Observations Of Baryon Acoustic Oscillations Research Articles

Kernel-, mean-, and noise-marginalized Gaussian processes for exoplanet transits and H0 inference

ABSTRACT Using a fully Bayesian approach, Gaussian process regression is extended to include marginalization over the kernel choice and hyperparameters. In addition, Bayesian model comparison via the evidence enables direct kernel comparison. The calculation of the joint posterior was implemented with a transdimensional sampler which simultaneously samples over the discrete kernel choice and their hyperparameters by embedding these in a higher dimensional space, from which samples are taken using nested sampling. Kernel recovery and mean function inference were explored on synthetic data from exoplanet transit light-curve simulations. Subsequently, the method was extended to marginalization over mean functions and noise models and applied to the inference of the present-day Hubble parameter, H0, from real measurements of the Hubble parameter as a function of redshift, derived from the cosmologically model-independent cosmic chronometer and lambda-cold dark matter-dependent baryon acoustic oscillation observations. The inferred H0 values from the cosmic chronometers, baryon acoustic oscillations, and combined data sets are $H_0= 66 \pm 6,\, 67 \pm 10,\, \mathrm{ and}\,69 \pm 6\,\mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}$, respectively. The kernel posterior of the cosmic chronometers data set prefers a non-stationary linear kernel. Finally, the data sets are shown to be not in tension with ln R = 12.17 ± 0.02.

Minimal model-dependent constraints on cosmological nuisance parameters and cosmic curvature from combinations of cosmological data

The study of cosmic expansion history and the late time cosmic acceleration from observational data depends on the nuisance parameters associated with the data. For example, the absolute peak magnitude of type Ia supernova associated with the type Ia supernova observations and the comoving sound horizon at the baryon drag epoch associated with baryon acoustic oscillation observations are two nuisance parameters. The nuisance parameters associated with the gamma-ray bursts data are also considered. These nuisance parameters are constrained by combining the cosmological observations using the Gaussian process regression method with minimal model dependence. The bounds obtained in this method can be used as the prior for the data analysis while considering the observational data accordingly. Along with these nuisance parameters, the cosmic curvature density parameter is also constrained simultaneously. We find that the constraints on the cosmic curvature density parameter show no significant deviations from a flat Universe.

Model independent bounds on type Ia supernova absolute peak magnitude

We put constraints on the peak absolute magnitude, $M_B$ of type Ia supernova using the Pantheon sample for type Ia supernova observations and the cosmic chronometers data for the Hubble parameter by a model independent and non-parametric approach. Our analysis is based on the Gaussian process regression. We find percent level bounds on the peak absolute magnitude given as $M_B=-19.384\pm0.052$. For completeness and to check the consistency of the results, we also include the Baryon acoustic oscillation data and the prior of the comoving sound horizon from Planck 2018 cosmic microwave background observations. The inclusion of these two data gives tighter constraints on $M_B$ at the sub-percent level. We obtain constraints on $M_B$ from the combination of pantheon compilation of type Ia supernova observations and baryon acoustic oscillation observations given as $M_B=-19.396\pm0.016$. When adding the cosmic chronometer observations with these observations, we find $M_B=-19.395\pm0.015$. The mean values of peak absolute magnitude from all these data are consistent with each other and the values are approximately equal to $-19.4$.

Implications of the singularity theorem for the size of a nonsingular universe

A general property of universes without initial singularity is investigated based on the singularity theorem, assuming the null convergence condition and the global hyperbolicity. As a direct consequence of the singularity theorem, the universal covering of a Cauchy surface of a nonsingular universe with a past trapped surface must have the topology of $S^3$. In addition, we find that the affine size of a nonsingular universe, defined through the affine length of null geodesics, is bounded above. In the case where a part of the nonsingular spacetime is described by Friedmann-Lema\^itre-Robertson-Walker spacetime, we find that this upper bound can be understood as the affine size of the corresponding closed de Sitter universe. We also evaluate the upper bound of the affine size of our Universe based on the trapped surface confirmed by recent observations of baryon acoustic oscillations, assuming that our Universe has no initial singularity.

