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We investigate a recently proposed method for measuring the Hubble constant from gravitational wave detections of binary black hole coalescences without electromagnetic counterparts. In the absence of a direct redshift measurement, the missing information on the left-hand side of the Hubble-Lemaître law is provided by the statistical knowledge on the redshift distribution of sources. We assume that source distribution in redshift depends on unknown hyperparameters, modeling our ignorance of the astrophysical binary black hole distribution. With tens of thousands of these "black sirens"--a realistic figure for the third generation detectors Einstein Telescope and Cosmic Explorer--an observational constraint on the value of the Hubble parameter at percent level can be obtained. This method has the advantage of not relying on electromagnetic counterparts, which accompany a very small fraction of gravitational wave detections, nor on often unavailable or incomplete galaxy catalogs. [ABSTRACT FROM AUTHOR]

Soon the number of type la supernova (SN) measurements should exceed 100 000. Understanding the effect of weak lensing by matter structures on the supernova brightness will then be more important than ever. Although SN lensing is usually seen as a source of systematic noise, we will show that it can be in fact turned into signal. More precisely, the non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitively on the amplitude σ8 of the matter power spectrum. By exploiting this relation, we are able to predict constraints on σ8 of 7% (3%) for a catalog of 100 000 (500 000) SNe of average magnitude error 0.12, without having to assume that such intrinsic dispersion and its redshift evolution are known a priori. The intrinsic dispersion has been assumed to be Gaussian; possible intrinsic non-Gaussianities in the data set (due to the SN themselves and/or to other transients) could be potentially dealt with by means of additional nuisance parameters describing higher moments of the intrinsic dispersion distribution function. This method is independent of and complementary to the standard methods based on cosmic microwave background, cosmic shear, or cluster abundance observables. [ABSTRACT FROM AUTHOR]

A perfect irrotational fluid with the equation of state of dust, irrotational dark matter (IDM), is incapable of virializing and instead forms a cosmoskeleton of filaments with supermassive black holes at the joints. This stark difference from the standard cold dark matter scenario arises because IDM must exhibit potential flow at all times, preventing shell crossing from occurring. This scenario is applicable to general nonoscillating scalar-field theories with a small sound speed. Our model of combined IDM and cold dark matter components thereby provides a solution to the problem of forming the observed billion-solar-mass black holes at redshifts of six and higher. In particular, as a result of the reduced vortical flow, the growth of the black holes is expected to be more rapid at later times as compared to the standard scenario. [ABSTRACT FROM AUTHOR]

With the availability of thousands of type Ia supernovae in the near future the magnitude scatter induced by lensing will become a major issue as it affects parameter estimation. Current N-body simulations are too time consuming to be integrated in the likelihood analyses used for estimating the cosmological parameters. In this paper we show that in the weak-lensing regime a statistical numerical approximation produces accurate results orders of magnitude faster. We write down simple fits to the second, third and fourth central moments of the lensing magnification probability distribution as a function of redshift, of the power spectrum normalization and of the present-day matter density. We also improve upon existing models of lensing variance and show that a shifted log-normal distribution fits well the numerical one. These fits can be easily employed in cosmological likelihood analyses. Moreover, our theoretical predictions make it possible to invert the problem and begin using supernovae lensing to constrain the cosmological parameters. [ABSTRACT FROM AUTHOR]

The halo model (HM) describes the inhomogeneous universe as a collection of halos. The full nonlinear power spectrum of the universe is well approximated by the HM, whose prediction can be easily computed without lengthy numerical simulations. This makes the HM a useful tool in cosmology. Here we explore the lensing properties of the HM by use of the stochastic gravitational lensing method. We obtain for the case of point sources exact and simple integral expressions for the expected value and variance of the lensing convergence, which encode detailed information about the internal halo properties. In particular a wide array of observational biases can be easily incorporated and the dependence of lensing on cosmology is properly taken into account. This simple setup should be useful for a quick calculation of the power spectrum and the related lensing observables, which can play an important role in the extraction of cosmological parameters from, e.g., supernovae observations. Finally, we discuss the probability distribution function of the HM which encodes more information than the first two moments and can more strongly constrain the large-scale structures of the universe. To check the accuracy of our modeling we compare our predictions to the results from the Millennium Simulation. [ABSTRACT FROM AUTHOR]

