Academic literature on the topic 'Beyond-ΛCDM'

We present constraints on extensions to the standard cosmological model of a spatially flat Universe governed by general relativity, a cosmological constant (Λ), and cold dark matter (CDM) by varying the spatial curvature ΩK, the sum of the neutrino masses ∑mν, the dark energy equation of state parameter w, and the Hu-Sawicki f(R) gravity fR0 parameter. With the combined 3 × 2 pt measurements of cosmic shear from the Kilo-Degree Survey (KiDS-1000), galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing from the overlap between KiDS-1000, BOSS, and the spectroscopic 2-degree Field Lensing Survey, we find results that are fully consistent with a flat ΛCDM model with ΩK = 0.011−0.057+0.054, ∑mν < 1.76 eV (95% CL), and w = −0.99−0.13+0.11. The fR0 parameter is unconstrained in our fully non-linear f(R) cosmic shear analysis. Considering three different model selection criteria, we find no clear preference for either the fiducial flat ΛCDM model or any of the considered extensions. In addition to extensions to the flat ΛCDM parameter space, we also explore restrictions to common subsets of the flat ΛCDM parameter space by fixing the amplitude of the primordial power spectrum to the Planck best-fit value, as well as adding external data from supernovae and lensing of the cosmic microwave background (CMB). Neither the beyond-ΛCDM models nor the imposed restrictions explored in this analysis are able to resolve the ∼3σ tension in S8 between the 3 × 2 pt constraints and the Planck temperature and polarisation data, with the exception of wCDM, where the S8 tension is resolved. The tension in the wCDM case persists, however, when considering the joint S8 − w parameter space. The joint flat ΛCDM CMB lensing and 3 × 2 pt analysis is found to yield tight constraints on Ωm = 0.307−0.013+0.008, σ8 = 0.769−0.010+0.022, and S8 = 0.779−0.013+0.013.

ABSTRACT We introduce an emulator approach to predict the non-linear matter power spectrum for broad classes of beyond-ΛCDM cosmologies, using only a suite of ΛCDM N-body simulations. By including a range of suitably modified initial conditions in the simulations, and rescaling the resulting emulator predictions with analytical ‘halo model reactions’, accurate non-linear matter power spectra for general extensions to the standard ΛCDM model can be calculated. We optimize the emulator design by substituting the simulation suite with non-linear predictions from the standard halofit tool. We review the performance of the emulator for artificially generated departures from the standard cosmology as well as for theoretically motivated models, such as f(R) gravity and massive neutrinos. For the majority of cosmologies we have tested, the emulator can reproduce the matter power spectrum with errors ${\lesssim}1{{\ \rm per\ cent}}$ deep into the highly non-linear regime. This work demonstrates that with a well-designed suite of ΛCDM simulations, extensions to the standard cosmological model can be tested in the non-linear regime without any reliance on expensive beyond-ΛCDM simulations.

Abstract We performed a Bayesian study on three beyond ΛCDM phenomenological triggering parameters, the growth index γ, the dark energy equation of state parameter ω and the lensing deviation from the GR prediction parameter Σ, using the latest cosmological geometric, growth and lensing probes, all in a consistent implementation within the modified gravity cosmological solver code MGCLASS. We find, when we combined all our probes, i.e. the cosmic microwave background (CMB), the baryonic acoustic oscilation (BAO), the growth measurements fσ 8 and the 3×2pt joint analysis of weak lensing and galaxy clustering in photometric redshift surveys, assuming flat space, constraints compatible with general relativity and ΛCDM with ω = -1.025 ± 0.045, and Σ = 0.992 ± 0.022 at the 68% level, while γ = 0.633±0.044 is still within ∼ 2σ from the ΛCDM value of γ ∼ 0.55, and that when Σ is considered as constant; while γℓ = -0.025 ±0.045 when the lensing parameter is parameterised as function of a lensing index, introduced for the first time in this work, as Σ(z) = Ωm(z)γℓ .

Abstract We examine the Pantheon supernovae distance data compilation in a model independent analysis to test the validity of cosmic history reconstructions beyond the concordance ΛCDM cosmology. Strong deviations are allowed by the data at z ≳ 1 in the reconstructed Hubble parameter, Om diagnostic, and dark energy equation of state. We explore three interpretations: 1) possibility of the true cosmology being far from ΛCDM, 2) supernovae property evolution, and 3) survey selection effects. The strong (and theoretically problematic) deviations at z ≳ 1 vanish and good consistency with ΛCDM is found with a simple Malmquist-like linear correction. The adjusted data is robust against the model independent iterative smoothing reconstruction. However, we caution that while by eye the original deviation from ΛCDM is striking, χ2 tests do not show the extra linear correction parameter is statistically significant, and a model-independent Gaussian Process regression does not find significant evidence for the need for correction at high-redshifts.

