CosmoVerse@Lisbon

In the era of precision cosmology, exploring new and complementary approaches to measure the expansion history of the Universe is crucial to increase the accuracy in the measurements and keep systematic effects under control. A novel approach that provides cosmology-independent constraints on the Hubble parameter is based on the analysis of the differential age evolution of massive and passively evolving galaxies as “cosmic chronometers” (CC).
In this talk, I will present a new measurement of H(z) at z~1.26 obtained from the analysis of a sam- ple of CC extracted from the survey VANDELS. In our work, we explore the feasibility of deriving accurate and robust differential ages from full-spectrum fitting in the range 1 < z < 1.5, derive the physical properties of the population, study in details the associated systematic uncertainties, and propagate those to the total error budget. These data are used both to derive a new measurement of the Hubble constant H0 (assuming a cosmological model) and to derive a cosmology independent estimate of the Hubble parameter at z∼1.26. I will conclude discussing how this measurement can contribute to shed some light on the H0 tension, and the potential of this method.

We present an estimate of the bulk flow in a volume of radii 150 200h−1Mpc using the minimum variance (MV) method with data from the CosmicFlows4 (CF4) catalog. The addition of new data in the CF4 has resulted in an increase in the estimate of the bulk flow in a sphere of radius 150h−1Mpc relative to the CosmicFlows3 (CF3). This bulk flow has less than a 0.03% chance of occurring in the Standard Cosmological Model (ΛCDM) with cosmic microwave background derived parameters. Given that the CF4 is deeper than the CF3, we were able to use the CF4 to accurately estimate the bulk flow on scales of 200h−1Mpc (equivalent to 266 Mpc for Hubble constant Ho = 75 km/s/Mpc) for the first time. This bulk flow is in even greater tension with the Standard Model, having less than 0.003% probability of occurring.

We present independent determinations of cosmological parameters using the distance estimator based on the established correlation between the Balmer line luminosity, L(Hβ), and the velocity dispersion (σ) for HII galaxies (HIIG). We also explore in detail the systematic uncertainties associ- ated with HIIG as a cosmological tracer. These results are based on new VLT-KMOS high spectral resolution observations of 41 high-z (1.3 < z < 2.6) HIIG combined with previously obtained data for 45 high-z and 107 local HIIG

The detection of gravitational Waves (GW) has opened a new window for cosmology. The cur- rent tension between the measurement of the Hubble constant H0 from Cosmic Microwave Back- ground and Supernova analyses makes an independent, standard siren measurement of H0 from gravitational waves particularly interesting. However, up to date the astronomical community has confidently identified only one optical counterpart to a GW event, a neutron star merger, GW170817. In the cases where no counterpart is identified/expected such as Binary Black Hole (BBHs) events, it is possible to use a statistical approach, also known as the “dark siren” method, to produce individually weaker constraints. This method provides a less precise cosmological con- straint on an event-to-event basis, due to the typically large number of galaxies over which one needs to marginalize. Current constraints suggest that from ˜20% to 80% of LIGO/Virgo/KAGRA BBHs are associated with Active Galactic Nuclei (AGN) disks. The claim for a possible association of the BBH merger GW190521 with a flare in the AGN J124942.3+344929, alongside to the several proposed models and mechanisms to make a viable EM counterpart from BBHs in accretion disks suggested this might be a promising endeavor. Therefore, we explore the possibility of Standard Sirens in association with AGN hosts and AGN flares, through an hybrid method between bright and dark sirens. We simulate GW events from future LIGO/Virgo/KAGRA runs and derive the expected constraints in H0, Ωm, and dark energy equation of state parameter w. Depending on the fraction of AGN hosts and BBHs capable of flare we might obtain H0 from from ˜ 10% (pes- simistic) to ˜ 3% (optimistic) level in the next few years. We also show that the method could be applied to all possible AGNs hosts not requiring a flare in the GW localization area to prospect the cosmological constraints.

