Our understanding of the Universe is at a turning point with the predictions of the standard cosmological model and the observations from different surveys are showing tensions in several key areas. The disagreement is expressed in the value of cosmic expansion as well as in the growth of large-scale structure in the Universe. New cosmological surveys, many of which are European, may expose tension in additional areas of the concordance model. The question of cosmological tensions can be confronted in a number of ways. Firstly, survey data needs to be further analysed for potential systematic uncertainties or biases. Secondly, there have been numerous advances in approaches to data analysis and statistics, some of which provide less dependence on cosmological models to make cosmological parameter estimates. Lastly, there are a plethora of new proposals from fundamental physics which range from novel neutrino physics to dark energy proposals (and others) which may contribute to a solution to the cosmological tensions problem. These represent the three research themes through which cosmological tensions will either be alleviated or resolved.

**CosmoVerse@Krakow** is the second annual conference in a series of conferences that aim to establish a link between the different research areas in cosmology with the main focus on confronting the growing challenges of tensions in recent cosmological survey data. This conference is organized within the Cost action initiative CA21136 – Addressing observational tensions in cosmology with systematics and fundamental physics (CosmoVerse). Learn more about CosmoVerse action **here**.

**Main topics**

**Observational cosmology and Systematics**(cross-correlation of data, systematic effects)**Data analysis**(astrostatistics; data science in astronomy; Bayesian analysis; machine learning and artificial intelligence)**Fundamental Physics**(challenge of the cosmological hypothesis, dark energy and modified gravity, neutrino physics, dark energy, and dark matter interaction).

##### Venue

The conference took place in Kraków at Faculty of Physics, Astronomy and Applied Computer Science of the Jagiellonian University.

You can find more information on the indico webpage of the conference.

**Dates**

The conference took place **9 July – 11 July 2024**.

**Invited Speakers**

Stefano Anselmi, INFN, Sezione di Padova, Italy

Wendy Freedman, The University of Chicago, USA (online)

Ariel Goobar, Stockholm University, Sweden

Tanvi Karwal, Kavli Institute for Cosmological Physics, The University of Chicago, USA

Lloyd Knox, UC Davis, USA

Adam Riess, Johns Hopkins University, USA

Mairi Sakellariadou, King’s College London, UK

##### Best poster award

At each CosmoVerse conference, a vote is cast to grant an award to the best poster presented. This year, **Mrs. Wei-Ning Deng**, from Astrophysics Group, Cavendish Laboratory, Cambridge, won the Award for her poster entitled:

**“Theoretical Prediction of Curvature Ωκ: Based on Periodic Universe.”**

#### Sessions' talks

#### Plenary talks

###### Ozgur Akarsu

Recent theoretical and observational developments in LsCDM Cosmology: On track to a new concordance model

Sign-switching cosmological constant cold dark matter ($\Lambda_{\rm s}$CDM) cosmology has emerged as a compelling new paradigm, demonstrating unprecedented success in aligning with observational data from various datasets and effectively resolving major cosmological tensions. This model is characterized by a minimal deviation from the standard $\Lambda$CDM model, proposing a rapid Anti-de Sitter (AdS) to de Sitter (dS) transition in the late universe ($z_\dagger\sim 1.7$), inspired by the graduated dark energy (gDE) model. In this talk, we will first provide a concise introduction to $\Lambda_{\rm s}$CDM cosmology. We will then discuss the latest theoretical and observational developments that underscore $\Lambda_{\rm s}$CDM as a promising candidate or guide for a new concordance cosmological model of the Universe.

###### Lilia Anguelova

Multifield Cosmology and the Dark Universe

Multifield cosmology, arising from the interaction of multiple scalar fields with gravity, can lead to qualitatively new features, when the background solutions have strongly non-geodesic trajectories in field space. This is the so called rapid-turn regime. We outline the reasons why rapid-turning can produce novel effects relevant for inflation, dark matter or dark energy. Then we focus on a particular class of multifield dark energy models in the rapid-turn regime. We show that the speed of sound of the dark energy perturbations, in these models, is reduced compared to the speed of light, which can have implications for the large-scale clustering of matter. Furthermore, we argue that this class of models holds significant promise for alleviating the Hubble and $\sigma_8$ tensions simultaneously.