The highly successful standard model of cosmology is built upon two fundamental assumptions: that structure formation proceeds hierarchically through the gravitational collapse of cold dark matter (CDM), and that the late-time expansion of the Universe is dominated by dark energy in the form of the cosmological constant, Λ. While predictions of the ΛCDM model have survived stringent tests spanning a wide range of scales, the true nature of the dark matter and dark energy remains a mystery. Here, we investigate structure formation in well-motivated, alternative scenarios. In the first half, we consider dark matter in the form of sterile neutrinos rather than CDM. We quantify the abundance, formation times and internal structure of sterile neutrino dark matter haloes, before making a detailed comparison of the properties of their substructures compared to their CDM counterparts. Using a semi-analytic model of galaxy formation, we compare observable differences between sterile neutrino and CDM cosmologies and find that future observations of the high redshift Universe and faint dwarf galaxies in the Local Group can place strong constraints on the sterile neutrino scenario. In the second half, the dark matter is assumed to be CDM, but we modify the underlying theory of gravity according to the f(R) model as an alternative theory for accelerated expansion. We test the commonly-assumed quasi-static approximation in f(R) gravity simulations, confirming its validity for a wide choice of model parameters. We then propose a new method for solving the equations of motion in f(R) gravity simulations. Using a suite of high resolution simulations, we find that the new method greatly accelerates the convergence rate of the solutions, improving the efficiency of these simulations by more than a factor of 20 compared to previous methods. This new method will bring us to a new era for precision cosmological tests of gravity.

Le modèle ΛCDM permet de décrire avec une grande précision la plupart des présentes observations cosmologiques. Cependant, l'un de ses paramètres, σ 8, mesurant l'amplitude de fluctuations de la matière, présente une discordance entre sa valeur contrainte par le spectre de puissance angulaire du CMB de la mission Planck, les Cls, et celle déterminée à partir des amas SZ dans l'univers proche. Dans le présent travail on explore divers extensions du modèle ΛCDM comme origines possibles de cette anomalie. Pour tester les effets de ces extensions, nous avons effectué une analyse Monte Carlo on l'on compare les contraintes sur σ 8 à partir de ΛCDM avec celles résultantes de ces extensions, et ceci en utilisant principalement le spectre de puissance CMB seul ou combiné avec des comptages d'amas. Ces derniers sont basés sur différentes relations masse observables et couvrent différents redshift : des amas de rayons X dans l'univers local, des amas de la mission SZ Planck dans l'univers proche ou une estimation des amas détectés par leur richesse photométrique à partir du la future mission Euclid. Du fait qu'une mauvaise détermination de l'étalonnage de la masse des amas pourrait également être la raison de cette divergence, notre approche consistait, lorsqu'on combinait les deux sondes issues des amas et du CMB, à laisser le facteur d'étalonnage libre afin qu'il soit contraint comme les autres paramètres cosmologiques par les deux données. Dans le cas d'introduction de trois neutrinos massifs dégénérés, nous avons trouvé qu'ils n'ont aucun effet significatif sur la correction de l'écart entre les contraintes issues de comptage CMB et ceux issues des Xray ou SZ cluster. Nous avons ensuite permis à l'indice de croissance ƴ de varier. Nous trouvons une corrélation entre ƴ et le paramètre de calibration masse-observable des amas détectés par rayons X qui n'est pas affecté par la présence ou non des neutrinos massifs. [...]
The ΛCDM model has proved successful in describing to a high precision most of nowadays cosmological observations. However, one of its parameters, σ 8, measuring the present matter amplitude fluctuations, constrained from CMB angular power spectrum, the Cls, was found by the Planck mission, in significant tension with value constrained by SZ galaxy cluster counts in the near universe. In the present work we investigate extensions to ΛCDM model as possible origins behind this discrepancy. To test these extensions, we performed a Monte Carlo analysis to compare constraints on σ 8 in ΛCDM with constraints under these extensions, using mainly CMB Cls combined with cluster counts sample. The later were based on different mass observables relations and covered different redshift ranges: X-ray cluster in the local universe, SZ Planck mission clusters from the near universe or photometric richness estimated detected clusters from future high redshift upcoming Euclid alike mission. Because an improper determination of the calibration of cluster mass function could also be behind this discrepancy, our approach was, when combined with CMB, to leave the calibration factor free to vary and be constrained by data. Introducing three degenerate massive neutrinos, we found that they have no significant effect on fixing the discrepancy between CMB and Xray or SZ cluster counts. We then allowed the growth index ƴ to vary. We find a correlation in the confidence space between ƴ and the X-ray mass observable factor not affected by the presence of massive neutrinos, indicating that a modifying gravity is favored over massive neutrinos as a way to alleviate the tension. However, when a SZ cluster sample covering a larger redshift range was used, we found that the correlation between ƴ and the calibration factor, is constrained by the evolution of the growth through redshift and limited to a region where it cannot fix the discrepancy. [...]

