CO measurements of z~1-4 galaxies have found that their baryonic gas fractions are significantly higher than galaxies at z=0, with values ranging from 20-80 %. Here, we suggest that the gas fractions inferred from observations of star-forming galaxies at high-z are overestimated, owing to the adoption of locally-calibrated CO-H2 conversion factors (Xco). Evidence from both observations and numerical models suggest that Xco varies smoothly with the physical properties of galaxies, and that Xco can be parameterised simply as a function of both gas phase metallicity and observed CO surface brightness. When applying this functional form, we find fgas ~10-40 % in galaxies with M*=10^10-10^12 Msun at high-z. Moreover, the scatter in the observed fgas-M* relation is lowered by a factor of two. The lower inferred gas fractions arise physically because the interstellar media of high-z galaxies have higher velocity dispersions and gas temperatures than their local counterparts, which results in an Xco that is lower than the z=0 value for both quiescent discs and starbursts. We further compare these gas fractions to those predicted by cosmological galaxy formation models. We show that while the canonically inferred gas fractions from observations are a factor of 2-3 larger at a given stellar mass than predicted by models, our rederived Xco values for z=1-4 galaxies results in revised gas fractions that agree significantly better with the simulations.
JWST high redshift galaxy observations predict a higher star formation efficiency than the standard cosmology does, which poses a new tension to $Λ$CDM. We find that the situation is worse than expected. The true situation is that the Planck CMB measurement has a strong tension with JWST high redshift galaxy observations. Specifically, we make a trial to alleviate this tension by considering alternative cosmological models including dark matter-baryon interaction, $f(R)$ gravity and dynamical dark energy. Within current cosmological constraints from Planck-2018 CMB data, we find that these mod…
With the recent increase in precision of our cosmological datasets, measurements of $Λ$CDM model parameter provided by high- and low-redshift observations started to be in tension, i.e., the obtained values of such parameters were shown to be significantly different in a statistical sense. In~this work we tackle the tension on the value of the Hubble parameter, $H_0$, and the weighted amplitude of matter fluctuations, $S_8$, obtained from local or low-redshift measurements and from cosmic microwave background (CMB) observations. We combine the main approaches previously used in the literature …
In this work, we study the cosmological constant problem and Hubble tension in the void-dominated cosmology scenario \cite{Yusofi:2022hgg}. For this goal, we will first consider the cosmic voids in the cosmic web as interconnected ideal spherical bubbles at the early Planck scale and late large scale. By heuristic calculations for each cosmic void, we obtain particular mass density and cosmological constant that are the same order of magnitude as the entire universe on any scale. The values obtained for the cosmological constant vary from scale to scale. As a result, it will be shown that ther…
The abundance of clusters is a classical cosmological probe sensitive to both the geometrical aspects and the growth rate of structures. The abundance of clusters of galaxies measured by Planck has been found to be in tension with the prediction of the LCDM models normalized to Planck CMB fluctuations power spectra. The same tension appears with X-ray cluster local abundance. Massive neutrinos and modified gravity are two possible solutions to fix this tension. Alternatively, others options include a bias in the selection procedure or in the mass calibration of clusters. We present a study, ba…
Current cosmological observations point to a serious discrepancy between the observed Hubble parameter obtained using direct and cosmic microwave background radiation (CMBR) measurements. Besides this, the so called Hubble--Lemaître tension, we also find considerable evidence in diverse cosmological observables that indicate violation of the cosmological principle. In this paper, we suggest that both these discrepancies are related and can be explained by invoking superhorizon perturbations in the Universe. We implement this by considering a single superhorizon mode and showing that it leads t…
Although cosmic microwave background (CMB) is the most powerful cosmological probe of neutrino masses, it is in trouble with local direct measurements of $H_0$, which is called the $H_0$ tension. Since neutrino masses are correlated with $H_0$ in CMB, one can expect the cosmological bound on neutrino masses would be much affected by the $H_0$ tension. We investigate what impact this tension brings to cosmological bound on neutrino masses by assuming a model with modified recombination which has been shown to resolve the tension. We argue that constraints on neutrino masses become significantly…
Risaliti, Lusso \& collaborators have constructed a high-redshift Hubble diagram of supernovae (SNe); quasars (QSO) and gamma-ray bursts (GRB) that shows a "$\sim 4 \, σ$ tension with the $Λ$CDM model" based on a log polynomial cosmographic expansion (Risaliti et.al 2018, Lusso et.al 2019). In this work, we demonstrate that the log polynomial expansion generically fails to recover flat $Λ$CDM beyond $z \sim 2$, thus undermining the $\sim 4 \, σ$ tension claim. Moreover, through direct fits of both the flat $Λ$CDM and the log polynomial model to the SNe+QSO+GRB dataset, we confirm that the flat…
