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A model with cosmological Bell inequalities: A model with cosmological Bell inequalities
Here, we discuss the possibility of devising cosmological observables which violate Bell's inequalities. Such observables could be used to argue that cosmic scale features were produced by quantum mechanical effects in the very early universe. As evidence of principle, we propose a somewhat elaborate inflationary model where a Bell inequality violating observable can be constructed.
A caveat on building nonlocal models of cosmology
Nonlocal models of cosmology might derive from graviton loop corrections to the effective field equations from the epoch of primordial inflation. Although the Schwinger-Keldysh formalism would automatically produce causal and conserved effective field equations, the models so far proposed have been purely phenomenological. Two techniques have been employed to generate causal and conserved field equations: either varying an invariant nonlocal effective action and then enforcing causality by the ad hoc replacement of any advanced Green's function with its retarded counterpart, or else introducing causal nonlocality into a general ansatz for the field equations and then enforcing conservation. We point out here that the two techniques access very different classes of models, and that neither one of them may represent what would actually arise from fundamental theory.
Cosmological model-independent Gamma-ray bursts calibration and its cosmological constraint to dark energy
As so far, the redshift of Gamma-ray bursts (GRBs) can extend to z ∼ 8 which makes it as a complementary probe of dark energy to supernova Ia (SN Ia). However, the calibration of GRBs is still a big challenge when they are used to constrain cosmological models. Though, the absolute magnitude of GRBs is still unknown, the slopes of GRBs correlations can be used as a useful constraint to dark energy in a completely cosmological model independent way. In this paper, we follow Wang's model-independent distance measurement method and calculate their values by using 109 GRBs events via the so-called Amati relation. Then, we use the obtained model-independent distances to constrain ΛCDM model as an example.
Scaling transformations and the origins of light relics constraints from cosmic microwave background observations
Here, we use here a family of scaling transformations, that scale key rates in the evolution equations, to analytically understand constraints on light relics from cosmic microwave background (CMB) maps, given cosmological models of varying degrees of complexity. We describe the causes of physical effects that are fundamentally important to the constraining power of the data, with a focus on the two that are most novel. We use as a reference model a cosmological model that admits a scaling transformation that increases light relic energy density while avoiding all of these causes. Constraints on light relics in a given model can then be understood as due to the differences between the given model and the reference model, as long as the additional light relics only interact gravitationally with the Standard Model components. This understanding supports the development of cosmological models that can evade light relics constraints from CMB maps.
Crossing statistic: Bayesian interpretation, model selection and resolving dark energy parametrization problem
By introducing Crossing functions and hyper-parameters I show that the Bayesian interpretation of the Crossing Statistics [1] can be used trivially for the purpose of model selection among cosmological models. In this approach to falsify a cosmological model there is no need to compare it with other models or assume any particular form of parametrization for the cosmological quantities like luminosity distance, Hubble parameter or equation of state of dark energy. Instead, hyper-parameters of Crossing functions perform as discriminators between correct and wrong models. Using this approach one can falsify any assumed cosmological model without putting priors on the underlying actual model of the universe and its parameters, hence the issue of dark energy parametrization is resolved. It will be also shown that the sensitivity of the method to the intrinsic dispersion of the data is small that is another important characteristic of the method in testing cosmological models dealing with data with high uncertainties.
Cosmological Evidence Modelling: a new simulation-based approach to constrain cosmology on non-linear scales
Extracting accurate cosmological information from galaxy–galaxy and galaxy–matter correlation functions on non-linear scales (${\lesssim } 10 \, h^{-1}{\rm {Mpc}}$) requires cosmological simulations. Additionally, one has to marginalize over several nuisance parameters of the galaxy–halo connection. However, the computational cost of such simulations prohibits naive implementations of stochastic posterior sampling methods like Markov chain Monte Carlo (MCMC) that would require of order $\mathcal {O}(10^6)$ samples in cosmological parameter space. Several groups have proposed surrogate models as a solution: a so-called emulator is trained to reproduce observables for a limited number of realizations in parameter space. Afterwards, this emulator is used as a surrogate model in an MCMC analysis. In this work, we demonstrate a different method called Cosmological Evidence Modelling (CEM). First, for each simulation, we calculate the Bayesian evidence marginalized over the galaxy–halo connection by repeatedly populating the simulation with galaxies. We show that this Bayesian evidence is directly related to the posterior probability of cosmological parameters. Finally, we build a physically motivated model for how the evidence depends on cosmological parameters as sampled by the simulations. We demonstrate the feasibility of CEM by using simulations from the Aemulus simulation suite and forecasting cosmological constraints from BOSS CMASS measurements of redshift-space distortions. Our analysis includes exploration of how galaxy assembly bias affects cosmological inference. Overall, CEM has several potential advantages over the more common approach of emulating summary statistics, including the ability to easily marginalize over highly complex models of the galaxy–halo connection and greater accuracy, thereby reducing the number of simulations required.
Confronting the concordance model of cosmology with Planck data
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.
