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Tensions in Cosmology 2025
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Mon-Repos, Corfu, Greece
Mon-Repos, Corfu, Greece
Description
For registration click here: https://www.physics.ntua.gr/corfu2025/registration.html
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17:00
REGISTRATION
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17:00
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08:00
REGISTRATION
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1
OpeningSpeakers: Prof. Eleonora Di Valentino (University of Sheffield), Prof. Emmanuel Saridakis (National Observatory of Athens), Prof. Jackson Levi Said (Malta U.)
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2
The Hubble tension -- an overview and breakdown
The Hubble tension has reached the 5$\sigma$ confidence threshold and is currently considered the biggest crisis for the LCDM standard model of cosmology. Yet, despite more than a decade of thorough search, a well motivated and simple solution to the Hubble tension has not emerged. In this talk I review the current observational status of the Hubble tension and what makes the problem of trying to ease it with a new cosmological model so tricky. In particular, I focus on early and late universe cosmological probes and the possible avenues of systematic failure in their determination of the Hubble constant. Then, I give a short overview of the roads that are taken towards easing the tension through new theoretical models and the general lessons that can be gleamed from those studies.
Speaker: Prof. Nils Schöneberg (ICC, Barcelona U.) -
3
Scalar field models for the dark sector and cosmological tensions
The LCDM model relies on DM (described as a pressure-less fluid) and the cosmological constant. The physics of the dark sector is otherwise not specified. In this talk I discuss models in which the dark sector consists of (at least) two scalar fields, one of which a dark matter candidate, while the other plays the role of dark energy. These fields are interacting, resulting in theories with DM/DE interaction. I will discuss the cosmological implications of such models and their ability to address the cosmological tensions.
Speaker: Prof. Carsten van de Bruck (Sheffield U.) -
4
Statistical Nuances in BAO Analysis Likelihood Formulations and Non-Gaussianities
In this talk, we will present a systematic comparison of statistical approaches to Baryon Acoustic Oscillation (BAO) analysis using DESI DR2 data. We evaluate different methods for handling the nuisance parameter such as marginalization, profiling, Taylor expansion, and full likelihood analysis across multiple cosmological models. We demonstrate the how different cosmological models are constrained trough the different likelihoods. We will also discuss the use of eigenvalue decomposition of Fisher matrices to identify extreme parameter degeneracies in the different cosmological models, the information content and also the deviations from Gaussianity. Our analysis aims to demonstrate the importance of careful statistical treatment when extracting cosmological constraints from increasingly precise measurements.
Speaker: Prof. Denitsa Staicova (INRNE, BAS) -
5
Condensate Inflation in Chern-Simons Gravity and Running Vacuum Cosmology
I review a model of (metastable) approximately de-Sitter inflation induced by a condensate of chiral primordial gravitational waves in the early Universe in string-inspired Chern-Simons cosmologies, with gravitational anomalies. The model maps to a running vacuum model cosmology, and has the capability of alleviating the modern era cosmological tension under some natural assumptions.
Speaker: Prof. Nick Mavromatos (NTUA) -
11:10
Coffee Break
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6
Four forms and the cosmological constant problem
The cosmological constant problem remains one of the deepest puzzles in effective field theory and cosmology. In this talk, I will show how four-form field strengths offer model builders a valuable tool to tackle this challenge. I begin by reframing the problem using the infinite-wavelength (spacetime-averaged) trace of the gravitational equations. I then review and explore two main directions: first, how four-forms can make the cosmological constant dynamically adjustable, how charged membranes scan a landscape of vacua, and whether this requires anthropic selection or could instead follow from probabilistic dynamics. In the second part, I discuss a different role for four-forms in vacuum energy sequestering and present new ideas for embedding this and related mechanisms in higher-dimensional constructions.