In recent years, quasars have shown to be standardizable candles, allowing us to extend the Hub- ble Diagram from the Supernovae Ia range (z ˜ 0-1.5) up to very high redshift (z ˜ 6), and therefore explore the expansion history of the Universe at previously uninvestigated epochs. This implemen- tation has shown the presence of a strong tension (>4σ) with a standard flat ΛCDM model, and indications in favor of Interacting Dark Sector alternative models. In this talk, I will first discuss the reliability of quasars as standard candles, focusing on possible sources of biases and systemat- ics and how we can address them to build a valid quasar sample for cosmology. I will then focus on the observed dispersion of the luminosities relation, describing its possible causes and if and how we can lower it to get more precise distance measurements. Finally, I will discuss the high-redshift tension with the standard flat ΛCDM model.

We shall review the landscape of dark energy models, focusing on non-minimal cosmologies which exhibit a coupling among the dark sectors of the theory, that is, an energy flow among dark energy and dark matter. Such a very appealing possibility may alleviate the current mismatch in the observations of the Hubble constant. It could also play a non-negligible role in the recent results of the JWST-telescope

I will review local measurements of the Hubble constant using the distance ladder and data from Gaia EDR3, HST, JWST, Pantheon +, SH0ES and a range of techniques and tools.

The extragalactic distance ladder measures the Hubble constant using type-Ia supernovae whose absolute calibration relies on stellar standard candles, such as classical Cepheids and the TRGB method. Understanding the implications of the Hubble constant tension requires careful consideration of the systematics of stellar standard candles. This presentation reviews recent improvements in the quantification and mitigation of systematics affecting stellar standard candle distances. In turn, I make the case that both TRGB and Cepheids provide consistent H0 values that are in significant tension with Planck.

To understand dark matter and energy, large cosmological surveys are designed to reach a few percent precision. To be fully exploited, this large quantity of data needs to be analyzed in light of cosmological simulations. Preliminary analyses brought out tensions between the standard cosmological model and observations. Reaching a 1% precision, systematics of the same order of magnitude, due to our cosmic environment, our survey specificities and our tool properties, probably rise out. Analyses need to be fueled with a new type of cosmological simulations designed to reproduce our cosmic environment. Such simulations, that I named CLONES (Constrained LOcal & Nesting Environment Simulations), could provide a robust methodological framework to minimize these systematic errors. I will introduce the CLONES giving a few study examples. CLONES are a promising tool to increase our capacity to evade biases in future survey analyses.

I will start my talk with a brief critical review of cosmological proposals put forward as potential so- lutions to the Hubble constant tension. I will argue that the lack of decisive observational evidence supporting any of the current models should motivate our community to reassess the risk-to-gain ratio of this line of research and perhaps restore a balance between the efforts put in testing a wide range of possible testing systematic effects in the measurements of the Hubble constant and ad hoc modifications of the standard cosmological model. In the second part of my talk, I will discuss a new reanalyses of Cepheid and type Ia supernova data used in the local determination of the Hubble constant. I will show the evidence of a discrepancy between the colour correction of supernovae in the calibration sample and the Hubble flow. This discrepancy is currently an intrinsic tension in the local determination of the Hubble constant and a source of unaccounted systematic errors. I will show that applying supernova standardisation which accounts for this anomaly by resolving two different observationally and theoretically motivated supernova popu- lations related to two progenitor channels and dust extinction in their environments, yields the Hubble constant which is consistent with the Planck value. The new standardisation method is based on a novel Bayesian hierarchical model of type Ia supernovae which explains completely the Hubble residuals arising from the standard method of supernova standardisation in terms of extinction and intrinsic properties of supernovae originating from two observationally motivated populations (fast/slow decliners correlated with old/young stellar populations). I will give a brief overview of this model, the current constraints and the perspectives of using it in cosmological analyses of type Ia supernovae.