The influence of primordial magnetic fields on the spherical collapse model in cosmology
Despite the ever growing observational evidence for the existence of the large scale magnetic fields, their origin and the evolution are not fully understood. If the magnetic fields are of primordial origin, they result in the generation of the secondary matter density perturbations and the previous studies show that such density perturbations enhance the number of dark matter halos. We extend the conventional spherical collapse model by including the Lorentz force which has not been implemented in the previous analysis to study the evolution of density perturbations produced by primordial magnetic fields. The critical over-density δ{sub c} characterizing the halo mass function turns out to be a bigger value, δ{sub c}≅ 1.78, than the conventional one δ{sub c}≅ 1.69 for the perturbations evolved only by the gravitational force. The difference in δ{sub c} between our model and the fully matter dominated cosmological model is small at a low redshift and, hence, only the high mass tail of the mass function is affected by the magnetic fields. At a high redshift, on the other hand, the difference in δ{sub c} becomes large enough to suppress the halo abundance over a wide range of mass scales. The halo abundance is reduced for instance by as large a factor as ∼10{sup 5} at z=9.
Cosmological backreaction within the Szekeres model and emergence of spatial curvature
This paper discusses the phenomenon of backreaction within the Szekeres model. Cosmological backreaction describes how the mean global evolution of the Universe deviates from the Friedmannian evolution. The analysis is based on models of a single cosmological environment and the global ensemble of the Szekeres models (of the Swiss-Cheese-type and Styrofoam-type). The obtained results show that non-linear growth of cosmic structures is associated with the growth of the spatial curvature Ω{sub R} (in the FLRW limit Ω{sub R} → Ω {sub k} ). If averaged over global scales the result depends on the assumed global model of the Universe. Within the Swiss-Cheese model, which does have a fixed background, the volume average follows the evolution of the background, and the global spatial curvature averages out to zero (the background model is the ΛCDM model, which is spatially flat). In the Styrofoam-type model, which does not have a fixed background, the mean evolution deviates from the spatially flat ΛCDM model, and the mean spatial curvature evolves from Ω{sub R} =0 at the CMB to Ω{sub R} ∼ 0.1 at 0 z =. If the Styrofoam-type model correctly captures evolutionary features of the real Universe then one should expect that in our Universe, the spatial curvature should build up (local growth of cosmic structures) and its mean global average should deviate from zero (backreaction). As a result, this paper predicts that the low-redshift Universe should not be spatially flat (i.e. Ω {sub k} ≠ 0, even if in the early Universe Ω {sub k} = 0) and therefore when analysing low- z cosmological data one should keep Ω {sub k} as a free parameter and independent from the CMB constraints.
Spherically symmetric Einstein-aether perfect fluid models
We investigate spherically symmetric cosmological models in Einstein-aether theory with a tilted (non-comoving) perfect fluid source. We use a 1+3 frame formalism and adopt the comoving aether gauge to derive the evolution equations, which form a well-posed system of first order partial differential equations in two variables. We then introduce normalized variables. The formalism is particularly well-suited for numerical computations and the study of the qualitative properties of the models, which are also solutions of Horava gravity. We study the local stability of the equilibrium points of the resulting dynamical system corresponding to physically realistic inhomogeneous cosmological models and astrophysical objects with values for the parameters which are consistent with current constraints. In particular, we consider dust models in (β−) normalized variables and derive a reduced (closed) evolution system and we obtain the general evolution equations for the spatially homogeneous Kantowski-Sachs models using appropriate bounded normalized variables. We then analyse these models, with special emphasis on the future asymptotic behaviour for different values of the parameters. Finally, we investigate static models for a mixture of a (necessarily non-tilted) perfect fluid with a barotropic equations of state and a scalar field.
MORPHOLOGY OF GALAXY CLUSTERS: A COSMOLOGICAL MODEL-INDEPENDENT TEST OF THE COSMIC DISTANCE-DUALITY RELATION
Aiming at comparing different morphological models of galaxy clusters, we use two new methods to make a cosmological model-independent test of the distance-duality (DD) relation. The luminosity distances come from the Union2 compilation of Supernovae Type Ia. The angular diameter distances are given by two cluster models (De Filippis et al. and Bonamente et al.). The advantage of our methods is that they can reduce statistical errors. Concerning the morphological hypotheses for cluster models, it is mainly focused on the comparison between the elliptical {beta}-model and spherical {beta}-model. The spherical {beta}-model is divided into two groups in terms of different reduction methods of angular diameter distances, i.e., the conservative spherical {beta}-model and corrected spherical {beta}-model. Our results show that the DD relation is consistent with the elliptical {beta}-model at 1{sigma} confidence level (CL) for both methods, whereas for almost all spherical {beta}-model parameterizations, the DD relation can only be accommodated at 3{sigma} CL, particularly for the conservative spherical {beta}-model. In order to minimize systematic uncertainties, we also apply the test to the overlap sample, i.e., the same set of clusters modeled by both De Filippis et al. and Bonamente et al. It is found that the DD relation is compatible with the elliptically modeled overlap sample at 1{sigma} CL; however, for most of the parameterizations the DD relation cannot be accommodated even at 3{sigma} CL for any of the two spherical {beta}-models. Therefore, it is reasonable that the marked triaxial ellipsoidal model is a better geometrical hypothesis describing the structure of the galaxy cluster compared with the spherical {beta}-model if the DD relation is valid in cosmological observations.
