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The measurements of the cosmic microwave background (CMB) have played a significant role in understanding the nature of dark energy. In this article, we investigate the dynamics of the dark energy equation of state, utilizing high-precision CMB data from multiple experiments. We begin by examining the Chevallier–Polarski–Linder (CPL) parametrization, a commonly used and recognized framework for describing the dark energy equation of state. We then explore the general Exponential parametrization, which incorporates CPL as its first-order approximation, and extensions of this parametrization that incorporate nonlinear terms. We constrain these scenarios using CMB data from various missions, including the Planck 2018 legacy release, the Wilkinson Microwave Anisotropy Probe (WMAP), the Atacama Cosmology Telescope (ACT), and the South Pole Telescope (SPT), as well as combinations with low-redshift cosmological probes such as Baryon Acoustic Oscillations (BAO) and the Pantheon sample. While the Λ CDM cosmology remains consistent within the 68% confidence level, we observe that the extensions of the CPL parametrization are indistinguishable for Planck data. However, for ACT and SPT data, the inclusion of additional terms begins to reveal a peak in w a,DE that was previously unconstrained. [ABSTRACT FROM AUTHOR]

In this study, we introduce a novel late-time effective dark energy model characterized by a quadratic equation of state (EoS) and rigorously examine its observational constraints. Initially, we delve into the background dynamics of this model, tracing the evolution of fluctuations in linear order. Our approach involves substituting the conventional cosmological constant with a dynamically effective dark energy fluid. Leveraging a diverse array of observational datasets encompassing the Planck 2018 Cosmic Microwave Background (CMB), Type Ia Supernovae (SNe), Baryon Acoustic Oscillations (BAO), and a prior on the Hubble constant H 0 (R21), we constrain the model parameters. We establish the model's consistency by comparing the Hubble parameter as a function of redshift against observational Hubble data (OHD), benchmarking its performance against the Standard Λ CDM model. Additionally, our investigation delves into studies of the model's dynamical behavior by computing cosmological parameters such as the deceleration parameter, relative Hubble parameter, and the evolution of the Hubble rate. Furthermore, employing Bayesian analysis, we determine the Bayesian Evidence for our proposed model compared to the reference Λ CDM model. While our analysis unveils the favorable behavior of the model in various observational tests, the well-known cosmological tensions persist when the full dataset combination is explored. [ABSTRACT FROM AUTHOR]

This research investigates the impact of the nature of Dark Energy (DE) on structure formation, focusing on the matter power spectrum and the Integrated Sachs–Wolfe effect (ISW). By analyzing the matter power spectrum at redshifts z = 0 and z = 5 , as well as the ISW effect on the scale of ℓ = 10 − 100 , the study provides valuable insights into the influence of DE equations of state (EoS) on structure formation. The findings reveal that dynamical DE models exhibit a stronger matter power spectrum compared to constant DE models, with the JBP model demonstrating the highest amplitude and the CPL model the weakest. Additionally, the study delves into the ISW effect, highlighting the time evolution of the ISW source term F (a) and its derivative d F (a) / d a , and demonstrating that models with constant DE EoS exhibit a stronger amplitude of F (a) overall, while dynamical models such as CPL exhibit the highest amplitude among the dynamical models, whereas JBP has the lowest. The study also explores the ISW auto-correlation power spectrum and the ISW cross-correlation power spectrum, revealing that dynamical DE models dominate over those with constant DE EoS across various surveys. Moreover, it emphasizes the potential of studying the non-linear matter power spectrum and incorporating datasets from the small scales to further elucidate the dynamical nature of dark energy. This comprehensive analysis underscores the significance of both the matter power spectrum and the ISW signal in discerning the nature of dark energy, paving the way for future research to explore the matter power spectrum at higher redshifts and in the non-linear regime, providing deeper insights into the dynamical nature of dark energy. [ABSTRACT FROM AUTHOR]

We explore an extension of the standard Λ CDM model by including an interaction between neutrinos and dark matter, and making use of the ground based telescope data of the Cosmic Microwave Background (CMB) from the Atacama Cosmology Telescope (ACT). An indication for a non-zero coupling between dark matter and neutrinos (both assuming a temperature independent and T 2 dependent cross-section) is obtained at the 1 σ level coming from the ACT CMB data alone and when combined with the Planck CMB and Baryon Acoustic Oscillations (BAO) measurements. This result is confirmed by both fixing the effective number of relativistic degrees of freedom in the early Universe to the Standard Model value of N eff = 3. 044 , and allowing N eff to be a free cosmological parameter. Furthermore, when performing a Bayesian model comparison, the interacting ν DM (+ N eff) scenario is mostly preferred over a baseline Λ CDM (+ N eff) cosmology. The preferred value is then used as a benchmark and the potential implications of dark matter's interaction with a sterile neutrino are discussed. [ABSTRACT FROM AUTHOR]