###### Jacobo Asorey Barreiro

Updating cosmological tensions using the most recent datasets from early and late Universe probes

In the recent years, with the improvement on the precision of the different cosmological probes, the rise of some of the tensions and anomalies that affect the standard model of cosmology, like the H0-tension, the sigma_8-tension and the lensing anomaly, has motivated the study of alternative models to the standard LCDM model in order to reconcile these tensions. In this talk, I will show some re-analysis of some of the most common extensions of LCDM with different combinations of the latest datasets such as Planck PR4, type Ia SN and the DESI BAO 2024, in order to see if it is possible to alleviate the tensions.

###### David Benisty

Constraining Dark Energy from Local Universe

In this talk I will develop a method to constrain the Cosmological Constant Λ from binary galaxies, focusing on the Milky Way and Andromeda. I will provide an analytical solution to the two-body problem with Λ and show that the ratio between the Keplerian period and TΛ = 2π/(c √ Λ) ≈ 63.2 Gyr controls the importance of effects from the Cosmological Constant. The Andromeda-Milky Way orbit has a period of ∼ 20 Gyr and so Dark Energy has to be taken into account. Using the current best mass estimates of the Milky Way and Andromeda galaxies, I find the Cosmological Constant value based only on the Local Group dynamics to be lower then 5.44 times the value obtained by Planck. With future astrometric measurements, the bound on the Cosmological Constant can be reduced to (1.67 ± 0.79) ΛPL. The results offer the prospects of constraints on Λ over very different scales than previously. With other binary systems I show that the upper bound on the cosmological constant decreases when the orbital period of the system increases, emphasizing that Λ is a critical period in binary motion.

based on Astrophys.J.Lett. 953 (2023) 1, L2

###### Clecio Bom

A dark standard siren measurement of the Hubble constant following LIGO/Virgo/KAGRA O4a and the Legacy Survey

We present a new constraint on the Hubble constant (H0) from the standard dark siren method using a sample of 5 well-covered gravitational wave (GW) alerts reported during the first part of the fourth LIGO/Virgo/KAGRA observing runs in combination with standard dark sirens from the first three runs. Our methodology relies on the galaxy catalog method alone. We use the full probability density estimation of photometric redshifts derived by a deep learning method using the DESI Legacy Survey and DELVE galaxy catalogs. We add the constraints from 5 new well-localized binary black hole mergers to the sample of standard dark sirens analyzed in Alfradique et al. (2024). We combine the H0 posterior for 5 new standard sirens with other 10 previous events (3 with updated posteriors), finding H0=69.9^{+13.3}_{−12.0} km s−1 Mpc−1 (68% Highest Density Interval) with the catalog method alone. This result represents an improvement of ∼23% comparing the new 15 dark siren constrain with the previous 10 dark siren constraint, and a reduction in uncertainty of ∼40% from the combination of 15 dark and bright sirens compared with the GW170817 bright siren alone. The combination of dark and bright siren GW170817 with recent jet constraints yields H0 of 68.0^{+4.3}_{−3.8} km s−1 Mpc−1, a ∼6% precision from Standard Sirens, reducing the previous constraint uncertainty by ∼10% .

###### Rebecca Briffa

Constraints on Tensor Perturbations from Cosmological Data Using Teleparallel Gravity

In this study, we explore novel observational constraints within the framework of $f(T)$ gravity, focusing on the impact of primordial gravitational waves on the Cosmic Microwave Background (CMB) anisotropies and the B-mode polarization spectrum. Our investigation incorporates a teleparallel formulation for the background cosmology, enabling us to extend our analysis to include late-time cosmological datasets such as the Hubble data, Pantheon plus data, and Baryon Acoustic Oscillations (BAO) data from the DESI collaboration. By integrating these diverse datasets, we obtain a more comprehensive understanding of tensor perturbations within the $f(T) $ framework. Additionally, our study sheds light on the behaviour of cosmological tensions within this framework at late-time epochs. This approach enhances our grasp of $f(T) $ gravity’s implications for the late-time universe, contributing to a deeper comprehension of its underlying dynamics.

