How many h are there? And what do they mean?

• Licia Verde (Instituto de Ciencias del Cosmos (ICC))

The current expansion rate of the Universe is captured by the so-called Hubble constant, or its dimensionless equivalent, "little h", which is a key parameter in the, extremely successful, standard model of cosmology. The Hubble constant  relates measurements of the expansion history of the Universe to its components, and “little h” appears in all astrophysical quantities which measurement or calibration somewhat depend on the background cosmology. The ‘Hubble tension’ has motivated the exploration of extensions to the standard cosmological model in which higher values of H0 can be obtained from CMB measurements and galaxy surveys. The Hubble trouble, however, goes beyond H0.  Modifications invoked to address the Hubble tension affect other quantities too, such as cosmic times, age of the Universe and the matter density. Any  Hubble trouble has implications well beyond  H0 itself. I will recap some recent results and  try to look at the tension in both a model-dependent and model independent way.

Constraints on Cosmological Expansion With Type Ia Supernovae

• Daniel Scolnic (Duke University)

I will discuss recent results from the Pantheon+ team on constraining multiple cosmological parameters with Type Ia supernovae. The Pantheon+ and SH0ES teams released likely their final major update to the measurement of the Hubble constant, which parameterizes the current expansion rate of the universe. The result is in 5sigma tension with constraints from the Cosmic Microwave Background. I will overview the new measurements on the local side, and discuss the extensive work on systematic covariances between these measurements. I will go over various past challenges to the local-side measurement and detail how our new analyses have addressed them. I will then discuss next steps and challenges, and particularly what we will learn from upcoming analyses like DES, and future ones like LSST and Roman.

Toward Cosmological Concordance with New Physics in the Dark Sector

• Colin Hill (Columbia University)

I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets, motivated by discrepancies between some measurements of the cosmic expansion rate (H_0) and the matter clustering amplitude (S_8). Particular attention will be paid to models invoking new physics in the high-redshift universe, including quasi-accelerating early dark energy models (and extensions thereof) and generalized decaying particle scenarios. In particular, I will discuss constraints on these models derived using the latest CMB measurements from the Atacama Cosmology Telescope (ACT) and from the Planck satellite, amongst other data sets. I will conclude with a look ahead to forthcoming CMB data from ACT, which will provide a powerful test of these scenarios in the low-noise, high-resolution regime.

Addressing cosmological tensions with new emerging probes: a perspective from cosmic chronometers

• Michele Moresco (University of Bologna)

In the era of precision cosmology, exploring new and complementary approaches to measure how the Universe (and the structures therein) have evolved is of fundamental importance, to increase the accuracy in the measurements and keep under control systematic effects. In this talk, I will present a novel approach to obtain constraints on the expansion rate of the Universe based on the differential age evolution of "cosmic chronometers". The strength of this method is that it allows a direct measurement of the Hubble parameter H(z) without relying on any cosmological assumptions, providing an ideal framework to test cosmological models.

Measuring H0 with strongly lensed quasars

• Leon Koopmans (Kapteyn Astronomical Institute)

Time-delay cosmography with lensed quasars is the only single-step method to measure H0. It has its own advantages and drawbacks that I will review, before presenting the different avenues adopted by the TDCOSMO collaboration to improve results. Part of this effort resides in time delay measurements obtained at high temporal cadence for 50 lensed quasars, illustrating the need for medium-size telescope(s) to complement LSST.

Inhomogeneous Hubble diagram from vector K-mouflage

• Philippe Brax (CEA Saclay)

I will present the Hubble diagram for a Universe where dark matter is universally charged under a dark non-linear electromagnetic force which features a screening mechanism of the K-mouflage type for repulsive forces. I will explicitly show that the cosmological evolution generates an inhomogeneous Hubble diagram that corresponds to a curvature dominated expansion at short distances and converges to the cosmological one of ΛCDM. We discuss the potential impact of this inhomogeneous profile on the Hubble tension.

A uniform Zwicky Transient Facility-tip of the red giant branch distance ladder Implications for the Hubble constant

• Suhail Dhawan (University of Cambridge)

The Hubble tension is arguably the largest open question in modern cosmology. It could be a sign of new cosmological physics or unknown sources of systematics. To definitively answer this question, we need percent level measurements of the local distance scale. In this talk, I will present our recent work on calibrating the absolute luminosity of Type Ia supernovae from the wide-field Zwicky Transient Facility. This distance ladder is uniform in that both the calibrator and Hubble flow SNe Ia are observed with a single, untargeted survey, which sidesteps the two largest systematics in the local distance ladder, i.e. photometric cross-calibration and selection biases depending on host environment. Finally, I'll preview the upcoming work on building this distance ladder in the JWST era.