Speaker: Prof. Antonio Padilla (Nottingham U.) -
7
Primordial black holes as cosmic expansion accelerators
We propose a novel and natural mechanism for cosmic acceleration driven by primordial black holes (PBHs) exhibiting repulsive behavior. Using a new ``Swiss Cheese'' cosmological approach, we demonstrate that this cosmic acceleration mechanism is a general phenomenon by examining three regular black hole spacetimes - namely the Hayward, Bardeen and Dymnikova spacetimes - as well as the singular de Sitter-Schwarzschild spacetime. Interestingly, by matching these black hole spacetimes with an isotropic and homogeneous expanding Universe, we obtain a phase of cosmic acceleration that ends at an energy scale characteristic to the black hole parameters or due to black hole evaporation. This cosmic acceleration mechanism can be relevant either to an inflationary phase with a graceful exit and reheating or to an early dark energy type of contribution pertinent to the Hubble tension. Remarkably, we find that ultra-light PBHs with masses $m<5\times 10^8\mathrm{g}$ dominating the energy content of the Univese before Big Bang Nucleosynthesis, can drive a successful inflationary expansion era without the use of an inflaton field. Additionally, PBHs with masses $m \sim 10^{12}\mathrm{g}$ and abundances $0.107 < \Omega^\mathrm{eq}_\mathrm{PBH}< 0.5$, slightly before matter-radiation equality, can produce a substantial amount of early dark energy, helping to alleviate the $H_0$ tension.
Speaker: Dr Theodoros Papanikolaou (Scuola Superiore Meridionale) -
8
Assessing the significance of CMB anomalies with cosmological gravitational waves
Since the very first observations, the Cosmic Microwave Background (CMB) has revealed on large scales unexpected features known as anomalies, which challenge the standard Λ cold dark matter (ΛCDM) cosmological model. One of these is the hemispherical power asymmetry, i.e. a difference in the average power on the two hemispheres centered around (l, b) = (221, −20), which shows a relatively high level of significance. Another is the lack-of-correlation, where the measured two-point angular correlation function of CMB temperature anisotropies is compatible with zero, differently from the predictions of the standard model. These anomalies could indicate a deviation from the standard model, unknown systematics, or simply a rare realization of the model itself. In this talk, I will investigate the physical origin of these anomalies, leveraging the potential information provided by the cosmological gravitational wave background (CGWB) detectable by future gravitational wave (GW) interferometers. In particular, I will analyze both constrained and unconstrained realizations of the CGWB to study the extent of information that GWs can offer. Indeed, the CGWB represents a unique window to explore the early universe and I will show that it can be used in combination with CMB data to shed light on the CMB anomalies.
Speaker: Dr Giacomo Galloni (University of Ferrara) -
9
A late Universe exact solution of GR to solve the cosmological tensions the Szekeres model
The tensions and anomalies appearing or increasing in the era of precision cosmology are due to a mismatch between the late time predictions obtained by applying the standard LCDM model (and its perturbations) to measurements at the CMB and actual measurements realized in our vicinity. Two main solutions to this issue can be considered: modifying Einstein's GR or keeping this theory and trying new ideas developped in its framework. Since the numerous tests of GR, realized both in the weak and strong regimes, have been positive thus far, we choose to work within this gravity theory. The Szekeres model will be our tool, owing to its following nice features: it is an exact solution of the field equations with a pressureless fluid (dust) as its gravitational source, exhibiting no symmetries (no Killing vectors) and having FLRW as a homogeneous limit. It is therefore well designed to reproduce any matter dominated region of the Universe. Here, we describe this solution and we show how its parameters can be constrained by the different experiments currently designed or by new observations to be scheduled in the future.
Speaker: Prof. Marie-Noelle Celerier (Paris Observatory) -
10
Exploring Cosmic Acceleration: Scalar Fields, Three-Forms, and the Sign Switching of the Cosmological Constant
We are currently living through a remarkable era in cosmology and gravitational physics, characterised by an unprecedented influx of observational data. One of the most pressing challenges facing cosmologists today is to understand the mysterious cause of the Universe’s recent accelerated expansion. The leading explanations for this phenomenon involve either a dark energy component or modifications to general relativity. In this talk, we will present a range of dark energy models, including axion-like scalar fields, three-form fields, and a sign-switching cosmological constant. We will also discuss the observational constraints on these scenarios and assess their potential to shed light on the ongoing H_0 and S_8 tension.
Speaker: Prof. Mariam Bouhmadi Lopez (Ikerbasque-EHU) -
13:20
Lunch Break
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11
Modified Friedmann Equations from Quantum Lattice Gravity: Implications for Cosmic Acceleration and the Hubble Tension
We propose a quantum gravity theory that leads to a modified Friedmann equation, potentially explaining the accelerated expansion of the universe without the need for dark energy. In our approach, cosmic acceleration arises naturally from quantum gravitational effects. The resulting corrections offer a possible resolution to the Hubble Tension by modifying both early and late-time cosmic evolution. We also explore the key predictions of this framework. Our results suggest that quantum gravitational effects could play a crucial role in addressing fundamental challenges in modern cosmology.