Observational constraints and dynamical analysis of Kaniadakis horizon-entropy cosmology

ABSTRACT We study the scenario of Kaniadakis horizon-entropy cosmology, which arises from the application of the gravity-thermodynamics conjecture using the Kaniadakis modified entropy. The resulting modified Friedmann equations contain extra terms that constitute an effective dark energy sector. We use data from cosmic chronometers, Type Ia supernova, H ii galaxies, strong lensing systems, and baryon acoustic oscillation observations, and we apply a Bayesian Markov chain Monte Carlo analysis to construct the likelihood contours for the model parameters. We find that the Kaniadakis parameter is constrained around 0, namely around the value where the standard Bekenstein–Hawking is recovered. Concerning the normalized Hubble parameter, we find $h=0.708^{+0.012}_{-0.011}$, a result that is independently verified by applying the $\mathbf {\mathbb {H}}0(z)$ diagnostic and, thus, we conclude that the scenario at hand can alleviate the H0 tension problem. Regarding the transition redshift, the reconstruction of the cosmographic parameters gives $z_{\rm T}=0.715^{+0.042}_{-0.041}$. Furthermore, we apply the Akaike, Bayesian, and deviance information criteria, and we find that in most data sets the scenario is statistical equivalent to Λ cold dark matter one. Moreover, we examine the big bang nucleosynthesis, and we show that the scenario satisfies the corresponding requirements. Additionally, we perform a phase-space analysis, and we show that the Universe past attractor is the matter-dominated epoch, while at late times the Universe results in the dark-energy-dominated solution. Finally, we show that Kaniadakis horizon-entropy cosmology accepts heteroclinic sequences, but it cannot exhibit bounce and turnaround solutions.

Hubble Expansion as an Einstein Curvature

Extending the spacetime manifold of general relativity (GR) to incorporate the Hubble expansion of space as a specific curvature, generates a modified solution with three additional non-zero Christoffel symbols and a reformulated Ricci tensor and curvature. The observational consequences of this reformulation are compared with the ΛCDM model for luminosity distance using the extensive type 1a supernovae (SNe 1a) data with redshift corrected to the CMB, and for angular diameter distance using the recent baryonic acoustic oscillation (BAO) data. For the SNe 1a data, the modified GR and ΛCDM models differ by mag. over zcmb = 0.01 - 1.3, with overall weighted RMS errors of ±0.136μB mag for modified GR and ±0.151μB mag for ΛCDM respectively. The BAO measures span a range z = 0.106 - 2.36, with weighted RMS errors of ±0.034 Mpc with H0 = 67.6 ± 0.25 for the modified GR model, and ±0.085 Mpc with H0 = 70.0 ± 0.25 for the ΛCDM model. The derived GR metric for this new solution describes both the SNe 1a and the BAO observations with comparable accuracy to the w’ΛCDM model. By incorporating the Hubble expansion of space within general relativity as a specific curvature term, these observations may be described without requiring additional parameters for either dark matter or accelerating dark energy.

Most constraining cosmological neutrino mass bounds

We present here up-to-date neutrino mass limits exploiting the most recent cosmological data sets. By making use of the cosmic microwave background temperature fluctuation and polarization measurements, supernovae Ia luminosity distances, baryon acoustic oscillation observations and determinations of the growth rate parameter, we are able to set the most constraining bound to date, $\ensuremath{\sum}{m}_{\ensuremath{\nu}}<0.09\text{ }\text{ }\mathrm{eV}$ at 95% C.L. This very tight limit is obtained without the assumption of any prior on the value of the Hubble constant and highly compromises the viability of the inverted mass ordering as the underlying neutrino mass pattern in nature. The results obtained here further strengthen the case for very large multitracer spectroscopic surveys as unique laboratories for cosmological relics, such as neutrinos: that would be the case of the Dark Energy Spectroscopic Instrument survey and of the Euclid mission.