I will detail leaps of progress in Type Ia Supernova Cosmology (SNIa) that have culminated in the recent Pantheon+ cosmological analysis of 1701 SNIa light curves. While this SN dataset places strong constraints on dark matter, dark energy and solidify Lambda CDM, Pantheon+ is also used in the recent SH0ES constraints of the local value of the Hubble Constant (the current expansion rate of the universe) that are now in 5sigma tension with the inferred value from the cosmic microwave background. I will detail the formulation of the SN dataset, internal consistency checks, and our robust treatment of systematic uncertainties that have built confidence in the cosmological measurements and that also pave the path for future surveys.

Early Dark Energy (EDE), an additional component of dark energy active in the decade of redshift before recombination, has emerged as one of the most effective models at resolving the Hubble tension. By reducing the size of the sound horizon’ that calibrates CMB and BAO observations, it is able to fit a variety of datasets including the variety of high-H0 measurements, and may shed light upon the yet-unknown nature of dark energy, and even inflation. Yet, it is clear that EDE cannot bethe end of the story’ at least in its current form, as it brings up a number of theoretical and observational issues. In this talk, I will review the current status of EDE models, highlighting both the successes and challenges that EDE is facing, and draw implications of what we have learned about EDE towards establishing a new ``concordance cosmology’’.

I give a review of weak gravitational lensing by the large scale structures also known as cosmic shear. I will take you through the steps taken to extract cosmological information from data and discuss the results from the recent weak gravitational lensing surveys. I will then discuss the tension in the structure growth parameter when comparing the weak lensing results with the cosmic microwave background and their implications.

Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories.

In this talk I will discuss about the global agreement between the most recent observations of the Cosmic Microwave Background temperature and polarization anisotropies. I will point out some emergent anomalies that cannot be fully understood within the standard ΛCDM model of cosmology, hinting at significant unaccounted-for systematics in the CMB data or at basic missed ingredients in the theory. Either way, I will show that these anomalies are responsible for a global “CMB tension” between independent experiments that persists also in extended background cos- mologies and analyze the implications for new physics beyond ΛCDM.

"Cosmological models and their corresponding parameters are widely debated because of the current discrepancy
between the results of the Hubble constant, H0, obtained by SNe Ia, and the Planck data from the cosmic microwave
background radiation. Thus, considering high redshift probes like gamma-ray bursts (GRBs) is a necessary step.
However, using GRB correlations between their physical features to infer cosmological parameters is difficult
because GRB luminosities span several orders of magnitude. In our work, we use a three-dimensional relation
between the peak prompt luminosity, the rest-frame time at the end of the X-ray plateau,
and its corresponding luminosity in X-rays: the so-called 3D Dainotti fundamental plane relation.
We correct this relation by considering the selection and evolutionary effects with a reliable statistical method,
obtaining a lower central value for the intrinsic scatter, σint = 0.18 ± 0.07 (47.1 per cent) compared
to previous results, when we adopt a particular set of GRBs with well-defined morphological features,
called the platinum sample. We have used the GRB fundamental plane relation alone with both Gaussian
and uniform priors on cosmological parameters and in combination with SNe Ia and BAO measurements
to infer cosmological parameters like H0, the matter density in the universe (ΩM), and the dark energy
parameter w for a wCDM model. Our results are consistent with the parameters given by the Lambda cold dark
matter model but with the advantage of using cosmological probes detected up to z = 5, much larger than
the one observed for the furthest SNe Ia. We also show how many GRBs we would need to have
if we aim to achieve the precision of SNe Ia as reached by the Pantheon sample
by introducing a new GRB fundamental plane in optical wavelength."

The standard analysis of the Pantheon+ and SH0ES SnIa samples assumes that the SnIa absolute magnitude parameter M can be standardized to a single and isotropic value. If these assumptions are withdrawn and in particular if a transition of M is allowed at some distance scale from M_< at low distances to M_> at high distances then the quality of fit to the Pantheon+ data improves significantly and the two best fit values M_<, M_> are at about 2-3\sigma tension with each other. The origin of this effect is a combination of the uncorrected volumetric redshift bias systematic and a mild transition signal of the intrinsic SnIa luminosity at a distance of about 20Mpc. The implications of this inhomogeneity for the Hubble tension and the best fit values of cosmological parameters will be discussed. The isotropy of the SnIa absolute magnitude parameter and its dependence on distance bins will also be discussed using the hemisphere comparison method.