###### I-Non Chiu

Cosmology from weak-lensing shear-selected galaxy clusters in the Hyper Suprime-Cam Subaru Strategic Program

We present cosmological constraints using the abundance of shear-selected galaxy clusters in the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The clusters are selected on the mass maps constructed using the three-year (Y3) weak-lensing data with an area of ≈ 500 deg2, resulting in a sample size of 129 clusters with a high signal-to-noise ratio 𝜈 of 𝜈 ≥ 4.7. Owing to the deep, wide-field, and uniform imaging of the HSC survey, this is by far the largest sample of shear-selected clusters, in which the selection solely depends on gravity and is free from any assumptions about the dynamical state. Informed by the optical counterparts, the shear-selected clusters span a redshift range of 𝑧 ≲ 0.7 with a median of 𝑧 ≈ 0.3. We carefully account for (1) the bias in the photometric redshift of sources, (2) the bias and scatter in the weak-lensing mass using a simulation-based calibration, and (3) the measurement uncertainty that is directly estimated on the mass maps. The results present the first cosmological constraints from the shear-selected clusters, paving a way forward for cluster cosmology in the future LSST era.

###### Luis Adrián Escamilla Torres

Model Independent reconstruction of an Interacting Dark Energy

In this talk I will explain what is a Model Independent reconstruction and how it can be used to study Dark Energy models, particularly in a scenario where Dark Energy can interact with Dark Matter.

###### William Giarè

Dark interactions in the Cosmic Microwave Background

According to the standard model of cosmology, about 95% of the energy density of the Universe is made up of Dark Matter (DM) and Dark Energy (DE). Given our limited understanding of these components, an intriguing idea is to consider interactions on cosmological scales. In this talk, I will show that interacting models offer an interesting perspective both from a theoretical and phenomenological standpoint. I will argue that several independent observations of the cosmic microwave background (CMB) seem to support an interacting dark sector, which can help address some cosmological tensions. Finally, I will point out that small-scale CMB observations can open a novel observational window to accurately test interactions, possibly revealing unique signatures challenging to detect on larger angular scales.

###### Benjamin Giblin

Slicing Through the Tension: The Future of Cosmological Weak Lensing

Cosmological information contained within the non-linear regime of the Universe may prove crucial in solving the tension currently observed between weak lensing and CMB probes. However, this information lies beyond the reach of our conventional analyses which use two-point statistics. In this talk, I present the improvements in cosmological constraining power offered by an alternative weak lensing statistic, the projected matter density PDF. For realistic lensing survey specifications, this statistic yields >50% improvements in the constraints on the matter energy density parameter, $Ω_m$, and the amplitude of the matter power spectrum, $σ_8$. We also find significantly improved precision for the Hubble parameter, $H_0$, and the dark energy equation of state parameter, $w_0$. I will demonstrate how these gains in cosmological constraining power can be made reality with tailored numerical simulations paired and machine learning.

###### Daniela Grandón

The impact of baryons on cosmological parameters from HSC Y1 non-Gaussian statistics

We present cosmological constraints derived from lensing peak counts, minimum counts, one-point PDF and the angular power spectrum of the Subaru Hyper Suprime-Cam first-year (HSC Y1) weak lensing shear catalog. These summary statistics contain non-

Gaussian information and hence are complementary to the conventional two-point statistics in constraining cosmology. In this

work, we forward-model the ‘non-Gaussian statistics’ and their dependence on cosmology, using a suite of 𝑁-body simulations

tailored to the HSC Y1 data. We also investigate the impact of baryons on the lensing non-Gaussian statistics and the resulting biases in the matter clustering amplitude S8 =σ8 sqrt(Ωm/0.3), when the smallest scales are included. We find up to 1σ bias in S8 when the smallest scales (2 arcmin) and the highest feedback level are considered. Our results indicate no tension between the S8 inferred from HSC

Y1 lensing and from CMB measurements, such as Planck 2018 and recent CMB lensing constraints from the Atacama Cosmology Telescope and the South Pole Telescope.