Cosmological tension analyses in extended theories of gravity: artificial neutral path

• Celia Escamilla-Rivera (Nuclear Institute of Science (Instituto de Ciencias Nucleares). Universidad Autonoma de Mexico. ICN-UNAM)

The current cosmological probes have provided an extraordinary confirmation of the standard LCDM cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this talk I will list a few interesting new cosmological models in the direction of extended theories of gravity that could solve this tension and discuss how the new computational techniques will be crucial in this role.

Large-Scale Anomalies in the Cosmic Microwave Background Current Status, Future Prospects, and Possible Explanations

• Yashar Akrami (IFT Madrid & CWRU, USA)

Even though the current observational data show an extremely high level of agreement with predictions of the standard model of cosmology, LambdaCDM, the cosmic microwave background (CMB) temperature fluctuations measured by the WMAP and Planck satellites have shown a number of persistent anomalous features on large-angular scales that are unexpected or extremely unlikely in LambdaCDM cosmology. These anomalies, which are properties of the observed sky and not instrumental artefacts, are all related to violation of statistical isotropy, and even though they could, individually taken, be statistical flukes, they may also be hints of new physics beyond the standard cosmological model. In this talk, after providing a critical review of the CMB large-angular-scale anomalies, their history and their current status, I will discuss some of the existing explanations for the features, ranging from the fluke hypothesis and astrophysical foregrounds within LambdaCDM to different physical models beyond the standard picture, in particular the possibility that the Universe has a non-trivial topology, and will review phenomenological expectations for each explanation. I will argue that, in addition to the new perspectives on existing data that the powerful and continuously advancing computational and statistical techniques may provide, it is also essential to investigate the anomalies further with upcoming and future high-precision cosmological data, including observations of the CMB polarisation and the cosmic large-scale structure. This is because any observations of similar or related anomalies in any data sets other than the CMB temperature sky will ameliorate concerns about look-elsewhere penalties for the a posteriori statistical characterization of the CMB temperature anomalies while dramatically increasing the statistical significance of the features to a level which will inevitably force us to revise or rethink the standard model of cosmology. Finally, I will discuss potential connections between the CMB anomalies and the recently reported tensions in the measured values of the cosmological parameters of the LambdaCDM model and argue that a combination of these tensions and anomalies may provide a smoking gun for the existence of new physics beyond the standard model of cosmology.

"Hubble tension: Understanding the theoretical uncertainties of TRGB calibrations theoretical uncertainties of TRGB > calibrations"

• Ippocratis Saltas (CEICO, Institute of Physics of the Czech Academy of Sciences, Czechia)

Inferring cosmological parameters from Baryon Acoustic Oscillations datasets

• Denitsa Staicova (Institute for Nuclear Research and Nuclear Energy, BAS)

Baryon acoustic oscillations (BAO) involve measuring the spatial distribution of galaxies to determine the growth rate of cosmic structures. In this talk we discuss the use of different BAO dataset to infer the parameters of different cosmological models. Explicitly, we use BAO + Chronometers data, the Pantheon type Ia supernova, and the Hubble diagram of gamma-ray bursts and quasars to put a limit on the Hubble constant in LCDM, OkCDM and wCDM . Then we marginalize over H0rd to infer the parameters of a set of dark energy models.

Towards solutions to the Hubble problem beyond Einstein's Gravity

• Miguel Zumalacárregui (Max Planck Institute for Gravitational Physics - Albert Einstein Institut)

Discrepant measurements of the Hubble parameter may signal physics beyond the standard cosmological model. I will present different mechanisms to solve the Hubble problem in viable theories beyond General Relativity, testing them against cosmological data and discussing their implications for precision tests of gravity. Among them, a simple model relying on an enhanced strength of gravity at early times reduces the Planck+BAO tension with SH0ES from 4.4 sigma of LCDM to 2.6 sigma (2020 data). While further model building is required to fully resolve the H0 problem, these examples show the wealth of possibilities to solve cosmological tensions beyond Einstein's General Relativity.

