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Abstract: A growing neutrino mass can stop the dynamical evolution of a dark energy scalar field, thus explaining the “why now” problem. We show that such models lead to a substantial neutrino clustering on the scales of superclusters. Non-linear neutrino lumps form at redshift and could partially drag the clustering of dark matter. If observed, large scale non-linear structures could be an indication for a new attractive “cosmon force” stronger than gravity. [Copyright &y& Elsevier]

Cosmic shear is one of the primary probes to test gravity with current and future surveys. There are two main techniques to analyse a cosmic shear survey: a tomographic method, where correlations between the lensing signals in different redshift bins are used to recover redshift information, and a 3D approach, where the full redshift information is carried through the entire analysis. Here we compare the two methods, by forecasting cosmological constraints for future surveys like Euclid. We extend the 3D formalism for the first time to theories beyond the standard model, belonging to the Horndeski class. This includes the majority of universally coupled extensions to ΛCDM with one scalar degree of freedom in addition to the metric, still in agreement with current observations. Given a fixed background, the evolution of linear perturbations in Horndeski gravity is described by a set of four functions of time only. We model their time evolution assuming proportionality to the dark energy density fraction and place Fisher matrix constraints on the proportionality coefficients. We find that a 3D analysis can constrain Horndeski theories better than a tomographic one, in particular with a decrease in the errors of the order of 20 $${{\ \rm per\ cent}}$$. This paper shows for the first time a quantitative comparison on an equal footing between Fisher matrix forecasts for both a fully 3D and a tomographic analysis of cosmic shear surveys. The increased sensitivity of the 3D formalism comes from its ability to retain information on the source redshifts along the entire analysis. [ABSTRACT FROM AUTHOR]

Context. The Copernican principle, the notion that we are not at a special location in the Universe, is one of the cornerstones of modern cosmology. Its violation would invalidate the Friedmann-Lemaître-Robertson-Walker metric, causing a major change in our understanding of the Universe. Thus, it is of fundamental importance to perform observational tests of this principle. Aims. We determine the precision with which future surveys will be able to test the Copernican principle and their ability to detect any possible violations. Methods. We forecast constraints on the inhomogeneous Lemaître-Tolman-Bondi (LTB) model with a cosmological constant Λ, basically a cosmological constant Λ and cold dark matter (CDM) model but endowed with a spherical inhomogeneity. We consider combinations of currently available data and simulated Euclid data, together with external data products, based on both ΛCDM and ΛLTB fiducial models. These constraints are compared to the expectations from the Copernican principle. Results. When considering the ΛCDM fiducial model, we find that Euclid data, in combination with other current and forthcoming surveys, will improve the constraints on the Copernican principle by about 30%, with ±10% variations depending on the observables and scales considered. On the other hand, when considering a ΛLTB fiducial model, we find that future Euclid data, combined with other current and forthcoming datasets, will be able to detect gigaparsec-scale inhomogeneities of contrast −0.1. Conclusions. Next-generation surveys, such as Euclid, will thoroughly test homogeneity at large scales, tightening the constraints on possible violations of the Copernican principle. [ABSTRACT FROM AUTHOR]

We consider a model of interacting cosmological constant/quintessence, where dark matter and dark energy behave as, respectively, two coexisting phases of a fluid, a thermally excited Bose component and a condensate, respectively. In a simple phenomenological model for the dark components interaction we find that their energy density evolution is strongly coupled during the universe evolution. This feature provides a possible way out for the coincidence problem affecting many quintessence models. [ABSTRACT FROM AUTHOR]

Context. The data from the Euclid mission will enable the measurement of the angular positions and weak lensing shapes of over a billion galaxies, with their photometric redshifts obtained together with ground-based observations. This large dataset, with well-controlled systematic effects, will allow for cosmological analyses using the angular clustering of galaxies (GCph) and cosmic shear (WL). For Euclid, these two cosmological probes will not be independent because they will probe the same volume of the Universe. The cross-correlation (XC) between these probes can tighten constraints and is therefore important to quantify their impact for Euclid. Aims. In this study, we therefore extend the recently published Euclid forecasts by carefully quantifying the impact of XC not only on the final parameter constraints for different cosmological models, but also on the nuisance parameters. In particular, we aim to decipher the amount of additional information that XC can provide for parameters encoding systematic effects, such as galaxy bias, intrinsic alignments (IAs), and knowledge of the redshift distributions. Methods. We follow the Fisher matrix formalism and make use of previously validated codes. We also investigate a different galaxy bias model, which was obtained from the Flagship simulation, and additional photometric-redshift uncertainties; we also elucidate the impact of including the XC terms on constraining these latter. Results. Starting with a baseline model, we show that the XC terms reduce the uncertainties on galaxy bias by ∼17% and the uncertainties on IA by a factor of about four. The XC terms also help in constraining the γ parameter for minimal modified gravity models. Concerning galaxy bias, we observe that the role of the XC terms on the final parameter constraints is qualitatively the same irrespective of the specific galaxy-bias model used. For IA, we show that the XC terms can help in distinguishing between different models, and that if IA terms are neglected then this can lead to significant biases on the cosmological parameters. Finally, we show that the XC terms can lead to a better determination of the mean of the photometric galaxy distributions. Conclusions. We find that the XC between GCph and WL within the Euclid survey is necessary to extract the full information content from the data in future analyses. These terms help in better constraining the cosmological model, and also lead to a better understanding of the systematic effects that contaminate these probes. Furthermore, we find that XC significantly helps in constraining the mean of the photometric-redshift distributions, but, at the same time, it requires more precise knowledge of this mean with respect to single probes in order not to degrade the final "figure of merit". [ABSTRACT FROM AUTHOR]