###### Lindita Hamolli

Detection of the lensed quasars by the Nancy Grace Roman Space Telescope

Strong gravitational lensing is a powerful tool for mapping the distribution of dark matter and testing various cosmological parameters. One such parameter is the Hubble Constant, which can be determined by measuring the time delay between lensed images. Our study focuses on the detection of lensed quasars by forthcoming Nancy Grace Roman Space Telescope (Roman) survey. Based on the capability of the Roman telescope and the recent results for the Quasar Luminosity Function (QLF) in the infrared band of Spitzer Space Telescope imaging survey, we find the number of quasars that will be observed by Roman telescope. Also, we develop Monte Carlo simulations using the mass-luminosity distribution function of galaxies and the redshift distributions of galaxies and quasars to find the efficiency that a quasar to be lensed by foreground galaxies. Even though this survey is not primarily designed as a strong lensing detection experiment, it will still provide a large complementary catalogue to forthcoming lensing discovery projects.

###### Will Handley

PolySwyft: a sequential simulation-based nested sampler

We present recent advances in combining Nested Sampling and Simulation Based Inference, and show these are performant for cosmological scale problems. Nested sampling [1,2] is a numerical Bayesian inference tool for performing model comparison and parameter estimation, and has been widely applied across cosmology & particle physics. Simulation based inference (SBI) is an emerging new paradigm for data analysis [3], which allows researchers to perform inference tasks such as parameter estimation, model comparison, and hypothesis testing directly from forward simulations without the need for an explicit likelihood function, and has already had successful application in weak lensing [4] and 21cm cosmology [5]. By removing the need for an explicit likelihood, SBI frees us from assumptions such as fiducial cosmological model (typically ΛCDM) and comprises a next-generation tool for disentangling tensions from systematics.

At its heart, the nested sampling meta-algorithm requires sampling from the prior subject to a hard likelihood constraint. It is therefore challenging to apply nested sampling if the likelihood is not explicitly available, as is the case in simulation based inference. To address this, we propose a sequential algorithm which iteratively runs nested sampling on a ratio estimator whose training data are progressively informed by the dead points of the previous nested sampling runs. This replaces truncation with nested sampling’s dead measure, and allows training of neural ratio estimators without marginalisation for generative models with around 10 free parameters without marginalisation.

As an example of this synthesis, we use PolyChord [6] for nested sampling and swyft [7] for the neural ratio estimator (forming PolySwyft), but emphasise the generality of this approach throughout. We showcase it on CMB and 21cm toy examples, and discuss potential future extensions to higher numbers of parameters and a deeper integration of the two algorithms.

[1] https://arxiv.org/abs/2205.15570

[2] https://arxiv.org/abs/2101.09675

[3] https://arxiv.org/abs/1911.01429

[4] https://arxiv.org/abs/2403.02314

[5] https://arxiv.org/abs/2403.14618

[6] https://github.com/PolyChord/PolyChordLite

[7] https://swyft.readthedocs.io/en/stable/

###### Wojciech Hellwing

Breaking the cosmic degeneracies with non-standard probes

Classical LSS probes of growth rate/gravity relies on clustering statistics, RSD and lensing. Most observables related to those techniques suffer from various biases and degeneracies. To the most severe problems include: theoretical bias related to the way how the signal is modelled and extracted and baryonic effects leading to degeneracy of the clustering strength signal with the efficiency of various galaxy formation processes.

I will discuss some non-standard probes (including peculiar velocities and clustering amplitudes) and their combination that can be used for cross-correlating with standard probes to estimate the unknown systematic errors. This opens an avenue to mitigate mentioned problems and used better accuracy for cosmological constraints on gravity and the growth-rate. Using non-standard probes offers also an unique way for a cosmology self-consistency test of the current data sets. Such tests can significantly help in hunting of unknown systematics – a crucial topic in the context of existing observational tensions in the LCDM (like S8 and H0 tensions).

###### Mariana Jaber Bravo

A dark matter solution to the H0 and S8 tensions, and the integrated Sachs-Wolfe void anomaly

We consider a phenomenological model of dark matter with an equation-of-state that is negative and changing at late times. We show that this couples the $H_{0}$ and $\sigma_8$ tensions, providing an explanation for both simultaneously, while also providing an explanation for the anomalously large integrated Sachs-Wolfe (ISW) effect from cosmic voids. Observations of high ISW from cosmic voids may therefore be evidence that dark matter plays a significant role in the $H_{0}$ and$\sigma_8$ tensions. We predict the ISW from cosmic voids to be a factor of $\sim2$ greater in this model than what is expected from the standard model $\Lambda$CDM.

