the standard cosmology in jeopardy and provides a tantalizing hint that the problem results from some new physics beyond the [Formula: see text]CDM model. It is shown that a nonconventional theory — the Milne model — which introduces a different evolution dynamics for the Universe, alleviates the Hubble tension significantly. Moreover, the model also averts some long-standing problems of the standard cosmology, for instance, the problems related with the cosmological constant, the horizon, the flatness, the Big Bang singularity, the age of the Universe and the nonconservation of energy.

scholarly journals Cosmic dissonance: are new physics or systematics behind a short sound horizon?

2020 ◽  
Vol 639 ◽  
pp. A57 ◽  
Author(s):  
Nikki Arendse ◽  
Radosław J. Wojtak ◽  
Adriano Agnello ◽  
Geoff C.-F. Chen ◽  
Christopher D. Fassnacht ◽  
...  
Keyword(s):  
Time Delay ◽  
Gravitational Lensing ◽  
Background Radiation ◽  
Hubble Constant ◽  
New Physics ◽  
Physical Models ◽  
Late Time ◽  
Absolute Distance ◽  
Acoustic Oscillations ◽  
Distance Indicators

Context. Persistent tension between low-redshift observations and the cosmic microwave background radiation (CMB), in terms of two fundamental distance scales set by the sound horizon rd and the Hubble constant H0, suggests new physics beyond the Standard Model, departures from concordance cosmology, or residual systematics. Aims. The role of different probe combinations must be assessed, as well as of different physical models that can alter the expansion history of the Universe and the inferred cosmological parameters. Methods. We examined recently updated distance calibrations from Cepheids, gravitational lensing time-delay observations, and the tip of the red giant branch. Calibrating the baryon acoustic oscillations and type Ia supernovae with combinations of the distance indicators, we obtained a joint and self-consistent measurement of H0 and rd at low redshift, independent of cosmological models and CMB inference. In an attempt to alleviate the tension between late-time and CMB-based measurements, we considered four extensions of the standard ΛCDM model. Results. The sound horizon from our different measurements is rd = (137 ± 3stat. ± 2syst.) Mpc based on absolute distance calibration from gravitational lensing and the cosmic distance ladder. Depending on the adopted distance indicators, the combined tension in H0 and rd ranges between 2.3 and 5.1 σ, and it is independent of changes to the low-redshift expansion history. We find that modifications of ΛCDM that change the physics after recombination fail to provide a solution to the problem, for the reason that they only resolve the tension in H0, while the tension in rd remains unchanged. Pre-recombination extensions (with early dark energy or the effective number of neutrinos Neff = 3.24 ± 0.16) are allowed by the data, unless the calibration from Cepheids is included. Conclusions. Results from time-delay lenses are consistent with those from distance-ladder calibrations and point to a discrepancy between absolute distance scales measured from the CMB (assuming the standard cosmological model) and late-time observations. New proposals to resolve this tension should be examined with respect to reconciling not only the Hubble constant but also the sound horizon derived from the CMB and other cosmological probes.

scholarly journals Testing the warmness of dark matter

2019 ◽  
Vol 490 (1) ◽  
pp. 1406-1414 ◽  
Author(s):  
Suresh Kumar ◽  
Rafael C Nunes ◽  
Santosh Kumar Yadav
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Mass Scale ◽  
Acoustic Oscillations ◽  
Microwave Background ◽  
Mean Values ◽  
Λcdm Model ◽  
Cosmological Data

ABSTRACT Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard Λ cold dark matter (ΛCDM) model to the astrophysical and cosmological data. In this paper, we investigate two extended properties of DM: a possible time dependence of the equation of state of DM via Chevallier–Polarski–Linder parametrization, wdm = wdm0 + wdm1(1 − a), and the constant non-null sound speed $\hat{c}^2_{\rm s,dm}$. We analyse these DM properties on top of the base ΛCDM model by using the data from Planck cosmic microwave background (CMB) temperature and polarization anisotropy, baryonic acoustic oscillations (BAOs), and the local value of the Hubble constant from the Hubble Space Telescope (HST). We find new and robust constraints on the extended free parameters of DM. The most tight constraints are imposed by CMB+BAO data, where the three parameters wdm0, wdm1, and $\hat{c}^2_{\rm s,dm}$ are, respectively, constrained to be less than 1.43 × 10−3, 1.44 × 10−3, and 1.79 × 10−6 at 95 per cent CL. All the extended parameters of DM show consistency with zero at 95 per cent CL, indicating no evidence beyond the CDM paradigm. We notice that the extended properties of DM significantly affect several parameters of the base ΛCDM model. In particular, in all the analyses performed here, we find significantly larger mean values of H0 and lower mean values of σ8 in comparison to the base ΛCDM model. Thus, the well-known H0 and σ8 tensions might be reconciled in the presence of extended DM parameters within the ΛCDM framework. Also, we estimate the warmness of DM particles as well as its mass scale, and find a lower bound: ∼500 eV from our analyses.

scholarly journals Dark Energy Survey Year 1 results: measurement of the baryon acoustic oscillation scale in the distribution of galaxies to redshift 1