Speaker: Prof. Yoshiyuki Watabiki (Institute of Science Tokyo) -
12
Quasars as standard candles
A remarkable observational property of optically selected, blue quasars is the tight non-linear relation between their X-ray and UV emission. Since no complete physical model is available to explain such relation, a reliable derivation of distances based on its non-linearity requires a complete and careful analysis of the sample properties, in order to rule out systematic effects such as (a) a physical redshift evolution of the relation, (b) sample selection biases, (c) incorrect flux measurements (for example, due to dust extinction). I present the latest results on this project, in particular showing that the X-ray and optical-UV properties of our sample do no show any redshift dependence, and that all the observed dispersion of the relation is explained by residual "external" effects, such as the distribution of disk inclinations and variability. Finally, I show that the observational analysis of this relation is the only way to test its reliability, while any method involving statistical fits and/or comparisons with cosmological models is intrinsically flawed.
Speaker: Prof. Guido Risaliti (Florence U) -
13
Beyond the Standard Candle Cosmology with Quasars
I introduce quasars as new cosmological probes, leveraging the UVâX-ray luminosity relation and the Lusso & Risaliti catalog to build an extended Hubble diagram up to zâ¼7. I present joint analyses with several crucial probes as SNe Ia, BAO, DES, and CMB to test ÎCDM and dark energy models. The results show that simple model extensions fail to resolve current tensions, while interacting dark sector scenarios show improved consistency. This highlights the key role of quasars in bridging the gap between late and early-Universe observations.
Speaker: Prof. Micol Benetti (Scuola Superiore Meridionale, Federico II University) -
14
Reconstructing the matter power spectrum with cosmic shear
In this talk, I will present a method to directly reconstruct the matter power spectrum from linear to non-linear scales with cosmic shear. I will demonstrate that future cosmic shear surveys will be sensitive to the shape of the matter power spectrum on non-linear scales. I will show that it should be possible to distinguish between different models of baryonic feedback, and help provide a definitive answer to the question of whether weak lensing measurements on linear scales are consistent with the Planck ÎCDM cosmology. In addition, I will highlight how power spectrum reconstructions may lead to new discoveries on the composition of the dark sector, and discuss the possible degeneracies between axion and baryonic physics.
Speaker: Prof. Calvin Preston (University of Cambridge) -
15
Robust cosmology through combined probes
As wide-field surveys yield increasingly precise data, multiprobe analyses offer significant advantages. In this talk, I will discuss our recent study in which we use a previously developed framework to analyze combinations of three CMB (Planck PR3, Planck PR4, and ACT+WMAP) datasets, DESI Y1 Baryon Acoustic Oscillation (BAO) data, and a 9 Ã 2pt low-z dataset comprising KiDS-1000, BOSS DR12, and Planck CMB lensing/Integrated Sachs Wolfe (including all cross-correlations). I will discuss the internal consistency of and the hints of possible systematic effects in these data. Then I will show our associated constraints in ÎCDM and, motivated by recent DESI results, dynamical dark energy (w0waCDM) and free neutrino mass extensions. Finally, I will discuss the implications of these results in the context of recent cosmological hints of a dynamical dark energy scenario and (unphysical) negative neutrino masses. I will also touch on our ongoing work to further this analysis with data from DESI legacy imaging photometric clustering data. Based on https //arxiv.org/abs/2502.01722 and Reeves et al. in prep.
Speaker: Prof. Alexander Reeves (ETHZ) -
17:20
Coffee Break
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16
Advances in $\Lambda_{\rm s}$CDM Cosmology: Towards Resolving Multiple Cosmological Tensions
The sign-switching cosmological constant cold dark matter ($\Lambda_{\rm s}$CDM) cosmology has emerged as a promising new paradigm, showing notable success in reconciling observational data from diverse probes and in addressing major cosmological tensions, such as the $H_0$, $S_8$, and $\gamma$ (growth index) discrepancies. The model introduces a minimal but non-trivial modification to the standard $\Lambda$CDM framework by positing a rapid Anti-de Sitter (AdS) to de Sitter (dS) transition in the late universe ($z_\dagger \sim 1.7$), as originally conjectured in the context of graduated dark energy (gDE). The talk will begin with a concise review of $\Lambda_{\rm s}$CDM cosmology, followed by a presentation of recent theoretical and observational developments that highlight its potential role as a candidate framework guiding the search for a renewed concordance cosmology.