"In the absence of a fundamental and well defined theory, several parameterizations of cosmological functions have been suggested to get insights of the general DE behaviour and hence to look for possible deviations from the cosmological constant.
Even though these parametric forms usually provide a better fit to the data, they have the limitation of assuming an a priori functional form which may lead to some bias or misleading model-dependent results, regardless of the DE nature. In this talk, to avoid these possible issues, non-parametric and model-independent techniques are presented, i.e. Gaussian process and Artificial Neural Networks. They allow us to extract information directly from the data to detect features within cosmological functions, for instance a decrease in the dark energy density component at early times and a transition to the phantom divide-line in the EoS."

We constrain the viable models of Horndeski gravity after the GWs events by resorting to the Witten positive energy theorem. We find that the free function G3(ϕ,X) in the Lagrangian is con- strained to be a function solely of the scalar field, G3(ϕ). In addition,relations among the free functions are found. Other criteria for stability are also analysed, such as the attractiveness of gravity, and the Dolgov-Kawasacki instability. Some applications for cosmology are discussed.

Using a combination of mathematics and data analysis, I will explain why evolution of the Lambda- CDM cosmological parameters with effective redshift is expected. I will review observations show- ing such trends and explain why they tilt the cosmological tensions debate away from systematics and towards missing physics.

Weak lensing cosmology stands at a crossroads, with cosmological tensions between cosmic shear experiments and those from Planck’s analysis of the CMB hinting at either undiscovered physics or unaccounted-for systematics. In response to this mystery, we present a new weak lensing statis- tic capable of vastly enhancing cosmological inference. The “lensing PDF” - or the distribution of projected structures in various density bins - directly probes non-Gaussianities in large-scale structure, extracting extra cosmological information beyond the reach of two-point statistics con- ventionally employed in this field. Using numerical simulations tailored to match upcoming data from LSST, I demonstrate that lensing PDFs outperform standard lensing probes by >90% in con- straining the matter energy density and amplitude of the matter power spectrum. This approach consequently presents a promising means to shed light on the observed cosmological discordance.

We study the performance of three pairs of tilted ΛCDM cosmological models, two pairs allowing for non-flat spatial hypersurfaces with CMB temperature and polarization power spectrum data (P18) from Planck, P18 lensing (lensing), and non-CMB data (non-CMB). For the six models, we measure cosmological parameters and study whether or not pairs of the data sets are mutually consistent in these models. Half of these models allow the lensing consistency parameter AL to be an additional free parameter, while the other three have AL=1. In the tilted non-flat models with AL=1 we find differences between P18 data and non-CMB data cosmological parameter constraints. While both P18 data and non-CMB data separately favor a closed geometry when P18+non-CMB data are jointly analyzed the evidence in favor of non-flat hypersurfaces subsides. Differences between P18 data and non-CMB data cosmological constraints subside when AL is allowed to vary. From the most restrictive P18+lensing+non-CMB data combination we get almost model- independent constraints and find that the AL>1 option is preferred over the Ωk<0 one, with the AL parameter, for all models, being larger than unity by ∼ 2.5σ. According to the deviance information criterion, in the P18+lensing+non-CMB analysis, the varying AL option is on the verge of being strongly favored over the AL=1 one, which could indicate a problem for the standard tilted flat ΛCDM model

The arrival time of photons in the different lensed images of distant quasars can be measured from long and well-sampled light curves. This has been pioneered by the COSMOGRAIL, H0LiCOW and TDCOSMO programs and will soon been follow-up with Rubin-LSST. Time delays are inversely proportional to H0 and agree with local H0 measurements such as SH0ES. I will present some of the recent results from the TDCOSMO collaboration and show how the field of time delay cosmography can be used in the future to measure H0 and narrow down the error bars.

It is quite possible that the tensions between various observational datasets and theoretical predictions of the Standard Model of Gravity and Cosmology, such as the H0 and S8 tensions, could be a sign that we are approaching New Physics. Among the various possible solutions/alleviations, the ones bases on modifications /extensions of General Relativity may be the most promising.