J-PAS: forecasts on interacting vacuum energy models

The next generation of galaxy surveys will allow us to test some fundamental aspects of the standard cosmological model, including the assumption of a minimal coupling between the components of the dark sector. In this paper, we present the Javalambre Physics of the Accelerated Universe Astrophysical Survey (J-PAS) forecasts on a class of unified models where cold dark matter interacts with a vacuum energy, considering future observations of baryon acoustic oscillations, redshift-space distortions, and the matter power spectrum. After providing a general framework to study the background and linear perturbations, we focus on a concrete interacting model without momentum exchange by taking into account the contribution of baryons. We compare the J-PAS results with those expected for DESI and Euclid surveys and show that J-PAS is competitive to them, especially at low redshifts. Indeed, the predicted errors for the interaction parameter, which measures the departure from a ΛCDM model, can be comparable to the actual errors derived from the current data of cosmic microwave background temperature anisotropies.

Why reducing the cosmic sound horizon alone can not fully resolve the Hubble tension

The mismatch between the locally measured expansion rate of the universe and the one inferred from the cosmic microwave background measurements by Planck in the context of the standard ΛCDM, known as the Hubble tension, has become one of the most pressing problems in cosmology. A large number of amendments to the ΛCDM model have been proposed in order to solve this tension. Many of them introduce new physics, such as early dark energy, modifications of the standard model neutrino sector, extra radiation, primordial magnetic fields or varying fundamental constants, with the aim of reducing the sound horizon at recombination r⋆. We demonstrate here that any model which only reduces r⋆ can never fully resolve the Hubble tension while remaining consistent with other cosmological datasets. We show explicitly that models which achieve a higher Hubble constant with lower values of matter density Ωmh2 run into tension with the observations of baryon acoustic oscillations, while models with larger Ωmh2 develop tension with galaxy weak lensing data.

Probing modified gravity theories with multiple measurements of high-redshift quasars

ABSTRACT In this paper, we quantify the ability of multiple measurements of high-redshift quasars to constrain several theories of modified gravity, including the Dvali–Gabadadze–Porrati braneworld scenario, generalized Chaplygin gas, f(T) modified gravity, and modified polytropic Cardassian model. Recently released sample of 1598 quasars with X-ray and ultraviolet flux measurements in the redshift range of 0.036 ≤ z ≤ 5.1003, as well as a compilation of 120 intermediate-luminosity radio quasars covering the redshift of 0.46 < z < 2.76 are respectively used as standard probes at higher redshifts. For all considered modified gravity theories, our results show that there is still some possibility that the standard Λ cold dark matter (ΛCDM) scenario might not be the best cosmological model preferred by the current quasar observations. In order to improve cosmological constraints, the quasar data are also combined with the latest observations of baryon acoustic oscillations, which strongly complement the constraints. Finally, we discuss the support given by the data to modified gravity theories, applying different information theoretic techniques like the Akaike information criterion, Bayesian information criterion, and Jensen–Shannon divergence.

Probing the seesaw mechanism with cosmological data

We investigate cosmological consequences of an inflationary model which incorporates a generic seesaw extension (types I and II) of the Standard Model of Particle Physics. A non-minimal coupling between the inflaton field and the Ricci scalar is considered as well as radiative corrections at one loop order. This connection between the inflationary dynamics with neutrino physics results in a predictive model whose observational viability is investigated in light of the current cosmic microwave background data, baryon acoustic oscillation observations and type Ia supernovae measurements. Our results show that the non-minimal coupled seesaw potential provides a good description of the observational data when radiative corrections are positive. Such result favours the type II seesaw mechanism over type I and may be an indication for physics beyond the Standard Model.

Does history repeat itself? Periodic Time Cosmology

It has been suggested that the cosmic history might repeat in cycles, with an infinite series of similar aeons in the past and the future. Here, we instead propose that the cosmic history repeats itself exactly, constructing a universe on a periodic temporal history, which we call Periodic Time Cosmology. In particular, the primordial power spectrum, convolved with the transfer function throughout the cosmic history, would form the next aeon's primordial power spectrum. By matching the big bang to the infinite future using a conformal rescaling (a la Penrose), we uniquely determine the primordial power spectrum, in terms of the transfer function up to two free parameters. While nearly scale invariant with a red tilt on large scales, using Planck and Baryonic Acoustic Oscillation observations, we find the minimal model is disfavoured compared to a power-law power spectrum at 5.1σ. However, extensions of ΛCDM cosmic history change the large scale transfer function and can provide better relative fits to the data. For example, the best fit seven parameter model for our Periodic Time Cosmology, with w=−1.024 for dark energy equation of state, is only disfavoured relative to a power-law power spectrum (with the same number of parameters) at 1.8σ level. Therefore, consistency between cosmic history and initial conditions provides a viable description of cosmological observations in the context of Periodic Time Cosmology.