Speaker: Prof. Ozgur Akarsu (Istanbul Technical University) -
17
A field theoretic approach to resolving cosmological tensions including DESI DR2 data
One of the important challenges in modern cosmology relates to the search for models that go beyond $\Lambda$CDM for the resolution of cosmological tensions and lead to deviations from the standard model predictions. We discuss a field theoretic approach based on a dynamical quintessence field interacting with dark matter (QCDM) which can be utilized in the analysis of Hubble tension, $\sigma_8$ and as well as determine the state of state for dark energy. In the talk we will discuss QCDM based models to determine the dark energy EoS and the resulting phenomenology. Two distinct regions are identified where the equation of state behaves differently depending on the size of the dark matter-dark energy interaction strength. We show that the strong coupling region induces a transmutation of quintessence from thawing to freezing. Using the recent data release from the Dark Energy Spectroscopic Instrument (DESI), we rule out this possibility of transmutation and investigate the weak coupling region to derive upper limits on the interaction strength. We show that the interacting dark energy model is able to explain DESI's results without the equation of state crossing the phantom divide.
Speaker: Prof. Pran Nath (Northeastern University) -
18
New generation of calibrated TRGB modelsSpeaker: Dr Ippocratis Saltas (CEICO - Institute of Physics, Prague)
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19
Cosmic-Flows : Mapping galaxy motions to uncover fsigma_8 and H0
I will present research focused on measuring the peculiar (gravitational) velocities of galaxies. The goal is to achieve a three-dimensional reconstruction of the velocity field of the Local Universe, which reflects the distribution of both dark and luminous matter. This approach enables us to determine local values of fsigma_8 , H0 , and the local bulk flow, using these as key tests of the ΛCDM model and the underlying theory of dark matter. In addition, this work has allowed us to identify superclusters as basins of gravitation — including Laniakea, the supercluster in which we reside, and its five nearest neighboring superclusters.
Speaker: Prof. Helene Courtois (University Lyon 1) -
20
Primordial regular black holes as all the dark matter
I present a trilogy of works exploring the possibility that primordial black holes often considered as dark matter candidates, are non-singular objects. The investigations are motivated by the expectation that a complete theory of quantum gravity should ultimately resolve curvature singularitiesâan endemic feature of the Schwarzschild and Kerr metrics typically used to describe PBHs. In the first two studies, six phenomenological regular space-times were consideredâboth tr-symmetric and non-tr-symmetricâincluding well-known cases such as Bardeen and Hayward, as well as more recent metrics inspired by loop quantum gravity, such as the DâAmbrosio-Rovelli and Peltola-Kunstatter constructions. In all cases, the modified evaporation properties of non-singular PBHs were characterized and constraints on their abundance from γ-ray observations were derived. Compared to the Schwarzschild case, these metrics generally lead to weakened constraints on the PBH fraction of dark matter, enlarging the asteroid mass window where PBHs can account for all the DM. In the final work, moving beyond effective metrics, PBHs described by the covariant, quantum-corrected space-time proposed by Zhang, Lewandowski, Ma & Yang (ZLMY), were studied. ZLMY PBHs exhibit higher temperatures and no Cauchy horizons, leading to stronger evaporation constraints that partially reverse the previous trend, while relying on a more robust theoretical foundation. Together, this trilogy offers a proof-of-principle that quantum gravity-inspired regular space-times can significantly alter PBH phenomenology and open upâor constrainânew avenues for them to constitute the entirety of DM, highlighting the rich interplay between singularity resolution and cosmological observations.
Speaker: Prof. Davide Pedrotti (TIFPA-INFN, Universita di Trento) -
21
Teleparallel dark energy in a nonflat universe
We investigate the cosmological dynamics of teleparallel dark energy in the presence of nonzero spatial geometry. We specifically analyze nonminimal scalar-tensor theories in the torsion-based framework by considering different scalar field potentials and examining the resulting background evolution and linear perturbations. Adopting a dynamical systems approach, we reformulate the field equations and constrain the model parameters via a Markov chain Monte Carlo analysis combining updated datasets from Pantheon+SH0ES supernovae, cosmic chronometers, and growth rate measurements. Our results suggest a mild preference for an open geometry, although all models remain consistent with a flat universe at the $1\sigma$ level. Notably, Bayesian information criteria indicate that the nonflat teleparallel scenario with a vanishing potential is strongly favored over the standard $\Lambda$CDM model. Furthermore, all teleparallel scenarios are compatible with local determinations of the Hubble constant and exhibit better agreement with low-redshift structure formation data compared to $\Lambda$CDM. These findings highlight the potential of nonflat teleparallel gravity to address current observational tensions and motivate its further investigation as a viable alternative to standard cosmology.