###### Nihan Katırcı

Unexplored regions in teleparallel gravity: Sign-changing dark energy density

In this talk, we will discuss construction of $\Lambda_{\rm s}$CDM-type cosmologies within teleparallel gravity, $f(T)$ gravity to address major cosmological tensions such as $H_0$ and $S_8$ tensions.

###### Aleksander Lenart

Cosmology in the Realm of Gamma-Ray Bursts and Quasars

Despite decades of research, cosmology still lacks reliable probes to study the Universe in the intermediate redshift regime (from z = 1 up to z = 1100). Very few astronomical objects observed at such high distances can be standardized. We present the case of two such sources: Gamma-Ray Bursts (GRBs, $z<9.4$) and Quasars (QSOs, $z<7.4$). For GRBs, the observational luminosity distance can be derived using an empirical log-linear relation between the luminosity at the end of the plateau phase ($L_{a}$), rest-frame time at the end of the plateau ($T^{*}_{a}$), and luminosity during the peak phase ($L_{peak}$). This relation was first formulated by Dainotti et al. (2016) as $\log_{10}L_{a} = a\times \log_{10}T^{*}_{a} + b\times \log_{10}L_{peak} +c$.

QSOs, on the other hand, follow a power-law correlation between the luminosity observed in the X-ray band ($L_{X}$) and the optical luminosity ($L_{UV}$). This correlation was presented by Risaliti & Lusso (2015) as $L_{X}=\beta \times L^{\gamma}_{UV}$. Although these correlations have been shown to result from the intrinsic physics of the sources rather than observational effects, applying them to cosmological computations remains challenging. A reliable fitting method must properly take into account selection bias and redshift evolution. We demonstrate that samples of GRBs and QSOs are significantly affected by these effects. Additionally, we present a circularity-free method for fitting the cosmological model based on a de-evolving procedure developed by Efron & Petrosian (1992). Lastly, we present our results of fitting cosmological parameters.

###### Geraint Lewis

Is the cosmological principle in trouble?

I will present our recent results exploring the integrity of the cosmological principle, the idea that, on sufficient scales, the universe is homogeneous and isotropic. Recent tensions have arisen between the dipole of cosmological sources and its interpretation from the CMB as a kinematic departure from the local Hubble Flow, bringing the cosmological principle into doubt. With a Bayesian-based approach, I explore the cosmological dipole in optical/IR catalogues of quasars, using Bayesian evidence to assess differing hypotheses. The conclusion is, that whilst the picture is not completely clear, the results support the veracity of the cosmological principle.

###### Siyang Li

Reconnaissance with JWST of the J-region Asymptotic Giant Branch in Distance Ladder Galaxies: From Irregular Luminosity Functions to Approximation of the Hubble Constant

We study stars in the J-regions of the asymptotic giant branch (JAGB) of near-infrared color magnitude diagrams in the maser host NGC 4258 and 4 hosts of 6 Type~Ia~supernovae (SN~Ia): NGC 1448, NGC 1559, NGC 5584, and NGC 5643. These clumps of stars are readily apparent near $1.0<F150W-F277W<1.5$ and $m_{F150W}$=22-25~mag with \textit{James Webb Space Telescope} NIRCam photometry. Various methods have been proposed to assign an apparent reference magnitude for this recently proposed standard candle, including the mode, median, sigma-clipped mean or a modeled luminosity function parameter. We test the consistency of these by measuring intra-host variations, finding differences of up to $\sim$0.2~mag that significantly exceed statistical uncertainties. Brightness differences appear intrinsic, and are further amplified by the non-uniform shape of the JAGB luminosity function, also apparent in the LMC and SMC. We follow a “many methods’ approach to consistently measure JAGB magnitudes and distances to the SN~Ia host sample calibrated by NGC 4258. We find broad agreement with distances measured from Cepheids, tip of the red giant branch (TRGB), and Miras. However, the SN host mean distance estimated via the JAGB method necessary to estimate $H_0$ differs by $\sim$0.19~mag amongst the above definitions, a result of different levels of luminosity function asymmetry. The methods yield a full range of $71-78$ km s$^{-1}$ Mpc$^{-1}$, i.e., a fiducial result of $H_0=74.7\pm2.1$(stat)$\pm$2.3(sys)($\pm$3.1 if combined in quadrature) km s$^{-1}$ Mpc$^{-1}$, with systematic errors limited by the differences in methods. Future work may seek to further standardize and refine this promising tool, making it more competitive with established distance indicators.