The cosmic neutrino background, a relic of the early universe, represents a fundamental aspect of cosmic particle physics. This talk provides an overview of the current status and perspectives regarding the cosmic neutrino background, while also exploring the possibility of resolving current tensions.

Monte Carlo (MC) algorithms are commonly employed to explore high-dimensional parameter spaces constrained by data. All the statistical information obtained in the output of these analyses is contained in the Markov chains, which one needs to process and interpret. The marginaliza- tion technique allows us to digest these chains and compute the posterior distributions for the parameter subsets of interest. In particular, it lets us draw confidence regions in two-dimensional planes, and get the constraints for the individual parameters. It is very well known, though, that the marginalized results can suffer from volume effects, which can introduce a non-negligible bias into our conclusions. The impact of these effects are barely studied in the literature. In this talk I first illustrate the problem through a very clear and simple example in two dimensions, and sug- gest the use of the profile distributions (PDs) as a complementary tool to detect marginalization biases directly from the MC chains. I apply this method to four cosmological models: the standard ΛCDM, early dark energy, coupled dark energy and the Brans-Dicke model with a cosmological constant. I discuss the impact of the volume effects on each model and the cosmological tensions, using the full Planck 2018 likelihood, the Pantheon compilation of supernovae of type Ia and data on baryon acoustic oscillations. This test is very efficient and can be easily applied to any MC study. It allows us to estimate the PDs at a derisory computational cost not only for the main cosmological parameters, but also for the nuisance and derived ones, and to assess the need to perform a more in-depth analysis with the exact computation of the PDs. This talk is based on Phys.Rev.D 106 (2022) 6, 063506 [arXiv:2203.16285].

In this talk, inspired by the recent conjecture originated from graduated dark energy (gDE) that the universe has transitioned from anti-de Sitter vacua to de Sitter vacua in the late universe, we will discuss the superior features of the $\Lambda_{\rm s}$CDM model, which extends the standard $\Lambda$CDM model by a cosmological constant ($\Lambda_{\rm s}$) that switches sign at a certain redshift $z_\dagger$, over the standard $\Lambda$CDM model in the light of observational data. We will first discuss that, when the consistency of $\Lambda_{\rm s}$CDM with the CMB data is ensured, $H_0$ and $M_B$ values are inversely correlated with $z_\dagger$ and reach $H_0\approx73.4~{\rm km\, s^{-1}\, Mpc^{-1}}$ and $M_B\approx-19.25\,{\rm mag}$ for $z_\dagger=1.6$, in agreement with the SH0ES measurements, and $H(z)$ exhibits an excellent fit to the Ly-$\alpha$ data. We will then show that the CMB alone is not able to well constrain $z_\dagger$ and thus discriminate between $\Lambda_{\rm s}$CDM and $\Lambda$CDM models, but the CMB+BAO data set favors the sign switch of $\Lambda_{\rm s}$ providing the constraint: $z_\dagger=2.44\pm0.29$. The further observational analysis using more data sets reveals that $\Lambda_{\rm s}$CDM is significantly favored over $\Lambda$CDM, and it resolves various tensions that prevail within $\Lambda$CDM; for instance, the CMB+Pan data set with $M_B$ prior gives $z_\dagger=1.784^{+0.14}_{-0.18}$ along with $H_0\approx72.38^{+0.98}_{-1.10}~{\rm km\, s^{-1}\, Mpc^{-1}}$, $S_8=0.785\pm0.012$, and $M_B=-19.290^{+0.026}_{-0.029}$, all of which are consistent with their local measurements, and moreover that the physical baryon density value, $\omega_b$, better agrees with the BBN constraints on it and $H(z)$ exhibits excellent fit to the Ly-$\alpha$ data. While using the CMB+Pan+Ly-$\alpha$ data set provides us with the similar constrains, inclusion of the low-redshift BAO data, i.e., using CMB+Pan+BAO data set, leads to some compromise in these improvements. We will close the talk with a discussion on some other observational aspects and theoretical implications of the $\Lambda_{\rm s}$CDM model. This talk is based on the works Graduated dark energy: Observational hints of a spontaneous sign switch in the cosmological constant" [Akarsu, Barrow, Escamilla, and Vazquez, PRD 101 (2020) 063528],Relaxing cosmological tensions with a sign switching cosmological constant" [Akarsu, Kumar, Ozulker, and Vazquez, PRD 104 (2021) 123512], and ``Relaxing cosmological tensions with a sign switching cosmological constant: Improved results with Planck, BAO and Pantheon data" [Akarsu, Kumar, Ozulker, Vazquez, and Yadav, arXiv:2211.05742] and several ongoing works by an extended group of leading researchers in the field of cosmology.