Speaker: Prof. Rocco D'Agostino (Scuola Superiore Meridionale) -
21:00
Welcome Reception
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08:00
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22
Lost beyond ΛCDM
As cosmological observations reach unprecedented precision, the standard $\Lambda$CDM model is facing mounting pressure on multiple fronts. The well-known Hubble tension — a persistent $\sim 5 \sigma$ discrepancy between early- and late-universe determinations of the Hubble constant — challenges the foundations of our baseline paradigm. At the same time, recent Baryon Acoustic Oscillation measurements from DESI suggest bounds on the sum of neutrino masses that increasingly conflict with lower limits from particle physics, assuming standard cosmology. Extensions to the dark energy sector, particularly evolving dark energy models, can alleviate the neutrino mass tension and even appear to disfavor a cosmological constant at $\sim 3-4\sigma$. Yet these scenarios generally fail to address the Hubble tension. Conversely, both early- and late-time solutions proposed for the Hubble tension often drive the neutrino mass toward unrealistically small values, worsening the conflict with particle physics. This raises a natural question: is a coherent framework capable of reconciling all datasets still within reach, or is the cosmological blanket simply too short, such that pulling to cover one discrepancy inevitably leaves another exposed? In this talk, I will explore the web of tensions currently plaguing modern cosmology, and outline possible pathways into the beyond-$\Lambda$CDM swampland.
Speaker: Dr William Giarè (Sheffield U.) -
23
Cosmology and Tensions with Broken Spacetime Symmetries
TBA
Speaker: Prof. Nils A. Nilsson (Institute for Basic Science, Korea) -
24
The interacting dark energy model
We explore an interacting dark sector model in trace-free Einstein gravity where dark energy has a constant equation of state, w=-1, and the energy-momentum transfer potential is proportional to the cold dark matter density. Compared to the standard ÎCDM model, this scenario introduces a single additional dimensionless parameter, ε, which determines the amplitude of the transfer potential. Using a combination of Planck 2018 Cosmic Microwave Background (CMB), DESI 2024 Baryon Acoustic Oscillation (BAO), and Pantheon+ Type Ia supernovae (SNIa) data, we derive stringent constraints on the interaction, finding ε to be of the order of ~10^{-4}. While CMB and SNIa data alone do not favour the presence of such an interaction, the inclusion of DESI data introduces a mild 1Ï preference for an energy-momentum transfer from dark matter to dark energy. This preference is primarily driven by low-redshift DESI BAO measurements, which favour a slightly lower total matter density Omega_m compared to CMB constraints. Although the interaction remains weak and does not significantly alleviate the H0 and S8 tensions, our results highlight the potential role of dark sector interactions in late-time cosmology.
Speaker: Dr Yuejia Zhai (University of Sheffield) -
25
How neutrinos can help solving cosmological anomalies and tensions
I will discuss how (non-standard) neutrino properties can address some cosmological anomalies of different nature such as the neutrino mass tension, NANOGrav, potential Deuterium problem, excess radio background, non-standard 21cm cosmological global signal. At the same time they might also contribute to ameliorate the Hubble tension. I will discuss a few models able to connect and explain simultaneously some of these tensions/anomalies.
Speaker: Prof. Pasquale Di Bari (University of Southampton) -
11:10
Coffee Break
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26
Phantoms and early dark energy in axio-dilaton cosmology
I will introduce the axio-dilaton models of dark energy where the dilaton plays the role of quintessence and the axion induces a new way of screening long range forces. We will see that the screening properties of these models lead to early dark energy related to the axion potential and phantom crossing from the coupling of the dilaton to matter.
Speaker: Prof. Philippe Brax (IPhT Paris-Saclay) -
27
Cosmic choreographies Dark matter, gravitational waves and the Waltz of black holes
The Universe, as described by the standard model of Cosmology, is a vast ocean of darkness-dominated by dark matter and dark energy, with only a trace of luminous matter giving rise to the cosmic web we observe today. Yet this seemingly insubstantial fraction has shaped galaxies, clusters, and filaments across billions of years. What remains largely invisible, however, may hold the key to unlocking some of the Universe's deepest secrets. Dark matter, inferred from gravitational signatures like galaxy rotation curves, continues to elude direct detection. But a new frontier has opened up the realm of gravitational-wave physics. With detectors now regularly capturing the ripples in spacetime from black-hole binaries, a powerful bridge is emerging between Cosmology and Gravitational Waves. This talk explores how gravitational waves-long studied under the assumption of a vacuum spacetime-can be influenced by their astrophysical surroundings, particularly dark matter halos. I will present cutting-edge research on how these subtle environmental effects can leave fingerprints on gravitational-wave signals, offering a promising pathway to probe the nature and constrain dark matter models through a new observational channel.