###### Upala Mukhopadhyay

Dark energy in light of the early JWST observations: indicating a negative cosmological constant?

Early data from the James Webb Space Telescope (JWST) has uncovered the

existence of a surprisingly abundant population of very massive galaxies at extremely high redshift, which are hard to accommodate within the standard ΛCDM cosmology. We explore whether the JWST observations may be pointing towards more complex dynamics in the dark energy (DE) sector. Motivated by the ubiquity of anti-de Sitter vacua in string theory, we consider a DE sector consists of a negative cosmological constant (nCC) and a evolving component with positive energy density on top, whose equation of state is allowed to cross the phantom divide. We show that such a scenario can drastically alter the growth of structure compared to ΛCDM, and accommodate the otherwise puzzling JWST observations if the dynamical component evolves from the quintessence-like regime in the past to the phantom regime today: in particular, we demonstrate that the presence of a nCC (which requires a higher density for the evolving component) plays a crucial role in enhancing the predicted cumulative comoving stellar mass density. Our work reinforces the enormous potential held by observations of the abundance of high-z galaxies in probing cosmological models and new fundamental physics, including string-inspired ingredients.

###### Leandros Perivolaropoulos

Hubble tension and its redshift tomography

I will review the essence of the Hubble tension, its current observational status and the three classes of theoretical models that attempt to address it. Then I will focus on the level of the tension in redshift bins as expressed by the mismatch between distances measured by BAO data and by SnIa data calibrated respectively by the CMB sound horizon scale and by the Cepheid based distance ladder. The variation of the tension with redshift will be discussed and its possible implications for theoretical models will be analysed.I will review the essence of the Hubble tension, its current observational status and the three classes of theoretical models that attempt to address it. Then I will focus on the level of the tension in redshift bins as expressed by the mismatch between distances measured by BAO data and by SnIa data calibrated respectively by the CMB sound horizon scale and by the Cepheid based distance ladder. The variation of the tension with redshift will be discussed and its possible implications for theoretical models will be analysed.

###### Ruchika

BAO Anomalies after DESI Release

In the era of tensions, when precision cosmology is blooming, numerous new theoretical models are emerging. However, it’s crucial to pause and question the extent to which the observational data we rely on are model-dependent. In this work, we study the comoving position of the acoustic peak, a cornerstone standard ruler in cosmology. We considered BAO observational datasets from two distinct teams and calculated $r_d$ sound horizon value with the help of each BAO data set along with SN I-a data from the Pantheon Plus sample. Our conclusion at present is there is a significant amount of tension within two independent BAO datasets. We further go on to say that while one BAO data set allows solutions like Early Dark Energy, the other completely rules out $r_d$ tension and hence the possibility of early modifications of $r_d$ such as EDE as a solution to Hubble Tension.

###### Matilde Signorini

Distance measurements with Active Galactic Nuclei

Measuring cosmic distances accurately is a critical challenge in astrophysics, pivotal for our understanding of the Universe expansion history and for testing cosmological models. In this talk, I will explore two innovative methods for using Active Galactic Nuclei (AGN) as tools for distance measurement. AGN, notable for their extreme luminosity, can be observed even at high redshifts; however, their variable emission precludes straightforward distance estimations based on flux measurements alone. I will describe two techniques developed to standardize AGN and use them for distances. Firstly, I will examine the X-ray – UV luminosity relation in quasars—the most luminous types of AGN. I will discuss recent advancements in enhancing the reliability and precision of distance estimates obtained with this relation and how they challenge the standard ΛCDM cosmological model’s predictions when implemented with SNe in the Hubble Diagram. Secondly, I will explore the correlation between AGN X-ray variability and black hole mass, utilizing the BASS dataset at low redshifts to characterize it. Additionally, I will discuss the potential impacts of forthcoming data from the Euclid, LSST, and Athena missions.

