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Using almost one million galaxies from the final Data Release 12 of the SDSS's Baryon Oscillation Spectroscopic Survey (BOSS), we have obtained, albeit with low significance, a first model-independent determination of the radial baryon acoustic oscillation (BAO) peak with 9 per cent error: Δ z BAO(z eff = 0.51) = 0.0456 ± 0.0042. In order to obtain this measurement, the radial correlation function was computed in 7700 angular pixels, from which the mean correlation function and covariance matrix were obtained, making the analysis completely model-independent. This novel method of obtaining the covariance matrix was validated via comparison with 500 BOSS mock catalogues. This Δ z BAO determination can be used to constrain the background expansion of exotic models for which the assumptions adopted in the standard analysis cannot be satisfied. Future galaxy catalogues from J-PAS, DESI, and Euclid are expected to significantly increase the quality and significance of model-independent determinations of the BAO peak, possibly determined at various redshift and angular positions. We stress that it is imperative to test the standard paradigm in a model-independent way in order to test its foundations, maximize the extraction of information from the data, and look for clues regarding the poorly understood dark energy and dark matter. [ABSTRACT FROM AUTHOR]

The abundances of dark matter haloes in the universe are described by the halo mass function (HMF). It enters most cosmological analyses and parametrizes how the linear growth of primordial perturbations is connected to these abundances. Interestingly, this connection can be made approximately cosmology independent. This made it possible to map in detail its nearuniversal behaviour through large-scale simulations. However, such simulations may suffer from systematic effects, especially if baryonic physics is included. In this paper, we ask how well observations can constrain directly the HMF. The observables we consider are galaxy cluster number counts, galaxy cluster power spectrum and lensing of Type Ia supernovae. Our results show that Dark Energy Survey is capable of putting the first meaningful constraints on the HMF, while both Euclid and J-PAS (Javalambre-Physics of the Accelerated Universe Astrophysical Survey) can give stronger constraints, comparable to the ones from state-ofthe- art simulations. We also find that an independent measurement of cluster masses is even more important for measuring the HMF than for constraining the cosmological parameters, and can vastly improve the determination of the HMF. Measuring the HMF could thus be used to cross-check simulations and their implementation of baryon physics. It could even, if deviations cannot be accounted for, hint at new physics. [ABSTRACT FROM AUTHOR]

We find that if we live at the centre of an inhomogeneity with total density contrast |δ0| ≃ 0.1–0.15, dark energy is not a cosmological constant at 95 per cent confidence level. Observational constraints on the equation of state of dark energy, w, depend strongly on the local matter density around the observer. We model the local inhomogeneity with an exact spherically symmetric solution which features a pressureless matter component and a dark-energy fluid with constant equation of state and negligible sound speed, which reaches a homogeneous solution at finite radius. We fit this model to observations of the local expansion rate, distant supernovae and the cosmic microwave background. We conclude that the possible uncertainty from large-scale structure has to be taken into account if one wants to progress towards not just precision but also accurate cosmology. [ABSTRACT FROM AUTHOR]