Le modèle de concordance actuel, LCDM, a largement réussi à décrire notre Univers. Cependant, des questions cruciales restent sans réponse et deviennent de plus en plus critiques avec la publication continue de données cosmologiques de haute précision. Cela a conduit à l'exploration de modèles LCDM modifiés, parmi lesquels figure le modèle de l'énergie noire couplée, dans lequel les particules de matière noire sont sujettes à une force plus importante que la force gravitationnelle, en raison d'une cinquième force générée par un champ scalaire qui joue le rôle de l'énergie noire. Dans ma thèse, j'introduis une nouvelle paramétrisation du modèle de l'énergie noire couplée où la force de couplage entre les particules de matière noire et le champ scalaire est autorisée à évoluer avec le décalage vers le rouge. Pour sonder un tel modèle de l'énergie noire couplée tomographique, j'utilise des données du fond diffus cosmologique à haut décalage vers le rouge provenant de Planck, ACT et SPT, ainsi qu'une gamme de sondes à bas décalage vers le rouge incluant, pour la première fois, des données de la structure à grande échelle issues de la lentille gravitationnelle faible, de l'agglomération des galaxies, et de leur corrélation croisée. Je constate que les données de la structure à grande échelle nous permettent d'obtenir des contraintes importantes sur le couplage à bas décalages vers le rouge, comparables à celles obtenues avec des données très précises du fonds diffus cosmologique, ce qui en fait une sonde prometteuse pour tester les modèles de l'énergie noire couplée à bas décalages vers le rouge. Je développe ensuite d'autres applications du modèle de l'énergie noire couplée tomographique, comme un modèle de quintessence couplée précoce où le couplage n'est activé que pendant l'ère dominée par le rayonnement, et je contrains un tel modèle phénoménologique avec des données observationnelles pour la première fois. J'explore également des techniques d'apprentissage profond telles que les réseaux neuronaux, pour tester si elles peuvent différencier les données de la structure à grande échelle générées à partir d'un modèle LCDM et d'un modèle de l'énergie noire couplée tomographique. Enfin, nous tournons notre attention vers les relevés actuels de galaxies de stage IV, tels que Euclid, qui réaliseront une cartographie de la structure à grande échelle de l'Univers et fourniront des données de lentille gravitationnelle faible et d'agglomération des galaxies d'une précision sans précédent. Au sein du consortium, je contribue au développement du code de vraisemblance officiel Euclid, avec pour objectif final d'obtenir des contraintes sur les modèles LCDM étendus avec les données Euclid. J'ai également travaillé sur le développement de la chaîne de traitement pour l'inférence à partir de cisaillement cosmique pour UNIONS, un relevé photométrique de galaxies au sol dans l'hémisphère nord qui complétera également les observations Euclid. Ces relevés des structures à grande échelle inaugurent ainsi une ère passionnante de cosmologie de précision, nous permettant d'accroître notre compréhension de l'Univers et de potentiellement découvrir des indices de nouvelles physiques
The current LCDM concordance model has been widely successful in describing our Universe. However, crucial questions remain unanswered and are becoming increasingly critical with the continuous release of high-precision cosmological data. This has led to the exploration of modified LCDM models, one of them being the Coupled Dark Energy (CDE) model, whereby dark matter particles feel a force stronger than gravity, due to the fifth force mediated by a scalar field which plays the role of dark energy. In my thesis, I introduce a new parametrisation of the CDE model where the coupling strength between the dark matter particles and the scalar field is allowed to evolve with redshift. To probe such a tomographic CDE model, I employ high redshift Cosmic Microwave Background (CMB) data from Planck, ACT and SPT, and a range of low redshift probes including, for the first time, Large Scale Structure (LSS) data from weak lensing, galaxy clustering, and their cross-correlation galaxy-galaxy lensing. I find that LSS data allows us to recover tight constraints on coupling at low redshifts, comparable to that obtained with highly precise CMB data, making it a promising probe to test CDE models at low redshifts. I go on to develop other applications of the tomographic CDE model, such as investigations on an early coupled quintessence model whereby coupling is only activated during the radiation-dominated era, and constrain such a phenomenological model with observational data for the first time. I also explore whether deep learning techniques such as neural networks can differentiate between LSS data generated from a LCDM model and a tomographic CDE model. Finally, I turn my attention to current stage IV galaxy surveys such as Euclid, which will map the LSS of the Universe and provide weak lensing and galaxy clustering data of unprecedented accuracy and precision. Within the consortium, I contribute to developing the official Euclid likelihood code, with the ultimate aim of obtaining constraints on extended LCDM models with Euclid data. I have also worked on developing the cosmic shear inference pipeline for UNIONS, a ground-based photometric galaxy survey in the northern hemisphere that will also complement Euclid observations. These LSS surveys thus usher in an exciting era of precision cosmology, allowing us to increase our understanding of the Universe and potentially uncover hints of new physics