One problem of the $Λ$CDM model is the tension between the $S_8$ found in Cosmic Microwave Background (CMB) experiments and the smaller one obtained from large-scale observations in the late Universe. The $σ_8$ quantifies the relatively high level of clustering. Bayesian Analysis of the Redshift Space Distortion (RSD) selected data set yields: $S_8 = 0.700^{+0.038}_{-0.037}$. The fit has $3σ$ tension with the Planck 2018 results. With Gaussian processes method a model-independent reconstructions of the growth history of matter in-homogeneity is studied. The fit yields $S_8 = 0.707^{+0.085}_{-0…
We use supernovae measurements, calibrated by the local determination of the Hubble constant $H_0$ by SH0ES, to interpolate the distance-redshift relation using Gaussian process regression. We then predict, independent of the cosmological model, the distances that are measured with strong lensing time delays. We find excellent agreement between these predictions and the measurements. The agreement holds when we consider only the redshift dependence of the distance-redshift relation, independent of the value of $H_0$. Our results disfavor the possibility that lens mass modeling contributes a 10…
In this talk I will review the current status of the constraints on the neutrino properties from cosmological measurements, with a particular focus on their mass and effective number. I will also discuss the existing tensions within the context of the \lcdm\ model, including the discrepancies on the Hubble parameter and on the matter fluctuations at small scales, and how neutrinos could help to alleviate the aforementioned problems.
Cosmological tensions in the birthplace of the heliocentric model
University of Sheffield（谢菲尔德大学）；National Observatory of Athens（雅典国家天文台）；Johns Hopkins University（约翰斯·霍普金斯大学）；Space Telescope Science Institute（太空望远镜科学研究所）
There has been a significant interest in modifications of the standard $Λ$ Cold Dark Matter ($Λ$CDM) cosmological model prompted by tensions between certain datasets, most notably the Hubble tension. The late-time modifications of the $Λ$CDM model can be parametrized by three time-dependent functions describing the expansion history of the Universe and gravitational effects on light and matter in the Large Scale Structure. We perform the first joint Bayesian reconstruction of these three functions from a combination of recent cosmological observations, utilizing a theory-informed prior built o…
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 $N_{\rm eff}$ and comment on the long standing $H_0$ and $σ_8$ tensions within this cosmological framework with a wealth of cosmological observations. Inter…
Phantom dark energy as a natural selection of evolutionary processes $\hat{\rm a}$ $\textit{la}$ $\textit{genetic algorithm}$ and cosmological tensions
Within the framework of Unimodular Gravity, we consider non-gravitational interactions between dark matter and dark energy. Particularly, we describe such interactions in the dark sector by considering diffusion models that couple the cold dark matter fluid with the dark energy component, where the latter has the form of a variable cosmological "constant". For the first time, we solve the cosmological evolution of these models from the radiation dominated era to the present day. We show how the diffusion processes take place by analyzing the cosmological evolution of the energy density paramet…
The measurements of the Hubble constant reveal a tension between high-redshift (CMB) and low-redshift (distance ladder) constraints. So far neither observational systematics nor new physics has been successfully implemented to explain this tension away. This paper present a new solution to the Hubble constant problem. The solution is based on the Simsilun simulation (relativistic simulation of the large scale structure of the Universe) with the ray-tracing algorithm implemented. The initial conditions for the Simsilun simulation were set up as perturbations around the $Λ$CDM model. However, un…
We present an improved Minimal Variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. We also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant $H_o$; this is important given the tension between …
Based on tensions between the early and late time cosmology, we proposed a double valued cosmological constant which could undergo a phase transition in its history. It is named "double-$Λ$ Cold Dark Matter": $ΛΛ$CDM. An occurred phase transition results in (micro-) structures for the dark sector with a proper (local) interaction. In this paper, inspired by the physics of critical phenomena, we study a simplified model such that the cosmological constant has two values before a transition scale factor, $a_t$, and afterwards it becomes single-valued. We consider both the background and perturba…