Reconciling the standard model’s theoretical predictions with precision measurements from mul- tiple probes stands as one of the most pressing challenges of modern cosmology. During the last decade, increasing evidence for persistent discrepancies in the value of cosmological param- eters when inferred from model-dependent and -independent probes opened the door for a new paradigm. In this talk, I will address whether (part of) the cosmological tensions can be attributed to missing physics in the standard model. In particular I will focus on tests of different models with interactions between dark energy and dark matter.

We investigate the dark energy in the Weyl geometric gravity, which is based on the introduction of a Weyl connection to describe the gravitational properties of the space-time. We consider the case in which the Lagrangian is given by the sum of the square of the Weyl scalar, of the strength of the field associated to the Weyl vector, and a conformally invariant geometry-matter coupling term, constructed from the matter Lagrangian and the Weyl scalar. The action is linearized in the Ricci scalar by introducing an auxiliary scalar field. After substituting the Weyl scalar in terms of its Riemannian counterpart, the quadratic Wedyl action is defined in Riemann geometry, and involves a nonminimal coupling between geometry and matter. The field equations are obtained by varying the action with respect to the metric, the scalar field, and the Weyl vector. The cosmological implications of the Weyl geometric gravity field equations are investigated for different forms of the Weyl vector-matter Lagrangian coupling functions. From the generalized Friedmann equations of the model, obtained by assuming that the background Riemannian metric is of the Friedmann- Lemaitre-Robertson-Walker type, an effective geometric dark energy component can be generated, with the effective, geometric type pressure. A comparison with the standard ΛCDM model is also performed, and we find that the Weyl geometric gravity type cosmological models can give an acceptable description of the cosmological observations.

The effect of gravitational lensing of the cosmic microwave background (CMB) provides a unique opportunity to obtain a picture of the gravitational potential of the large-scale structure of the Universe at very high redshifts. Tomographic cross-correlation of the gravitational potential with other tracers of the large-scale structure at known redshifts allows tracing the evolution of the structure and testing cosmological models. However, the analysis of upcoming data will require a very good understanding of any systematic errors that may bias cross-correlation measurements. In this talk we will present studies of systematic errors arising from cross-talk between redshift bins of galaxies with photometric redshift uncertainties. We show their impact on the cross-correlation measurement and cosmological parameter estimates for future data sets. We also present an efficient method for removing the errors.

It has been theorized that Dynamical Dark Energy (DDE) could be a possible solution to the Hubble tension. To avoid the degeneracy between the Hubble parameter H0 and the sound horizon scale rd, we use their multiplication as one parameter c/(H0rd). To the BAO points we add the SNIa Pantehon dataset and GRB dataset and the points from the CMB priors. We use different DE parametrizations to constrain the cosmological parameters and we compare the results based on statistical measures. We compare the results with the ones obtained by marginalizing over the H0⋅rd by redefining the likelihood in a BAO and SNIa datasets.