We explore the possible advantages of extending the standard Λ CDM model by more realistic backgrounds compared to its spatially flat Robertson–Walker (RW) spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of Λ CDM, viz., the An- o Λ CDM model. This is to test whether the latest observational data still support spatial flatness and/or isotropic expansion in this case, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the current cosmological tensions associated with Λ CDM. We first present the theoretical background and explicit mathematical construction of An- o Λ CDM; in the simplest manner, combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes, in one Friedmann equation. Then we constrain the parameters of this model and its particular cases, namely, An- Λ CDM, o Λ CDM, and Λ CDM, by using the data sets from different observational probes, viz., Planck cosmic microwave background (CMB) with or without lensing (Lens), baryonic acoustic oscillations (BAO), type Ia Supernovae (SnIa) Pantheon, and cosmic chronometers (CC) data, and discuss the results in detail. Ultimately, we conclude that, within the setup under consideration, (i) the observational data confirm the spatial flatness and isotropic expansion assumptions of Λ CDM, though a very small amount of present-day expansion anisotropy (Ω σ 0) cannot be excluded, e.g., Ω σ 0 ≲ 1 0 − 18 (95% C.L.) for An- Λ CDM from CMB+Lens data, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top Λ CDM does not offer a possible relaxation to the H 0 tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from the CMB data nor does it improve the drastically reduced value of H 0 led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions, even though our findings do not appear to favor the geometric generalizations of Λ CDM considered in this work. [ABSTRACT FROM AUTHOR]

The concordance of the Λ CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter Ω K < 0. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point of view, using measurements of the full-shape (FS) galaxy power spectrum, P (k) , from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By combining Planck data with FS measurements, we break the geometrical degeneracy and find Ω K = 0. 0023 ± 0. 0028. This constrains the Universe to be spatially flat to sub-percent precision, in excellent agreement with results obtained using BAO measurements. However, as with BAO, the overall increase in the best-fit χ 2 suggests a similar level of tension between Planck and P (k) under the assumption of a curved Universe. While the debate on spatial curvature and the concordance between cosmological datasets remains open, our results provide new perspectives on the issue, highlighting the crucial role of FS measurements in the era of precision cosmology. [ABSTRACT FROM AUTHOR]

The Phenomenologically Emergent Dark Energy model, a dark energy model with the same number of free parameters as the flat Λ CDM, has been proposed as a working example of a minimal model which can avoid the current cosmological tensions. A straightforward question is whether or not the inclusion of massive neutrinos and extra relativistic species may spoil such an appealing phenomenological alternative. We present the bounds on M ν and N eff and comment on the long standing H 0 and σ 8 tensions within this cosmological framework with a wealth of cosmological observations. Interestingly, we find, at 95% confidence level, and with the most complete set of cosmological observations, M ν ∼ 0. 2 1 − 0. 14 + 0. 15 eV and N eff = 3. 03 ± 0. 32 i.e. an indication for a non-zero neutrino mass with a significance above 2 σ. The well known Hubble constant tension is considerably easened, with a significance always below the 2 σ level. [ABSTRACT FROM AUTHOR]

We do not solve tensions with concordance cosmology; we do obtain H 0 ≈ 74 km/s/Mpc from CMB+BAO+SN data in our model, but that is not the point. Discrepancies in Hubble constant values obtained by various astrophysical probes should not be viewed in isolation. While one can resolve at least some of the differences through either an early time transition or late time transition in the expansion rate, these introduce other changes. We advocate a holistic approach, using a wide variety of cosmic data, rather than focusing on one number, H 0. Vacuum metamorphosis, a late time transition physically motivated by quantum gravitational effects and with the same number of parameters as Λ CDM, can successfully give a high H 0 value from cosmic microwave background data but fails when combined with multiple distance probes. We also explore the influence of spatial curvature, and of a conjoined analysis of cosmic expansion and growth. [ABSTRACT FROM AUTHOR]

We examine interactions between dark matter and dark energy in light of the latest cosmological observations, focusing on a specific model with coupling proportional to the dark energy density. Our data includes Cosmic Microwave Background (CMB) measurements from the Planck 2018 legacy data release, late-time measurements of the expansion history from Baryon Acoustic Oscillations (BAO) and Supernovae Type Ia (SNeIa), galaxy clustering and cosmic shear measurements from the Dark Energy Survey Year 1 results, and the 2019 local distance ladder measurement of the Hubble constant H 0 from the Hubble Space Telescope. Considering Planck data both in combination with BAO or SNeIa data reduces the H 0 tension to a level which could possibly be compatible with a statistical fluctuation. The very same model also significantly reduces the Ω m − σ 8 tension between CMB and cosmic shear measurements. Interactions between the dark sectors of our Universe remain therefore a promising joint solution to these persisting cosmological tensions. [ABSTRACT FROM AUTHOR]

We consider a quintessence field which transitions from a matter-like to a cosmological constant behaviour between recombination and the present time. We aim at easing the tension in the measurement of the present Hubble rate, and we assess the Λ CDM model properly enlarged to include our quintessence field against cosmological observations. The model does not address the scope we proposed. This result allows us to exclude a class of quintessential models as a solution to the tension in the Hubble constant measurements. [ABSTRACT FROM AUTHOR]