The possibility that the $H_0$ tension is a sign of a physics beyond the $Λ$CDM model is one of the most exciting possibilities in modern cosmology. The challenge of solving this problem is complicated by several factors, including the worsening of the tension on $σ_8$ parameter when that on $H_0$ is raised. Furthermore, the perspective from which the problem is viewed should not be underestimated, since the tension on $H_0$ can also be interpreted as a tension on the size of the acoustic horizon, $r_s$, which deserves proper discussion. The common approach in the literature consists in propos…
Cosmological tensions can arise within $Λ$CDM scenario amongst different observational windows, which may indicate new physics beyond the standard paradigm if confirmed by measurements. In this article, we report how to alleviate both the $H_0$ and $σ_8$ tensions simultaneously within torsional gravity from the perspective of effective field theory (EFT). Following these observations, we construct concrete models of Lagrangians of torsional gravity. Specifically, we consider the parametrization $f(T)=-T-2Λ/M_P^2+αT^β$, where two out of the three parameters are independent. This model can effic…
Local measurements of the Hubble parameter obtained from the distance ladder at low redshift are in tension with global values inferred from cosmological standard rulers. A key role in the tension is played by the assumptions on the cosmological history, in particular on the origin of dark energy. Here we consider a scenario where dark energy originates from the amplification of quantum fluctuations of a light field in inflation. We show that spatial correlations inherited from inflationary quantum fluctuations can reduce the Hubble tension down to one standard deviation, thus relieving the pr…
Alternative cosmological models have been under deep scrutiny in recent years, aiming to address the main shortcomings of the $Λ$CDM model. Moreover, as the accuracy of cosmological surveys improved, new tensions have risen between the model-dependent analysis of the Cosmic Microwave Background and lower redshift probes. Within this framework, we review two quantum-inspired non-locally extended theories of gravity, whose main cosmological feature is a geometrically driven accelerated expansion. The models are especially investigated in light of the Hubble and growth tension, and promising feat…
Cosmological tensions in the era of precision cosmology: Insights from Tensions in Cosmology 2025
University of Sheffield（谢菲尔德大学）；University of Malta（马耳他大学）；National Observatory of Athens（雅典国家天文台）；University of Science and Technology of China（中国科学技术大学）；Universidad Católica del Norte（天主教主教大学）
We investigate constraints on some key cosmological parameters by confronting metastable dark energy models with different combinations of the most recent cosmological observations. Along with the standard $Λ$CDM model, two phenomenological metastable dark energy models are considered: (\romannumeral1) DE decays exponentially, (\romannumeral2) DE decays into dark matter. We find that: (1) when considering the most recent supernovae and BAO data, and assuming a fiducial $Λ$CDM model, the inconsistency in the estimated value of the $Ω_{\rm{m,0}}h^2$ parameter obtained by either including or excl…
The Hubble constant ($H_0$) tension is one of the major open problems in modern cosmology. This tension is the discrepancy, ranging from 4 to 6 $σ$, between the $H_0$ value estimated locally with the combination of Supernovae Ia (SNe Ia) + Cepheids and the cosmological $H_0$ obtained through the study of the Cosmic Microwave Background (CMB) radiation. The approaches adopted in Dainotti et al. 2021 (ApJ) and Dainotti et al. 2022 (Galaxies) are introduced. Through a binning division of the Pantheon sample of SNe Ia (Scolnic et al. 2018), the value of $H_0$ has been estimated in each of the reds…
It has been suggested that late-universe dark matter decays can alleviate the tension between measurements of $H_0$ in the local universe and its value inferred from cosmic microwave background fluctuations. It has been suggested that decaying dark matter can potentially account for this discrepancy as it reshuffles the energy density between matter and radiation and as a result allows dark energy to become dominant at earlier times. In this work, we show that the low multipole amplitude of the cosmic microwave background anisotropy power spectrum severely constrains the feasibility of late-ti…
The standard $Λ$CDM model is recently reported to deviate from the high-redshift Hubble diagram of type Ia supernovae (SNe) and quasars (QSOs) at $\sim4σ$ confidence level. In this work, we combine the PAge approximation (a nearly model-independent parameterization) and a high-quality QSO sample to search for the origins of the deviation. By visualizing the $Λ$CDM model and the marginalized $3σ$ constraints of SNe+QSOs into PAge space, we confirm that the SNe+QSOs constraints in both flat and non-flat PAge cases are in remarkable tension with the standard $Λ$CDM cosmology. Next, we investigate…
Yes, for a wide range of cosmological models ($Λ$CDM, non-interacting $w_z$CDM or models with possible interactions between dark energy and dark matter, in either phantom or non-phantom regimes). In the recent past there have been many attempts to solve the tension between direct measurements of $H_0$ and $σ_8 \sqrt{Ω_{0 {\rm m}}}$ from the respective low redshift observables and indirect measurements of these quantities from the cosmic microwave background (CMB). In this work we reconstruct a model independent approach that boils down to different classes of cosmological models under suitable…