We revise and extend the stochastic gravitational lensing method (the sGL method) first introduced by Kainulainen and Marra [ Phys. Rev. D 80 123020 (2009)]. Here we include a realistic halo-mass function and density profiles to model the distribution of mass between and within galaxies, galaxy groups, and galaxy clusters. We also introduce a modeling of the filamentary large-scale structures and a method to embed halos into these structures. We show that the sGL method naturally reproduces the weak lensing results for the Millennium simulation. The strength of the sGL method is that a numerical code based on it can compute the lensing probability distribution function (PDF) for a given inhomogeneous model universe in a few seconds. This makes it a useful tool to study how lensing depends on cosmological parameters and its impact on observations. The sGL method can also be used to simulate the effect of a wide array of systematic biases on the observable lensing PDF. As an example we show how simple selection effects may reduce the variance of the observed PDF, which could possibly mask opposite effects from very large-scale structures. We also show how a survey like the Joint Dark Energy Mission could constrain the lensing PDF relative to a given cosmological model. The updated turboGL code is available at turboGL.org. [ABSTRACT FROM AUTHOR]

The mismatch in the value of the Hubble constant from low- and high-redshift observations may be recast as a discrepancy between the low- and high-redshift determinations of the luminosity of Type Ia supernovae, the latter featuring an absolute magnitude which is ≈0.2 mag lower. Here, we propose that a rapid transition in the value of the relative effective gravitational constant μG Geff/GN at zt≃0.01 could explain the lower luminosity (higher magnitude) of local supernovae, thus solving the H0 crisis. In other words, here the tension is solved by featuring a transition at the perturbative rather than background level. A model that features μG=1 for z≲0.01 but μG≃0.9 for z≳0.01 is trivially consistent with local gravitational constraints but would raise the Chandrasekhar mass and so decrease the absolute magnitude of type Ia supernovae at z≳0.01 by the required value of ≈0.2 mag. Such a rapid transition of the effective gravitational constant would not only resolve the Hubble tension but it would also help resolve the growth tension as it would reduce the growth of density perturbations without affecting the Planck/ΛCDM background expansion. [ABSTRACT FROM AUTHOR]

Since there is no known symmetry in nature that prevents a nonminimal coupling between the dark energy (DE) and cold dark matter (CDM) components, such a possibility constitutes an alternative to standard cosmology, with its theoretical and observational consequences being of great interest. In this paper, we propose a new null test on the standard evolution of the dark sector based on the time dependence of the ratio between the CDM and DE energy densities which, in the standard ΛCDM scenario, scales necessarily as a-3. We use the latest measurements of type Ia supernovae, cosmic chronometers and angular baryonic acoustic oscillations to reconstruct the expansion history using model-independent machine learning techniques, namely, the linear model formalism and Gaussian processes. We find that while the standard evolution is consistent with the data at 3σ level, some deviations from the ΛCDM model are found at low redshifts, which may be associated with the current tension between local and global determinations of H0. [ABSTRACT FROM AUTHOR]