Next generation cosmological analysis with nested sampling

• Will Handley

A 1% calibration of the Galactic Cepheid Luminosity scale based on cluster Cepheids strengthens the Hubble tension

• Richard Anderson

I present our recent 1% calibration of the Galactic Leavitt Law (period-luminosity calibration) based on Gaia astrometry of Cepheid-hosting open star clusters as well as individual Cepheids (Cruz Reyes, Anderson et al. in prep.). We identified host clusters in the vicinity of Cepheids using our own clustering method to identify clusters whose average parallax can be safely used in lieu of Cepheid parallaxes for Leavitt law calibration. This method provides average cluster parallaxes with typical uncertainties of ~ 6 micro arcsec for clusters, including angular covariance terms and improving by a factor of ~2.8 on the typical uncertainty of Cepheid parallaxes used for Leavitt law calibration. Using the LMC for comparison, we show that cluster parallaxes are accurately corrected for known Gaia parallax systematics by applying the Lindegren et al. (2021) based on quasars. Hence, additional (beyond Lindegren et al.’s) corrections for parallax offsets that are required for individual Cepheids are not required for average cluster parallaxes. This allows us to calibrate the Milky Way Leavitt law to unprecedented accuracy in a variety of photometric bands and reddening-free Wesenheit magnitudes while simultaneously solving for the residual individual Cepheid parallax offset. Using two photometrically independent sets of Wesenheit magnitudes, we measure the most precise value for the Cepheid parallax offset to date with a significance of 6 sigma. At the same time, we determine the absolute magnitude of Solar metallicity Cepheids of 10 day period to an accuracy as good as 1%, exclusively relying on data of Milky Way Cepheids without a need for data from other galaxies or the distance ladder. Importantly for the Hubble tension, we find a Cepheid luminosity scale in 0.9 sigma agreement with the same number determined by the SH0ES team (Riess et al. 2022) based on an extragalactic distance ladder fit as used to determine the Hubble constant. Our methodology is maximally different from the SH0ES distance ladder, yet obtains results consistent to within 1 sigma and at an accuracy of 1%. This lends strong support to the veracity of the Hubble tension and shows that Gaia astrometry can deliver on its potential to calibrate the Cepheid luminosity scale to better than 1% in future data releases.

Cosmological Constraints using Alternative Hubble Expansion Tracers

• Manolis Plionis (NOA)

A possible non-linear solution to the S8 tension

• George Efstathiou

I will review the evidence for a low value of S8 from cosmic shear. I will then argue that the discrepancy with the Planck value of S8 may be a caused by uncertainties in the theoretical predictions for cosmic shear arising from the  modelling of the mass fluctuations on small scales. In other words, the S8 discrepancy may reflect a tension between small and large scales rather than a tension between physics at early and late times.

The Dark Energy Survey and the S8 tension

• Alexandra Amon (Stanford U)

"I will present the cosmological weak lensing results from the Dark Energy Survey (DES) using its first three years of data taken using the Dark Energy Camera on the 4m Blanco telescope. This analysis spans the full DES footprint, roughly 1/8th of the night sky, with the final galaxy catalogue containing more than 100 million galaxies in riz photometric bands, constituting the most powerful weak lensing dataset to date. The comparison of DES cosmological constraints on dark matter and dark energy from WL and LSS in the low-redshift Universe to CMB constraints provides an unprecedented test of the standard cosmological model, across high and low redshift. I will mention the main challenges that our analysis is susceptible to, and the summarise the approach our team took to account for these and deliver robust cosmological constraints. I’ll contextualise these with other low S8 results in the field. Finally, I’ll present a plausible solution to the S8 tension. "

Modified gravity with 2 d.o.f. as a tool to address tensions in cosmology

• Shinji Mukohyama (Yukawa Institute for Theoretical Physics, Kyoto University)

How to address tensions in cosmology by modified gravity with 2 d.o.f.

• Antonio De Felice

Current and Future Constraints on H0 from Infrared SBF

• John Blakeslee

We recently published a new measurement of the Hubble constant H0 determined from distances to over 60 early-type galaxies out to 100 Mpc measured by the Surface Brightness Fluctuations (SBF) method using data from the WFC3 Infrared Channel on the Hubble Space Telescope (HST). More than a third of these galaxies have hosted well-measured Type Ia supernovae, and we use these to do detailed comparisons of SBF and SNIa distances. If we recalibrate SNIa using SBF, we find a steeper dependence of supernova peak luminosity on decline rate in early-type galaxies, but the resulting value of H0 is indistinguishable from the values given independently by SNIa and SBF when each are calibrated from Cepheids. We discuss these recent SBF results from HST/WFC3 as well as the excellent prospects for a fully independent TRGB-calibrated SBF precision measurement of H0 using JWST.