###### Enrico Specogna

Breaking planck’s lensing anomaly: a parametric approach

Parametrising the growth of large scale structure is a powerful tool, as it allows us to detect deviations from the Standard Model of cosmology – SM in a general way, without having to make limiting assumptions about their fundamental nature. We will be presenting the results of a series of analyses carried on two such parametrisations: the growth index – ‘$\gamma$’, a precise modification of the growth of linear, sub-horizon matter perturbations in the SM, and the ‘$\mu_0$ − $\Sigma_0$’ framework, a modification of the Poisson and lensing equations from General Relativity – GR. Notably, Planck’s 2018 analysis has shown a $2\sigma$ evidence of Modified Gravity – MG (i.e., $\mu_0$, $\Sigma_0 \neq 0$), while other Cosmic Microwave Background – CMB experiments such as ACT and SPT showed consistency with GR. Could Planck’s lensing anomaly be responsible for this? The goal of our work is to show if the link between the loss of power at high multipoles in the anisotropy power spectra of Planck and the detected evidence for MG stands the test of alternative approaches to analyse Planck’s data, as the one taken by the HiLLiPoP team who, consistently with other CMB experiments, have found no sign of abnormal lensing signals. We find that the usage of the HiLLiPoP likelihood on Planck data does not reveal any deviation from the SM, suggesting that the lensing anomaly could plausibly explain the MG detection by Planck.

###### Denitsa Staicova

Marginalization approach in Baryonic Acoustic Oscillation – what we have learned so far?

Baryonic Acoustic Oscillations (BAO), with their intrinsic connection to the physics of both the early and late universe, offer a great opportunity to gain insights into the Hubble tension. This talk will summarize recent results obtained by analyzing BAO datasets. We will discuss the challenges in using BAO, particularly the degeneracy between the Hubble constant (H_0) and the sound horizon (r_d) and we will then present our marginalization technique to overcome this problem. We will discuss the results from the application of this method in constraining different dark energy models, including our most recent work dedicated to the interacting dark energy (IDE).

###### Elsa Teixeira

An interacting dark sector from fluid approximations

The persistent discrepancy between theoretical predictions of the standard cosmological model and precision measurements from diverse observational probes remains a pressing challenge in modern cosmology. Over the past decade, mounting evidence for persistent discrepancies in the inferred values of cosmological parameters derived from both model-dependent and -independent methodologies has motivated the proposal of alternatives to the standard paradigm. In this seminar, I will focus on the exploration of potential missing physics within the standard model, focusing on the enigmatic dark sector comprising dark matter and dark energy, and any potential interactions between them. Leveraging on fluid approximations for the physical nature of the dark sector and its underlying dynamics, we assess the viability of various models in reconciling the observed cosmological tensions.

###### Sebastian Trojanowski

New insights on neutrino interactions with dark matter from CMB data

In the talk, I will revisit the possibility of using cosmological observations to constrain models that involve interactions between neutrinos and dark matter. I will show that small-scale measurements of the cosmic microwave background with a few percent accuracy are critical to uncovering unique signatures from models with small couplings that would require a much higher sensitivity at lower multipoles. In order to test this, the currently available high-multipole data have been analyzed, both independently and in combination with low-multipole CMB and Baryon Acoustic Oscillation measurements, finding a preference for a non-vanishing coupling at 68% CL. This aligns with other CMB-independent probes, such as Lyman-α. I will illustrate how this coupling could be accounted for in dark matter interactions with a sterile neutrino.