How to Reconstruct a Varying Speed of Light Signal from Baryon Acoustic Oscillations Surveys

We describe an alternative way to use future Baryon Acoustic Oscillation observations to perform non-mainstream research. We focus on the so-called Varying Speed of Light theories, in which the speed of light is made to vary in time. Using prescriptions from future BAO surveys (BOSS, DESI, WFirst-2.4 and SKA), we show that, within such surveys, a 1% Varying Speed of Light (VSL) signal could be detected at 3 sigmas confidence level, in the redshift interval [0.75, 1.45]. Smaller signals will be hardly detected. We also discuss some possible problems related to such kinds of observation, in particular, the degeneracy between a VSL signal and a non-null spatial curvature.

Calibrating effective Ia supernova magnitudes using the distance duality relation

Abstract Using only Ia supernova (SN) observations, it is not possible to distinguish the evolution of the SN absolute magnitude M B from an arbitrary evolution of the Hubble parameter H ( z ) . However, using Etherington’s distance-duality relation, which relates the angular and luminosity distances, together with the observed angular baryon acoustic oscillation (BAO) scale at any redshift z , one may calibrate an effective M B ( z ) . This calibration involves a scale which depends on the cosmological model, however the evolution of the effective M B ( z ) between two redshifts with BAO observations is independent of this scale. The line of sight BAO scale can be used to extend this calibration to redshifts near z . As an application, using BOSS BAO at z = 0.32 and 2.34, JLA supernova at low z and Hubble Space Telescope SN at z > 1.7 , we find a statistically insignificant downward shift M B ( 2.34 ) − M B ( 0.32 ) = − 0.08 ± 0.15 . Replacing BOSS data with the best fit Planck Λ CDM BAO expectations, we find a shift of − 0.24 ± 0.13 . With the SN that will be observed by the James Webb Space Telescope, such a calibration at z = 2.34 will be more precise, and it will serve as an anchor for cosmological analyses with the SN that it will observe at yet higher z .

Constraints on the interacting dark energy with Hubble parameter data and other observational data

We constrain an interacting dark energy model with the Hubble parameter data ( OHD ), as well as the cosmic microwave background ( CMB ) observations from the Planck first data release, the baryonic acoustic oscillation ( BAO ) observations and the type Ia supernovae ( SNe ) data. The model parameters are determined by applying the maximum likelihood method of X 2 fitting by using the Markov Chain Monte Carlo (MCMC) method. The best-fit values of the model parameters with OHD + SNe + CMB + BAO are and Ωm =0.2919-0.0075+0.0075(1σ)-0.0144+0.0151(2σ), wX =-1.0374-0.0452+0.0453(1σ)-0.0886+0.0898(2σ), ξ =3.0976-0.1609+0.1600(1σ)-0.3189+0.3153(2σ), and H0 =69.6479-0.8563+0.8580(1σ)-1.6768+1.6919(2σ). The energy is transferred from dark energy to dark matter. The coincidence problem is slightly alleviated in 1 s range. For comparison, we constrain this model with OHD+BAO+CMB and SNe+CMB + BAO . The results are as follows: (1) It is shown that the OHD can give more stringent constraints on the interacting dark energy model when combined with SNe , CMB and BAO observations, OHD has the potential to alleviate coincidence problem. (2) The special case ( ξ +3 wX , corresponding to the ΛCDM model with no interaction) is within 1 σ confidence level with the OHD + CMB + BAO , SNe + CMB + BAO , and OHD + SNe + CMB + BAO combinations.

Constraining the Generalized and Superfluid Chaplygin Gas Models with the Sandage-Loeb Test**Supported by the National Natural Science Foundation of China under Grants Nos 11175093, 11222545, 11435006, and 11375092, the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 20124306110001, and the K.C. Wong Magna Fund of Ningbo University.