Tensions with  cosmological singularities: Should we try to avoid their appearance?

• Alexander Kamenshchik (Bologna University)

The appearance of an initial (and sometimes also a final) cosmological singularity in practically all realistic models of the evolution of the universe is distinguishing feature of the modern cosmology. Tensions concerning  this question are always present.There are attempts to construct cosmological models where the geometry is always regular. However, some approaches based on the description of the possible passage through the singularities were also developed recently. We have tried to elaborate a general formalism, telling when it is possible and when the singularity present unsurmountable obstacle.

A robust explanation of CMB anomalies with a new formulation of inflationary quantum fluctuations

• Sravan K. Kumar (Universidade da Beira Interior)

In this talk, we introduce CMB anomalies, especially the hemispherical asymmetry that has been consistently observed by WMAP and Planck data. These anomalies have been extensively discussed in the last decade as a signature of new physics and several scalar field models of inflation have been proposed in this regard. We will present a new understanding of inflationary quantum fluctuations which is model-independent and can robustly explain the hemispherical asymmetry anomaly of the CMB. Based on our approach to the new construction of quantum theory on curved space-time, we also present new predictions with exact numerical values for the CMB temperature fluctuations at low multipoles. We further comment on how one can determine observationally the quantum nature of inflationary fluctuations and how our study will impact the problem of time in quantum cosmology.

Electromagnetic Accelerating Universe

• Paul Frampton

Assuming that the entropy of the contents of the universe saturates the holographic bound, we extend the PBH idea for dark matter within galaxies and clusters of galaxies by populating the universe with extremely masAssuming that the entropy of the contents of the universe saturates the holographic bound, we extend the PBH idea for dark matter within galaxies and clusters of galaxies by populating the universe with extremely massive PBHs having masses extending up to values close to the mass of the universe. The Great Attractor is one possible example of such additional dark matter.sive PBHs having masses extending up to values close to the mass of the universe. The Great Attractor is one possible example of such additional dark matter.

Barrow holographic dark energy and a possible reduction of the Hubble tension

• Mariusz Dabrowski (National Center for Nuclear Research)

I will make some short reminiscent about the geometrical idea of Barrow entropy for black holes and its cosmological horizon applications in the context of dark energy. I will relate it to some other nonextensive entropies such as Renyi and Tsallis – the former being formally related to that of Barrow. Finally, I will show that, amazingly, Barrow holographic dark energy gives a strong Bayesian evidence against ΛCDM and can also weaken the Hubble tension.

A reanalysis of the SH0ES data for H_0: Effects of new degrees of freedom on the Hubble tension

• Leandros Perivolaropoulos (University of Ioannina)

A reanalysis of the SH0ES data for H_0: Effects of new degrees of freedom on the Hubble tension

Increasing Accuracy in the Measurement of H0

• Wendy Freedman (University of Chicago)

The Tip of the Red Giant Branch (TRGB) marks the luminosity at which the core helium flash in low-mass stars occurs, and provides a high-precision and accuracy standard candle. As such, the TRGB offers a critical, independent route to the measurement of Ho. Applied in the halo of galaxies, the TRGB method has a number of advantages: there is negligible extinction by dust, and it has little sensitivity to metallicity and to crowding/blending effects. A Chicago Carnegie Hubble Program (CCHP) calibration of SNe Ho based on HST TRGB measurements yields a value of Ho = 69.8 with an accuracy of 2.5%. A new and upcoming program with the James Webb Space Telescope will measure distances to the same galaxies using the TRGB, Cepheids and carbon stars, and provide robust constraints on current systematics in the measurement of Ho.

The Etherington-Hubble relation

• Fabrizio Renzi (Lorentz Institute for Theoretical Physics, Leiden University)

Hubble tension and quantum gravity effects

• Antonino Marcianò (INFN Frascati LNF)

Following a new pathway to the definition of the Stochastic Quantization, which hinges on the functional similarities between the Ricci-Flow equation and the Stochastic Quantization Langevin equations, while making use of the Arnowitt-Deser-Misner variables and their conjugated Hamiltonian momenta, we have pushed forward a novel approach to investigate, in a geometrical way, the renormalization group equation for gravity theories. The newly derived equations of the Ricci-Flow are understood in terms of the breaking of the diffeomorphism invariance of the classical theory and encode, as the equation associated to the shift vector, the Navier-Stokes equation with a stochastic source, while the fluctuations of the metric tensor components around the equilibrium configurations follow the Kardar-Parisi-Zhang equation, with intermittent statistics of the probabilistic distribution. Within this framework, we show that the cosmological constant appears as a macroscopic effect of the quantum fluctuation of the metric tensor. Finally, inspecting the cosmological Ricci-Flow of the Friedman-Lemaitre-Robertson-Walker metrics, we develop a phenomenological analysis in order to understand if this paradigm can provide a solution to the Hubble tension.