2018 ◽  
Vol 483 (4) ◽  
pp. 4866-4883 ◽  
Author(s):  
T M C Abbott ◽  
F B Abdalla ◽  
A Alarcon ◽  
S Allam ◽  
F Andrade-Oliveira ◽  
...  
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Angular Diameter ◽  
Acoustic Oscillations ◽  
Distance Measurements ◽  
Angular Diameter Distance ◽  
Dark Energy Survey ◽  
Trade Offs ◽  
Physical Scale ◽  
Energy Survey

ABSTRACT We present angular diameter distance measurements obtained by locating the baryon acoustic oscillations (BAO) scale in the distribution of galaxies selected from the first year of Dark Energy Survey data. We consider a sample of over 1.3 million galaxies distributed over a footprint of 1336 deg2 with 0.6 < $z$photo < 1 and a typical redshift uncertainty of 0.03(1 + $z$). This sample was selected, as fully described in a companion paper, using a colour/magnitude selection that optimizes trade-offs between number density and redshift uncertainty. We investigate the BAO signal in the projected clustering using three conventions, the angular separation, the comoving transverse separation, and spherical harmonics. Further, we compare results obtained from template-based and machine-learning photometric redshift determinations. We use 1800 simulations that approximate our sample in order to produce covariance matrices and allow us to validate our distance scale measurement methodology. We measure the angular diameter distance, DA, at the effective redshift of our sample divided by the true physical scale of the BAO feature, rd. We obtain close to a 4 per cent distance measurement of DA($z$eff = 0.81)/rd = 10.75 ± 0.43. These results are consistent with the flat Λ cold dark matter concordance cosmological model supported by numerous other recent experimental results.

scholarly journals Optimizing galaxy samples for clustering measurements in photometric surveys

2019 ◽  
Vol 491 (3) ◽  
pp. 3535-3552 ◽  
Author(s):  
Dimitrios Tanoglidis ◽  
Chihway Chang ◽  
Joshua Frieman
Keyword(s):  
Cold Dark Matter ◽  
Sample Selection ◽  
Gaussian Model ◽  
Small Subset ◽  
Data Sets ◽  
Trade Off ◽  
Cosmological Constraints ◽  
Dark Energy Survey ◽  
Galaxy Sample ◽  
Cross Correlations

ABSTRACT When analysing galaxy clustering in multiband imaging surveys, there is a trade-off between selecting the largest galaxy samples (to minimize the shot noise) and selecting samples with the best photometric redshift (photo-z) precision, which generally includes only a small subset of galaxies. In this paper, we systematically explore this trade-off. Our analysis is targeted towards the third-year data of the Dark Energy Survey (DES), but our methods hold generally for other data sets. Using a simple Gaussian model for the redshift uncertainties, we carry out a Fisher matrix forecast for cosmological constraints from angular clustering in the redshift range z = 0.2–0.95. We quantify the cosmological constraints using a figure of merit (FoM) that measures the combined constraints on Ωm and σ8 in the context of Λ cold dark matter (ΛCDM) cosmology. We find that the trade-off between sample size and photo-z precision is sensitive to (1) whether cross-correlations between redshift bins are included or not, and (2) the ratio of the redshift bin width δz to the photo-z precision σz. When cross-correlations are included and the redshift bin width is allowed to vary, the highest FoM is achieved when δz ∼ σz. We find that for the typical case of 5−10 redshift bins, optimal results are reached when we use larger, less precise photo-z samples, provided that we include cross-correlations. For samples with higher σz, the overlap between redshift bins is larger, leading to higher cross-correlation amplitudes. This leads to the self-calibration of the photo-z parameters and therefore tighter cosmological constraints. These results can be used to help guide galaxy sample selection for clustering analysis in ongoing and future photometric surveys.

scholarly journals The observed discordances in cosmology signaling new Physics

2020 ◽  
Author(s):  
Haichao Zhang
Keyword(s):  
Cold Dark Matter ◽  
New Physics ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Absolute Mass ◽  
Cold Dark Matter Model ◽  
Matter Model ◽  
Dark Matter Model ◽  
Measured Mass ◽  
Cosmic Model

Abstract The measured values for the cosmic expansion rate, the cosmic radius, the cosmic age, etc. vary with a direct or an indirect methodology. These discrepancies known as the cosmological crisis imply the existence of a new physical field. The coupling of matter to the field causes the ratio between a being measured mass of matter and a reference mass to vary with the field. Any experiment can only measure the relative ratio rather than the absolute mass of matter. Apparently, there are two representations in describing the field dependence of the ratio: the reference (being measured) mass varies with the field while the being measured (reference) mass does not. Therefore, the measured value of every quantity depends on the choice of the representations. A representation is selected based on the conscious or unconscious assumptions in an experiment. This new field can resolve the discrepancies as well as drive the late-time cosmic acceleration. The new closed cosmic model here can remove the tensions in the standard cold dark matter model with Λ being the cosmological constant.