###### J. Alberto Vazquez

Deep Learning and genetic algorithms for cosmological Bayesian inference speed-up

In this talk, we present a novel approach to accelerate the Bayesian inference process, focusing specifically on the nested sampling algorithms. Our method utilizes the power of deep learning, employing feedforward neural networks to approximate the likelihood function dynamically during the Bayesian inference process. Unlike traditional approaches, our method trains neural networks on-the-fly using the current set of live points as training data, without the need for pre-training. This flexibility enables adaptation to various theoretical models and datasets. We perform the hyperparameter optimization using genetic algorithms to suggest the initial neural network architectures for learning each likelihood function. Once sufficient accuracy is achieved, the neural network replaces the original likelihood function.

###### Maximilian von Wietersheim-Kramsta

KiDS-SBI: Simulation-Based Inference Analysis of KiDS-1000 Cosmic Shear

Cosmic shear, the weak gravitational lensing effect on distant galaxies due to matter in the foreground, is a powerful tool to study the distribution of matter, to probe its large-scale structure, and infer the cosmological model of the Universe. Standard analyses are typically based on the assumption of a Gaussian likelihood with a parameter-independent covariance, but these assumptions may not hold for all observables, scales and/or all systematics. Simulation-based inference (SBI) addresses this by evaluating an effective likelihood from forward-simulations which map parameters to data vectors. To this end, I will present a novel application of SBI to a cosmic shear analysis of the Kilo-Degree Survey’s KiDS-1000 data release. The forward model is based on lognormal random fields which take into consideration systematics which are typically not modelled in standard inference, such as variable depth, point-spread function variations, shear biases, etc. I will also describe how the simulated galaxy catalogues are compressed to shear-shear angular two-point statistics which are further compressed using score compression. I will show how we train a 12-dimensional neural likelihood estimation to obtain a converged and unbiased posterior of the cosmological parameters within $\Lambda$CDM. We achieve this with only 10,000 model evaluations which run in a time comparable to a standard MCMC. We find that our constraints on the weak lensing parameter, $S_8$, are similar to constraints from previous analyses of KiDS-1000. We note a non-negligible parameter-dependence in the learnt likelihood which is consistent with cosmic variance. At the same time, we find that systematics such as variable depth can have significant impacts on the posterior estimates. Lastly, I will highlight how these findings and SBI will help address the modelling/inference challenges facing upcoming stage IV galaxy surveys.

###### Deng Wang

Lighting Dark Ages with ISW Effect

The integrated Sachs-Wolfe effect (ISW) describes how CMB photons pick up a net blue or redshift when traversing the time-varying gravitational potentials between the last scattering surface and us. Deviations from its standard amplitude could hint new physics. We show that reconstructing the amplitude of the ISW effect as a function of the redshift may provide a unique tool to probe the gravity sector during the era of dark ages, inaccessible via other cosmological observables. Exploiting Planck CMB temperature, polarization and lensing observations, we find a $2\sigma$ deviation from the standard ISW amplitude at redshift $z=500$. Barrying a systematic origin, our findings could point to either possibly new physics or a departure from the standard picture of structure formation under the General Relativity framework. Assuming the simplest two-redshift-bin scenario, we ensure $38\sigma$ and $2\sigma$ evidences of the early and late ISW effects, respectively, despite a priori possible degeneracy with the CMB lensing amplitude. Using a multiple tomographic method, we present the first complete characterization of the ISW effect over $k$-space and time. Future tomographic ISW analyses are therefore crucial to probe the dark ages at redshifts otherwise unreachable via other probes.

**SOC**

Jackson Levi Said (University of Malta, MT)

Eleonora Di Valentino (Sheffield University, UK)

Noemi Frusciante (UNINA, IT)

Agnieszka Pollo (National Center for Nuclear Research, PL)

Radoslaw Wojtak (Niels Bohr Institute Dark, DK )

**LOC**

Mateusz Rałowski (Astronomical Observatory of Jagiellonian University)

Anna Wójtowicz (Faculty of Science of Masaryk University)

Dominika Król (Astronomical Observatory of Jagiellonian University)

Adam Zychowicz (Astronomical Observatory of Jagiellonian University)

Aditya Narendra (Astronomical Observatory of Jagiellonian University)

Syed Naqvi (Astronomical Observatory of Jagiellonian University)

Arpita Misra (Astronomical Observatory of Jagiellonian University)

Subhrata Dey (Astronomical Observatory of Jagiellonian University)