Dynamical Vacuum Energy and Cosmological Tensions

• Emil Mottola (Univ. of New Mexico)

Gravity and general relativity are considered as an Effective Field Theory (EFT) at low energies and macroscopic distance scales. The conformal anomaly of light or massless quantum fields has significant effects on macroscopic scales, which allows the effective value of the vacuum energy to change in space and time. The EFT of vacuum energy thereby replaces the fixed constant Lambda of the classical theory with a dynamical condensate whose natural ground state value in empty flat space is Lambda_eff = 0 identically, without any fine tuning. The implications for spatially inhomogeneous cosmology and resolution of cosmic tensions of LambdaCDM will be discussed.

Resolving tensions in cosmology via the modified measures approach to control vacuum energies

• Eduardo Guendelman (Ben Gurion University)

Introducing modified measures re defines the scalar field potentials while providing spontaneous breaking of scale invariance. In this way one can obtain potentials with two flat regions , one suitable for inflation and the other suitable for the late universe. With two scalar fields the scalar potential can have three flat regions after spontaneous symmetry breaking, one for inflation and the other two for the late universe, showing the possibility of early dark energy, which has been invoked for the resolution of the H0 tension.  Other phenomena present in the modified measures theory, like dark energy from fermions the avoidance of the 5th force problem and the justification in terms of modified measure theory of the the phenomenological model of Afshordi et. al. for the resolution the H0 tension will be discussed.

Comprehensive Measurements of the Local Value of H0 with 1 km/s/Mpc Uncertainty from the SH0ES Team

• Adam Riess (Johns Hopkins U)

Avoiding tensions with a functioning cosmological model

• Pavel Kroupa (Charles University/Bonn University)

The standard model of cosmology relies on the existence of dark matter particles which drive structure and galaxy formation. A rigorous prediction of this model is that each present-day galaxy must be embedded in a massive and extended halo of dark matter particles. The existence of such halos of dark matter can be tested for by applying Chandrasekhar dynamical friction. I will present the results that have been achieved on this with the conclusion that the galaxy--galaxy motion data do not support the existence of these halos. The implication of this tension is that gravitation becomes non-Newtonian on scales beyond the Solar System, in turn implying the need to develop a new cosmological model. Such models, based on Milgromian gravitation, now exist and these automatically solve the Hubble Tension. They also account for the observed very massive galaxy clusters such as El Gordo at a redshift of 0.87 and the closer Bullet cluster, and allow for significant matter density contrasts on spatial scales larger than a few hundred Mpc.

The Cepheid Distance Scale and its Metallicity Dependence

• Louise Breuval (Johns Hopkins University)

Cepheid variables are the best calibrated primary standard candles they are used to standardize the brightness of Type Ia supernovae (SNIa) in nearby galaxies and therefore are central in the determination of the local value of the Hubble constant (H0). The empirical measurement of the Hubble constant obtained by the SH0ES team from the Cepheid-SNIa method is now in 5-sigma tension with the Planck prediction based on the lambda-CDM model. While both estimates have reached a great precision, the source of the Hubble tension remains unknown and suggests evidence of new physics beyond the standard model. In this talk I will describe recent progress on the Cepheid distance scale involving Gaia parallaxes and HST photometry and I will identify the remaining issues and systematics associated with the calibration of their period-luminosity relation. In particular, differences in Cepheid metallicities between the Milky Way, Magellanic Clouds and nearby galaxies hosting SNIa must be corrected in order to provide a consistent distance calibration. Finally I will discuss how future missions and promising techniques are expected to improve again the precision of the empirical H0 value.