The Sandage-Loeb (SL) test is a direct measurement of the cosmic expansion by probing the redshift drifts of quasi-stellar objects in the ‘redshift desert’ of 2 < z < 5. In this work, we investigate its constraints on the unified dark energy and dark matter models including the generalized Chaplygin gas and the superfluid Chaplygin gas. In addition, type Ia supernovae (SNIa) data and the distance ratios derived from the cosmic microwave background radiation and baryon acoustic oscillation observations (CMB/BAO) are also used. We find that the mock SL data gives the tightest constraints on the model parameters and it can help to reduce the parameter regions allowed by the present SNIa+CMB/BAO by about 75% when all datasets considered are combined. Thus the SL test is a worthy and long awaited measurement to probe effectively the cosmic expanding history and the properties of dark energy.

MODEL-INDEPENDENT EVIDENCE FOR DARK ENERGY EVOLUTION FROM BARYON ACOUSTIC OSCILLATIONS

Baryon Acoustic Oscillations (BAO) allow us to determine the expansion history of the Universe, thereby shedding light on the nature of dark energy. Recent observations of BAO's in the SDSS DR9 and DR11 have provided us with statistically independent measurements of $H(z)$ at redshifts of 0.57 and 2.34, respectively. We show that these measurements can be used to test the cosmological constant hypothesis in a model independent manner by means of an improved version of the $Om$ diagnostic. Our results indicate that the SDSS DR11 measurement of $H(z) = 222 \pm 7$ km/sec/Mpc at $z = 2.34$, when taken in tandem with measurements of $H(z)$ at lower redshifts, imply considerable tension with the standard $\Lambda$CDM model. Our estimation of the new diagnostic $Omh^2$ from SDSS DR9 and DR11 data, namely $Omh^2 \approx 0.122 \pm 0.01$, which is equivalent to $\Omega_{0m}h^2$ for the spatially flat $\Lambda$CDM model, is in tension with the value $\Omega_{0m}h^2 = 0.1426 \pm 0.0025$ determined for $\Lambda$CDM from Planck+WP. This tension is alleviated in models in which the cosmological constant was dynamically screened (compensated) in the past. Such evolving dark energy models display a pole in the effective equation of state of dark energy at high redshifts, which emerges as a smoking gun test for these theories.

Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that the discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard LCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of LCDM model appears to be \approx 3 \sigma\ significant when all cosmological data are used. The model with approximately one additional neutrino type, N_eff \approx 4, and with non-zero total neutrino mass, \approx 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from LCDM model appear mainly due to the usage of recent data on the observations of baryon acoustic oscillations. Larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.

What do we really know about dark energy?

In this paper, we discuss what we truly know about dark energy. I shall argue that, to date, our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, cosmic microwave background anisotropies and observations of baryon acoustic oscillations simply tell us that the observed distance to a given redshift z is larger than the one expected from a Friedmann-Lemaître universe with matter only and the locally measured Hubble parameter.

Latest cosmological constraints on Cardassian expansion models including the updated gamma-ray bursts

We constrain the Cardassian expansion models from the latest observations, including the updated Gamma-ray bursts (GRBs), which are calibrated using a cosmology independent method from the Union2 compilation of type Ia supernovae (SNe Ia). By combining the GRB data with the joint observations from the Union2 SNe Ia set, along with the results from the Cosmic Microwave Background radiation observation from the seven-year Wilkinson Microwave Anisotropy Probe and the baryonic acoustic oscillation observation galaxy sample from the spectroscopic Sloan Digital Sky Survey Data Release, we find significant constraints on the model parameters of the original Cardassian model ΩM0 = 0.282+0.015−0.014, n = 0.03+0.05−0.05; and n = −0.16+0.25−3.26, β = 0.76+0.34−0.58 of the modified polytropic Cardassian model, which are consistent with the ΛCDM model in a 1-σ confidence region. From the reconstruction of the deceleration parameter q(z) in Cardassian models, we obtain the transition redshift zT = 0.73 ± 0.04 for the original Cardassian model and zT = 0.68 ± 0.04 for the modified polytropic Cardassian model.