Observational constraints on modified Chaplygin gas from cosmic growth
We investigate the linear growth function for the large scale structures of the universe considering modified Chaplygin gas as dark energy. Taking into account observational growth data for a given range of redshift from the Wiggle-Z measurements and rms mass fluctuations from Ly-α measurements we numerically analyze cosmological models to constrain the parameters of the MCG. The observational data of Hubble parameter with redshift z is also considered. The Wang-Steinhardt ansatz for growth index γ and growth function f (defined as f = Ω{sub m}{sup γ}(a)) are considered for the numerical analysis. The best-fit values of the equation of state parameters obtained here is employed to study the growth function (f), growth index (γ) and equation of state (ω) with redshift z. The observational constraints on MCG parameters obtained here are compared with that of the GCG model for viable cosmology. It is noted that MCG also satisfactorily accommodates an accelerating phase followed by a matter dominated phase of the universe.
The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological Implications from two Decades of Spectroscopic Surveys at the Apache Point observatory
We present the cosmological implications from final measurements of clustering using galaxies, quasars, and Ly$\alpha$ forests from the completed Sloan Digital Sky Survey (SDSS) lineage of experiments in large-scale structure. These experiments, composed of data from SDSS, SDSS-II, BOSS, and eBOSS, offer independent measurements of baryon acoustic oscillation (BAO) measurements of angular-diameter distances and Hubble distances relative to the sound horizon, $r_d$, from eight different samples and six measurements of the growth rate parameter, $f\sigma_8$, from redshift-space distortions (RSD). This composite sample is the most constraining of its kind and allows us to perform a comprehensive assessment of the cosmological model after two decades of dedicated spectroscopic observation. We show that the BAO data alone are able to rule out dark-energy-free models at more than eight standard deviations in an extension to the flat, $\Lambda$CDM model that allows for curvature. When combined with Planck Cosmic Microwave Background (CMB) measurements of temperature and polarization the BAO data provide nearly an order of magnitude improvement on curvature constraints. The RSD measurements indicate a growth rate that is consistent with predictions from Planck primary data and with General Relativity. When combining the results of SDSS BAO and RSD with external data, all multiple-parameter extensions remain consistent with a $\Lambda$CDM model. Regardless of cosmological model, the precision on $\Omega_\Lambda$, $H_0$, and $\sigma_8$, remains at roughly 1\%, showing changes of less than 0.6\% in the central values between models. The inverse distance ladder measurement under a o$w_0w_a$CDM yields $H_0= 68.20 \pm 0.81 \, \rm km\, s^{-1} Mpc^{-1}$, remaining in tension with several direct determination methods. (abridged)
A Hubble diagram for quasars
We present a new method to test the ΛCDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500 Å flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z∼6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z∼6, which is well matched to that of supernovae in the common z = 0–1.4 redshift interval and extends the test of the cosmological model up to z∼6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a ΛCDM model, we obtain Ω{sub M} = 0.22{sub −0.08}{sup +0.10} and Ω{sub Λ} = 0.92{sub −0.30}{sup +0.18} (Ω{sub M} = 0.28 ± 0.04 and Ω{sub Λ} = 0.73 ± 0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
EFFECT OF MODEL-DEPENDENT COVARIANCE MATRIX FOR STUDYING BARYON ACOUSTIC OSCILLATIONS
Large-scale structures in the universe are a powerful tool to test cosmological models and constrain cosmological parameters. A particular feature of interest comes from baryon acoustic oscillations (BAOs), which are sound waves traveling in the hot plasma of the early universe that stopped at the recombination time. This feature can be observed as a localized bump in the correlation function at the scale of the sound horizon r{sub s} . As such, it provides a standard ruler and a lot of constraining power in the correlation function analysis of galaxy surveys. Moreover, the detection of BAOs at the expected scale gives strong support to cosmological models. Both of these studies (BAO detection and parameter constraints) rely on a statistical modeling of the measured correlation function {xi}-circumflex. Usually {xi}-circumflex is assumed to be Gaussian, with a mean {xi}{sub {theta}} depending on the cosmological model and a covariance matrix C generally approximated as a constant (i.e., independent of the model). In this article, we study whether a realistic model-dependent C {sub {theta}} changes the results of cosmological parameter constraints compared to the approximation of a constant covariance matrix C. For this purpose, we use a new procedure to generate lognormal realizations of the luminous red galaxy sample of the Sloan Digital Sky Survey Data Release 7 to obtain a model-dependent C {sub {theta}} in a reasonable time. The approximation of C {sub {theta}} as a constant creates small changes in the cosmological parameter constraints on our sample. We quantify this modeling error using a lot of simulations and find that it only has a marginal influence on cosmological parameter constraints for current and next-generation galaxy surveys. It can be approximately taken into account by extending the 1{sigma} intervals by a factor Almost-Equal-To 1.3.