A geometric measurement of H0 by the Megamaser Cosmology Project

• Dominic Pesce (Center for Astrophysics | Harvard & Smithsonian)

Water megamasers residing in the accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGN) provide unique tools for bypassing the distance ladder and making one-step, geometric distance measurements to their host galaxies. Â The Megamaser Cosmology Project (MCP) is an international, multi-facility campaign to find, monitor, and map such AGN accretion disk megamaser systems, with the goal of constraining the Hubble constant to a precision of several percent. To date, the MCP has surveyed over 4000 active galactic nuclei for signs of 22 GHz water maser emission, resulting in the discovery of nearly a hundred new megamaser systems (constituting approximately half of all known such systems). 20 of these new systems have been mapped with the VLBA, providing "gold standard" black hole mass measurements, and 10 of them have been extensively observed with both multi-year spectral monitoring and deep VLBI mapping observations for the purposes of making distance measurements. The MCP measurements currently constrain the Hubble constant to 73.9 +/- 3.0 km/s/Mpc independent of distance ladders, the cosmic microwave background, and gravitational lenses, corroborating prior indications that the local Hubble constant exceeds the early-Universe prediction.

Generalizing the Friedmann Model in Light of Cosmological Tensions

• Timothy Clifton (Queen Mary, U. of London)

The recent tensions between cosmological data sets are difficult to accommodate within the standard Friedmann cosmological models. In this talk I will discuss how we might consider more general cosmologies, which could provide more flexibility. I will introduce the mathematical formalisms required to understand Friedmann within this generalized context, and the challenges and difficulties that remain in applying these ideas to the real Universe.

On the Hubble constant tension and its evolution.

• Maria Dainotti (NAOJ)

The Hubble constant (H0) tension between Type Ia Supernovae (SNe Ia) and Planck measurements ranges from 4 to 6 σ. To investigate this tension, we estimate H0 in the ΛCDM and w0waCDM models by dividing the Pantheon sample, a collection of 1048 SNe Ia, into 3, 4, 20, and 40 bins. For the first two divisions, a presence of SNe Ia in the hundreds for each bin is required to effectively account for systematic effects while the last two are required to test for results independence on the bin divisions. A preliminary consistency check is performed, considering the compatibility of contours for 3 and 4 bins with the ones of the total Pantheon sample through a 2-D analysis where the nuisance parameters are H0 and Ω0m. For each bin, a 1-D Monte Carlo Markov-Chain analysis for H0 with the D'Agostini method is performed in order to extract the value of H0, considering a fiducial absolute magnitude of SNe Ia M ~ -19.25. We will show the MCMC application through the Cobaya package for Python. We fit the extracted H0 values with a function describing the redshift evolution g(z)=H'0/(1+z)α, where α is the evolutionary parameter and H'0=H0 at z=0. We find that H0 evolves with redshift, showing a slowly decreasing trend, with α coefficients in the order of 10-2, consistent with zero only from 1.2 to 2.0 σ. A subsequent correction for luminosity distance has been applied and it carries differences of ~2% at z=11.09 (the redshift of the farthest galaxy so far discovered) with the standard ΛCDM luminosity distance. We measure locally a variation of H0(z=1)-H0(z=0)=0.4 km s-1 Mpc-1 in 3 and 4 bins. Interestingly, in the extrapolation of H0 to z=1100, the redshift of the last scattering surface, we obtain values of H0 compatible in 1 σ with Planck measurements independently of cosmological models. Thus, we have reduced the H0 tension from 54% to 72% for the ΛCDM and w0waCDM models, respectively. If the decreasing trend of H0 is real, it could be due to astrophysical selection effects, such as the stretch evolution, or to modified gravity, such as the f(R) theories.

The H0 tension and the physics of the neutrino sector

• Antonio J. Cuesta (University of Cordoba)

Neutrinos are a mysterious sector of the Standard Model with some unanswered fundamental questions. In the first part of our talk we will review the minimal framework with three neutrinos, and what cosmology can tell us about their masses and mixings. However, there also exist non-minimal frameworks which generically assume that the scale of new physics appears is just above 10 TeV (LHC). In this case we typically end up with new light particles, which are promising candidates to explain neutrino anomalies and cosmological tensions. In the second part of the talk we will present one of these scenarios, with a particle, the Majoron, associated to the spontaneous breaking of the lepton number, that significantly changes the thermal history of the Universe in a consistent way with current cosmological data.

Cosmological Tensions: revisiting spatial curvature.

• Alan Coley (Dalhousie Univ.)

Testing the foundations of the concordance model

• Roy Maartens (University of Western Cape)

Tensions in the concordance model are a further motivation to devise and implement tests of a key  foundation of the model - the Cosmological Principle. I will survey current and future tests of the CP.

The multipole structure of the local expansion rate

• Christian Marinoni (Aix-Marseille University)

The failure to converge on a consensus value of the Hubble's constant triggered investigations into the reliability of geometric descriptions of the local spacetime that deviate from the standard cosmological metric. The question that arises is whether metrics with lower symmetries, while still simple, provide a reliable description of the data in the local patch of the universe where global uniformity is violated.