Aims. The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. The estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on various individual methodologies and numerical implementations, which were developed for different observational probes and for the combination thereof. In this paper we present validated forecasts, which combine both theoretical and observational ingredients for different cosmological probes. This work is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts. Methods. We describe in detail the methods adopted for Fisher matrix forecasts, which were applied to galaxy clustering, weak lensing, and the combination thereof. We estimated the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations, some of which are made publicly available, in different programming languages, together with a reference training-set of input and output matrices for a set of specific models. These can be used by the reader to validate their own implementations if required. Results. We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setting, for example flat or non-flat spatial cosmologies, or different cuts at non-linear scales. The numerical implementations are now reliable for these settings. We present the results for an optimistic and a pessimistic choice for these types of settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy figure of merit by at least a factor of three. [ABSTRACT FROM AUTHOR]

We present constraints on Horndeski gravity from a combined analysis of cosmic shear, galaxy–galaxy lensing and galaxy clustering from |$450\, \mathrm{deg}^2$| of the Kilo-Degree Survey and the Galaxy And Mass Assembly survey.The Horndeski class of dark energy/modified gravity models includes the majority of universally coupled extensions to ΛCDM with one scalar field in addition to the metric. We study the functions of time that fully describe the evolution of linear perturbations in Horndeski gravity. Our results are compatible throughout with a ΛCDM model. By imposing gravitational wave constraints, we fix the tensor speed excess to zero and consider a subset of models including, e.g. quintessence and f (R) theories. Assuming proportionality of the Horndeski functions αB and αM (kinetic braiding and the Planck mass run rate, respectively) to the dark energy density fraction ΩDE(a) = 1 − Ωm(a), we find for the proportionality coefficients |$\hat{\alpha }_\mathrm{ B} = 0.20_{-0.33}^{+0.20} \,$| and |$\, \hat{\alpha }_\mathrm{ M} = 0.25_{-0.29}^{+0.19}$|⁠. Our value of |$S_8 \equiv \sigma _8 \sqrt{\Omega _{\mathrm{m}}/0.3}$| is in better agreement with the Planck estimate when measured in the enlarged Horndeski parameter space than in a pure ΛCDM scenario. In our joint three-probe analysis, we report a downward shift of the S 8 best-fitting value from the Planck measurement of |$\Delta S_8 = 0.016_{-0.046}^{+0.048}$| in Horndeski gravity, compared to |$\Delta S_8 = 0.059_{-0.039}^{+0.040}$| in ΛCDM. Our constraints are robust to the modelling uncertainty of the non-linear matter power spectrum in Horndeski gravity. Our likelihood code for multiprobe analysis in both ΛCDM and Horndeski gravity is publicly available at https://github.com/alessiospuriomancini/KiDSHorndeski. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the influence of dark energy on structure formation, within five different cosmological models, namely a concordance Λ cold dark matter model, two models with dynamical dark energy, viewed as a quintessence scalar field [using a Ratra and Peebles (RP) and a supergravity (SUGRA) potential form], and two extended quintessence models (EQp and EQn), where the quintessence scalar field interacts non-minimally with gravity (scalar-tensor theories). We adopted for all models the normalization of the matter power spectrum σ8 to match the cosmic microwave background data. In the models with dynamical dark energy and quintessence, we describe the equation of state with w0≈−0.9, still within the range allowed by observations. For each model, we have performed hydrodynamical simulations in a cosmological box of (300 Mpc h−1)3 including baryons and allowing for cooling and star formation. The contemporary presence of evolving dark energy and baryon physics allows us to investigate the interplay between the different background cosmology and the evolution of the luminous matter. Since cluster baryon fraction can be used to constrain other cosmological parameters such as Ωm, we also analyse how dark energy influences the baryon content of galaxy clusters. We find that in models with dynamical dark energy, the evolving cosmological background leads to different star formation rates and different formation histories of galaxy clusters, but the baryon physics is not affected in a relevant way. We investigate several proxies of the cluster mass function based on X-ray observables like temperature, luminosity, Mgas and Ygas. We conclude that the X-ray temperature and Mgas functions are better diagnostic to disentangle the growth of structures among different dark energy models. We also evaluate the cosmological volumes needed to distinguish the dark energy models here investigated using the cluster number counts (in terms of the mass function and the X-ray luminosity and temperature functions). Relaxed, massive clusters, when studied in regions sufficiently far from the centre, are built up in a very similar way despite the different dark energy models here considered. We confirm that the overall baryon fraction is almost independent of the dark energy models at a few per cent level. The same is true for the gas fraction. This evidence reinforces the use of galaxy clusters as cosmological probe of the matter and energy content of the Universe. [ABSTRACT FROM AUTHOR]