scholarly journals Tempeature Redshift of Photons

2020 ◽  
Author(s):  
Xiaoping Hu
Keyword(s):  
Dark Matter ◽  
Hubble Constant ◽  
Big Bang ◽  
New Physics ◽  
Current Theory ◽  
Big Bang Theory ◽  
Celestial Bodies ◽  
Expansion Force ◽  
The Big Bang ◽  
The Universe

This article presents a new theory on redshift of light from celestial bodies. Lately it has been found that the Hubble constant calculated from different methods discord so much that calls arise for new physics to explain. Also, in addition to many unsolved puzzles like dark matter and source of expansion force, we shall show in this article that the current theory of redshift implies a few hidden, unreasonale assumptions. By assuming photon has temperature and its thermal energy is fully converted to wave energy, this article shows that photon can have a new redshift called Temperature Redshift, which not only is more significant for remote stars or galaxies, but also better fits the observational data, including those used in Hubble constant calculation. As such, if true, this new theory not only adds to our new understanding of photons, but may totally change our current understanding of the Universe, i.e., the Big Bang theory.

scholarly journals A combined analysis of the H0 late time direct measurements and the impact on the Dark Energy sector

2021 ◽  
Vol 502 (2) ◽  
pp. 2065-2073
Author(s):  
Eleonora Di Valentino
Keyword(s):  
Dark Energy ◽  
Time Delay ◽  
Surface Brightness ◽  
Hubble Constant ◽  
New Physics ◽  
Late Time ◽  
Direct Measurements ◽  
Phantom Dark Energy ◽  
Surface Brightness Fluctuations ◽  
The Impact

ABSTRACT We combine 23 Hubble constant measurements based on Cepheids-SN Ia, TRGB-SN Ia, Miras-SN Ia, Masers, Tully Fisher, Surface Brightness Fluctuations, SN II, Time-delay Lensing, Standard Sirens and γ-ray Attenuation, obtaining our best optimistic H0 estimate, that is H0 = 72.94 ± 0.75 km s–1 Mpc–1 at 68 per cent CL. This is in 5.9σ tension with the ΛCDM model, therefore we evaluate its impact on the extended Dark Energy cosmological models that can alleviate the tension. We find more than 4.9σ evidence for a phantom Dark Energy equation of state in the wCDM scenario, the cosmological constant ruled out at more than 3σ in a w0waCDM model and more than 5.7σ evidence for a coupling between Dark Matter and Dark Energy in the IDE scenario. Finally, we check the robustness of our results; and we quote two additional combinations of the Hubble constant. The ultra-conservative estimate, H0 = 72.7 ± 1.1 km s–1 Mpc–1 at 68 per cent CL, is obtained removing the Cepheids-SN Ia and the Time-Delay Lensing based measurements, and confirms the evidence for new physics.

scholarly journals H0LiCOW – XIII. A 2.4 per cent measurement of H0 from lensed quasars: 5.3σ tension between early- and late-Universe probes

2019 ◽  
Vol 498 (1) ◽  
pp. 1420-1439 ◽  
Author(s):  
Kenneth C Wong ◽  
Sherry H Suyu ◽  
Geoff C-F Chen ◽  
Cristian E Rusu ◽  
Martin Millon ◽  
...  
Keyword(s):  
Time Delay ◽  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Joint Analysis ◽  
Type Ia Supernovae ◽  
Acoustic Oscillations ◽  
Type Ia ◽  
Measured Time ◽  
Ia Supernovae

ABSTRACT We present a measurement of the Hubble constant (H0) and other cosmological parameters from a joint analysis of six gravitationally lensed quasars with measured time delays. All lenses except the first are analysed blindly with respect to the cosmological parameters. In a flat Λ cold dark matter (ΛCDM) cosmology, we find $H_{0} = 73.3_{-1.8}^{+1.7}~\mathrm{km~s^{-1}~Mpc^{-1}}$, a $2.4{{\ \rm per\ cent}}$ precision measurement, in agreement with local measurements of H0 from type Ia supernovae calibrated by the distance ladder, but in 3.1σ tension with Planck observations of the cosmic microwave background (CMB). This method is completely independent of both the supernovae and CMB analyses. A combination of time-delay cosmography and the distance ladder results is in 5.3σ tension with Planck CMB determinations of H0 in flat ΛCDM. We compute Bayes factors to verify that all lenses give statistically consistent results, showing that we are not underestimating our uncertainties and are able to control our systematics. We explore extensions to flat ΛCDM using constraints from time-delay cosmography alone, as well as combinations with other cosmological probes, including CMB observations from Planck, baryon acoustic oscillations, and type Ia supernovae. Time-delay cosmography improves the precision of the other probes, demonstrating the strong complementarity. Allowing for spatial curvature does not resolve the tension with Planck. Using the distance constraints from time-delay cosmography to anchor the type Ia supernova distance scale, we reduce the sensitivity of our H0 inference to cosmological model assumptions. For six different cosmological models, our combined inference on H0 ranges from ∼73 to 78 km s−1 Mpc−1, which is consistent with the local distance ladder constraints.

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