"In this talk, we overview dark energy models with negative energy density values in the past can alleviate the H0 tension. We investigate whether two minimal extensions of the ΛCDM model, to- gether or separately, can successfully realize such a scenario: (i) the spatial curvature, which, in the case of spatially closed universe, mimics a negative density source and (ii) graduated and simple- graduated dark energy, which promote the null inertial mass density of the usual vacuum energy to an arbitrary function/constant–if negative, the corresponding energy density decreases with redshift similar to the phantom models, but unlike them crosses below zero at a certain redshift. We find that, a spatially closed universe along with a simple-gDE of positive inertial mass density, which work in contrast to each other, results in minor improvement to the H0 tension. The joint dataset, BAO+SN+H+PLK presents no evidence for a deviation from spatial flatness but almost the same evidence for a cosmological constant and the simple-gDE with an inertial mass density of order O(10ˆ{-12}) eVˆ4. We will talk about further inertial mass density parameterizations such as linear/oscillatory generalizations in scale factor as well as redshift of the vacuum energy. We then will close the talk with the possibility of obtaining effective sources such varying inertial mass densities from modified theories/extensions of gravity as like the constant inertial mass density (Simple gDE ) arises from barotropic perfect fluid via the energy-momentum squared gravity of the logarithmic form.
This talk is based on the works:
[1] Simple-graduated dark energy and spatial curvature, G. Acquaviva, Ö. Akarsu, N. Katirci, J. A. Vazquez, Phys. Rev.D 104 (2021) 2, 023505, 2104.02623 [astro-ph.CO]. [2] Screening Λ in a new modified gravity model, Ö. Akarsu, J. D. Barrow, C.V.R. Board, N.M. Uzun, J. A. Vazquez, Eur.Phys.
J.C 79 (2019) 10, 846, 1903.11519 [gr-qc]. [3]Graduated dark energy: Observational hints of a spontaneous sign switch in the cosmological constant, Ö. Akarsu, J. D. Barrow, L.A. Escamilla, J.
A. Vazquez, Phys.Rev.D 101 (2020) 6, 063528 1912.08751 [astro-ph.CO]. [4] Dynamical analysis of logarithmic energy-momentum squared gravity, G. Acquaviva, N. Katirci, 2203.01234 [gr-qc]."

We propose a cosmological model that predicts the variation of the fine structure constant α with redshift, where the electromagnetic sector couples to the kinetics of a canonical scalar field ϕ. This is a generalization of the usual linear dependence of the interaction term on ϕ. This theory can be seen as a disformal coupling with radiation, where the conformal factor depends on the kinetic term of the scalar source. We have studied the phenomenology of the model by particularizing the scalar field as the quintessence component driving the current acceleration. We found the remarkable feature that the evolution of α follows the Hubble flow, slowing down at late times during dark energy dominance. We have constrained the free parameters with measurements of BBN, Planck, quasar absorption spectra, atomic clocks, and tests of the weak equivalence principle. The variation of the recombination redshift leads to a geometric degeneracy between $\alpha$ and $H_0$, which can tackle the Hubble tension.

"When N-body simulations deal with dark energy, they consider its effect only at the background level, modifying the Hubble expansion. A notable exception is the K-evolution code which simulates k-essence models with a low sound-speed using the effective field theory approach at the non-linear level. It has been demonstrated that this leads to divergences. Hence, a few authors recently proposed to investigate this issue by developing a code which can simulate a dark energy fluid in a way analogous to what normally done with dark matter and baryons modifying the Euler equation taking into account pressure contributions.
In this talk I will explore the effects of this additional term in the formalism of the spherical collapse model and show how the evolution of perturbations compare to the standard equations and how the halo mass function is modified. A modification in the evolution of perturbations, also taking into account dark energy perturbations, will lead to a different normalization of the matter power spectrum, sigma8. This quantity can be further constrained with observed measurements of the halo mass function and indicate whether the sigma8 tension is alleviated or enhanced."

Galaxy clustering is one of the pillars of current cosmological parameter constraints, in particular for understanding the properties of the late universe and how they relate to those predicted from early universe measurements, in combination with cosmic shear observations. In photometric surveys, spurious correlations may be introduced by the spatial distribution of observational con- ditions and astrophysical properties over the sky. We make a short overview of how this problem is tackled in the Dark Energy Survey, as well as in other projects of its kind.