Model-agnostic interpretation of 10 billion years of cosmic evolution traced by BOSS and eBOSS data

• Héctor Gil-Marín

In this talk I present the lastest re-analysis of BOSS and eBOSS spectroscopic survey data and its implication in the current LCDM paradigm. In the first part of the talk I review how the large scale structure of the universe measures cosmological parameters, such as the expansion rate H_0 or the matter density Om, from the baryonic acoustic oscillations (BAO), the redshift space distortions (RSD) and the shape of the power spectrum broadband. In the second part I will present the implication of these measurements within the context of LCDM models and extensions and the impact with the current tensions in cosmology.

Cosmology with the Kilo Degree Survey

• Marika Asgari (Edinburgh U.)

Probes of the large scale structures can give us insight into the nature of the dark Universe. In this talk I will show the latest results from the Kilo Degree Survey (KiDS) and its combination with spectroscopic galaxy surveys. KiDS is a purpose-built gravitational lensing survey with high quality images and a wide photometric coverage, resulting in very high-fidelity data. Combining weak lensing data with other probes of the large scale structures, such as galaxy clustering, enables us to break degeneracies in cosmological parameters and control the systematics in the data. Finally, I will discuss the prospects for the KiDS final data release.

Reconstructed gravity and cosmological tensions

• Alessandra Silvestri (Instituut Lorentz (Leiden University))

I will discuss some recent works on reconstruction of gravity from a combination of currently available cosmological data , under conditions of theoretical stability, highlighting the imprints of cosmological tensions.

Current constraints on the curvature of the Universe

• Alessandro Melchiorri (Università di Roma Sapienza)

I will present the current observational status on the curvature of the Universe.

The Hubble tension and new physics at the eV scale The path to New Early Dark Energy

• Martin Sloth (CP3-Origins)

I will discuss the possibility that the Hubble tension is the signature of a fast triggered phase transition in the dark sector. Such a phase transition is called New Early Dark Energy (NEDE) and must have taken place just before recombination at the eV scale to resolve the tension fully. After discussing the cosmological NEDE phase transition, I will discuss the details of possible particle physics realizations.

3-forms as a mean of resolving tensions

• Mariam Bouhmadi López (University of the Basque Country & IKERBASQUE)

"In the current talk, I will present some dark energy models based on 3-forms that fully fit the available observational data. In addition, those models are harmless from a quantum point of view, in the sense that the singularities or abrupt events they might induce are cured at the quantum level. Moreover, some of those models can support regular blackholes as well as wormholes that do not require matter with a wrong kinetic term."

Resolving Dark Matter Tension: The impact of dynamical friction due to fuzzy dark matter on satellites with triaxial and logarithmic potentials

• Kostas Gourgouliatos

A possible candidate for dark matter is an ultralight bosonic particle comprising the Fuzzy Dark Matter (FDM). The presence of FDM in a galactic cluster will impact the motion of satellites residing in such clusters, through dynamical friction. Here we present numerical simulations of the dynamical friction on satellites traversing an initially uniform FDM halo. The potentials of the satellites we have studied are triaxial and logarithmic. We find that the wakes created on the FDM halo due to the passage of such satellites are qualitatively different from those generated by spherically symmetric systems and we quantify the impact of fuzzy dark matter on the dynamical friction coefficient of the satellites.

Explaining the Hubble tension and dark energy from alpha-attractors

• Konstantinos Dimopoulos (Lancaster University)

A compelling unified model of dark energy and early dark energy (EDE) is presented, using a scalar field with a simple exponential runaway potential, in the context of alpha-attractors. The field is originally trapped at an enhanced symmetry point, subsequently thaws to become successful EDE and eventually slow-rolls to become dark energy. EDE ameliorates the observed Hubble tension. Emphasis is put on concrete predictions of both EDE and dark energy to be tested in the near future.

Cosmology under the fractional calculus approach: a possible $H_0$ tension resolution?