The current 3.8σ tension between local [A. G. Riess et al., arXiv:1804.10655.] and global [N. Aghanim et al. (Planck Collaboration), Astron. Astrophys. 596, A107 (2016).] measurements of H0 cannot be fully explained by the concordance ΛCDM model. It could be produced by unknown systematics or by physics beyond the standard model. In particular, nonstandard dark energy models were shown to be able to alleviate this tension. On the other hand, it is well known that linear perturbation theory predicts a cosmic variance on the Hubble parameter H0, which leads to systematic errors on its local determination. Here, we study how including in the likelihood the cosmic variance on H0 affects statistical inference. In particular we consider the γCDM, wCDM and γwCDM parametric extensions of the standard model, which we constrain with the latest CMB, BAO, SNe Ia, RSD and H0 data. We learn two important lessons. First, the systematic error from cosmic variance is--independently of the model--approximately σcv≈0.88 km s-1 Mpc-1 (1.2% H0loc) when considering the redshift range 0.0233≤z≤0.15, which is relative to the main analysis of [A. G. Riess et al., arXiv:1804.10655.], and σcv≈1.5 km s-1 Mpc-1 (2.1% H0loc) when considering the wider redshift range 0.01≤z≤0.15. Although σcv affects the total error budget on local H0, it does not significantly alleviate the tension which remains at ≈3σ. Second, cosmic variance, besides shifting the constraints, can change the results of model selection: much of the statistical advantage of nonstandard models is to alleviate the now-reduced tension. We conclude that, when constraining nonstandard models it is important to include the cosmic variance on H0 if one wants to use the local determination of the Hubble constant by Riess et al. [arXiv:1804.10655]. Doing the contrary could potentially bias the conclusions. [ABSTRACT FROM AUTHOR]

We test both the Friedmann-Lemaître-Robertson-Walker geometry and ΛCDM cosmology in a model-independent way by reconstructing the Hubble function H(z), the comoving distance D(z), and the growth of structure fσ8(z) using the most recent data available. We use the linear model formalism in order to optimally reconstruct the above cosmological functions, together with their derivatives and integrals. We then evaluate four of the null tests available in the literature that probe both background and perturbation assumptions. For all the four tests, we find agreement, within the errors, with the standard cosmological model. [ABSTRACT FROM AUTHOR]

A perfect irrotational fluid with the equation of state of dust, irrotational dark matter (IDM), is incapable of virializing and instead forms a cosmoskeleton of filaments with supermassive black holes at the joints. This stark difference from the standard cold dark matter scenario arises because IDM must exhibit potential flow at all times, preventing shell crossing from occurring. This scenario is applicable to general nonoscillating scalar-field theories with a small sound speed. Our model of combined IDM and cold dark matter components thereby provides a solution to the problem of forming the observed billion-solar-mass black holes at redshifts of six and higher. In particular, as a result of the reduced vortical flow, the growth of the black holes is expected to be more rapid at later times as compared to the standard scenario. [ABSTRACT FROM AUTHOR]

With the availability of thousands of type Ia supernovae in the near future the magnitude scatter induced by lensing will become a major issue as it affects parameter estimation. Current N-body simulations are too time consuming to be integrated in the likelihood analyses used for estimating the cosmological parameters. In this paper we show that in the weak-lensing regime a statistical numerical approximation produces accurate results orders of magnitude faster. We write down simple fits to the second, third and fourth central moments of the lensing magnification probability distribution as a function of redshift, of the power spectrum normalization and of the present-day matter density. We also improve upon existing models of lensing variance and show that a shifted log-normal distribution fits well the numerical one. These fits can be easily employed in cosmological likelihood analyses. Moreover, our theoretical predictions make it possible to invert the problem and begin using supernovae lensing to constrain the cosmological parameters. [ABSTRACT FROM AUTHOR]

Relaxing the conventional assumption of a minimal coupling between the dark matter (DM) and dark energy (DE) fields introduces significant changes in the predicted evolution of the Universe. Therefore, testing such a possibility constitutes an essential task not only for cosmology but also for fundamental physics. In a previous communication [Phys. Rev. D 99, 043521 (2019)], we proposed a new null test for the ΛCDM model based on the time dependence of the ratio between the DM and DE energy densities which is also able to detect potential signatures of interaction between the dark components. In this work, we extend that analysis avoiding the ΛCDM assumption and reconstruct the interaction in the dark sector in a fully model-independent way using data from type Ia supernovae, cosmic chronometers and baryonic acoustic oscillations. According to our analysis, the ΛCDM model is consistent with our model-independent approach at least at 3σ CL over the entire range of redshift studied. On the other hand, our analysis shows that the current background data do not allow us to rule out the existence of an interaction in the dark sector. Finally, we present a forecast for next-generation LSS surveys. In particular, we show that Euclid and SKA will be able to distinguish interacting models with about 4% of precision at z≈1. [ABSTRACT FROM AUTHOR]