• Genly Leon (Universidad Catolica del Norte)

Fractional cosmology has emerged recently, based on the formalism of fractional calculus, which modifies the standard derivative to one fractional derivative of order $\alpha$. It generates changes in General Relativity, particularly in the Einstein field equations. In this mathematical framework, the Friedmann equations are modified with an additional term similar to an effective curvature. The standard evolution of the cosmic species densities depends on the $\alpha$ fractional parameter and the age of the Universe $t_U$. The hypothesis is that the Universe does not contain a dark energy component. The late accelerated expansion can be sourced by the additional term in the new equation governing the cosmic dynamics. To elucidate that, we estimate stringent constraints on the fractional parameter using cosmic chronometers, Type Ia supernovae and joint analysis. We obtain $\alpha=2.839^{+0.117}_{-0.193}$ within one sigma confidence level that can provide a non-standard cosmic acceleration at late times; consequently, the Universe would be older than the standard estimations. Additionally, we present a dynamical system and stability analysis to explore the phase-space under the assumption of different $\alpha$ parameters. One late-time attractor, which is physical for $1 \leq \alpha < 5/2$, corresponds to a power-law (decelerated) late-time attractor for $\alpha < 2$. Moreover, an additional point not present in GR exists, which is physical for $\alpha > 1$ and a sink for $\alpha > 2$. This solution is a decelerated power-law if $1 < \alpha < 2$ and an accelerated power-law solution if $\alpha > 2$. This last result is consistent with the mean values obtained from the observational analysis. Therefore, under the fractional calculus, it is possible to obtain modified Friedmann equations at the background level, which provide a late cosmic acceleration without introducing a dark energy component. This radical approach could be a new path to tackle problems not resolved until now in cosmology. We analyse whether fractional cosmology can alleviate $H_0$ tension.

Solving tensions faster with velocities

• Miguel Quartin (Heidelberg U. + U. Federal do Rio de Janeiro)

Peculiar velocity surveys using supernovae or standard sirens can be combined with large-scale galaxy surveys to great benefit. I will present a new methodology to analyse in a comprehensive way standard candles and galaxy data at the linear level. I will show that this methodology also allows for competitive model-independent measurements of the expansion rate, i.e. without any assumptions on the cosmological model besides the FLRW metric. For supernovae, I will provide forecasts for future surveys like 4MOST, DESI and LSST, and show that this leads to increased precision in sigma8 and the growth rate compared to the traditional method using only galaxies. The measurements can have similar precision to those of the CMB but exhibit orthogonal degeneracies, and the combined constraints yield huge improvements in both cosmological background and perturbation parameters. For standard sirens observed with next-gen telescopes, similar precision can be achieved in sigma8 and the growth rate, but we can also get a very high precision of 0.1% in H0. This means that this methodology can help solve both the current H0 and sigma8 tensions.

Tensions in Cosmological Probes and Quasar Cosmology

• Micol Benetti (University of Naples)

In the current era of precision cosmology, the emergence of crucial tensions in the determination of the universe expansion has led to a twofold need to determine a criterion for combining different probes in a physically meaningful way, and to extend the mapping of the expansion of the universe to include data at redshifts not currently covered. In this talk, I will present recent compatibility estimates of cosmological data and illustrate the possibility of using Quasar as cosmological probes, which can extend the Hubble diagram of SNe to a higher redshift range (𝑧 = 2.4 - 7.5) in which the predictions of cosmological models can be distinguished. The LCDM model and some of its extensions and tensions are tested and possible incompatibility between BAO, SNe and QSO data are explored.

Update on GW standard siren cosmology

• Daniel Holz (University of Chicago)

The era of gravitational-wave cosmology has finally begun. The multi-messenger observations of GW170817 allowed it to be used as a standard siren, providing a direct measurement of the Hubble constant calibrated by the theory of general relativity. In addition to this "bright siren" approach, a "dark siren" approach has been implemented utilizing statistical correlations with host galaxies to constrain cosmological parameters. More recently, a "spectral siren" approach has been developed, which uses observed features in the statistical distribution of GW sources to constrain redshift and infer cosmology. We will summarize recent results and discuss future prospects.

Tensions and anomalies: how well do we understand subtle dependencies of galaxy clustering on their properties?

• Agnieszka Pollo (National Center for Nuclear Research)

Galaxies are known to be good although biased tracers of the underlying dark matter field. This bias, mostly driven by history of hierarchical clustering and galaxy/halo assembly history, results in the dependence of galaxy clustering on their physical properties which is not easy to model. On the other hand, making use of galaxies as tracers of cosmic structure for cosmological purposes strongly relies on our understanding of the relations between a galaxy, its DM halo and large-scale environment and its evolution. In my talk I will show some recent results from my group pointing to nontrivial dependencies between galaxy properties and their environment affecting clustering measurements, thus possibly contributing to some cosmic tensions, and pointing to the necessity of new generation of models and simulations.

Interacting vacuum and tensions

• Marco Bruni (University of Portsmouth)