Speaker: Dr Kyriakos Destounis (CENTRA, Instituto Superior Tecnico, Lisboa) -
28
Spectroscopic tests of cosmology and fundamental physics
Modern physical theories rest on two foundational assumptions general covariance, which holds that the laws of physics are valid across all of space-time, and the cosmological principle, which asserts that no observer occupies a special location in the universe. Both principles can be empirically tested through astronomical spectroscopy. Tests of general covariance involve searching for spatial or temporal variations in fundamental constants, such as the fine-structure constant (α). Meanwhile, the cosmological principle can be examined by measuring variations in total optical depth across different lines of sight in the universe. In this talk, I will review recent constraints from VLT/ESPRESSO on Îα/α and outline the potential of upcoming facilities, including the ELT-HIRES and the proposed Wide-field Spectroscopic Telescope, to provide tighter constraints and probe deeper into the structure and isotropy of the universe.
Speaker: Prof. Dinko Milakovic (Institute for Fundamental Physics of the Universe) -
29
Addressing the Hubble tension in Yukawa cosmology?
In Yukawa cosmology, a recent discovery revealed a relationship between baryonic matter and the dark sector. The relation is described by the parameter α and the long-range interaction parameter λ - an intrinsic property of the graviton. Applying the uncertainty relation to the graviton raises a compelling question: Is there a quantum mechanical limit to the measurement precision of the Hubble constant (H0)? We argue that the uncertainty relation for the graviton wavelength λ can be used to explain a running of H0 with redshift. We show that the uncertainty in time has an inverse correlation with the value of the Hubble constant. That means that the measurement of the Hubble constant is intrinsically linked to length scales (redshift) and is connected to the uncertainty in time. On cosmological scales, we found that the uncertainty in time is related to the look-back time quantity. For measurements with a high redshift value, there is more uncertainty in time, which leads to a smaller value for the Hubble constant. Conversely, there is less uncertainty in time for local measurements with a smaller redshift value, resulting in a higher value for the Hubble constant. Therefore, due to the uncertainty relation, the Hubble tension is believed to arise from fundamental limitations inherent in cosmological measurements. Finally, our findings indicate that the mass of the graviton fluctuates with specific scales, suggesting a possible mass-varying mechanism for the graviton.
Speaker: Prof. Genly Leon Torres (Catolica del Norte U.) -
30
Exploring Cosmic Evolution and Tensions in Teleparallel f(T) Gravity
Cosmology currently faces significant challenges due to persistent tensions between independent observational datasets. Resolving these discrepancies within a unified framework would strengthen confidence in any proposed cosmological model and may require going beyond General Relativity. One compelling alternative is Teleparallel Gravity, a torsion-based formulation of gravity that offers a different geometric interpretation of gravitation. In this study, we explore f(T) gravity, a class of models that has shown promise in describing cosmic evolution. We perform a detailed analysis of prominent f(T) models using a range of late-time cosmological datasets, including Pantheon+ (PN+), Cosmic Chronometers (CC), Baryon Acoustic Oscillations (BAO), and Redshift-Space Distortions (RSD). In addition, we extend our investigation to early-time physics by incorporating CMB B-mode polarization data from BK18, which is sensitive to primordial gravitational waves generated during inflation. This integrated approach enables a comprehensive exploration of key cosmological parameters and provides new insights into the nature of cosmological tensions within the framework of modified gravity.
Speaker: Dr Rebecca Briffa (Institute of Space Sciences and Astronomy, University of Malta) -
13:20
Lunch Break
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31
Holographic Spacetime Foam: Theory and Observations
Spacetime is foamy: it undergoes quantum fluctuations, with distance uncertainty scaling as the cube root of distances, consistent with the holographic principle - hence the name "holographic spacetime foam" (HSF) (also known as "holographic quantume foam"). HSF, in conjunction with thermodynamics, naturally demands the existence of a dark sector, the quanta of which obey infinite statistics. Applied to the cosmos, HQF yields a cosmology with critical energy density and a dynamical cosmological constant, as well as a phenomenologically viable dark matter sector. An early cosmic acceleration can also be traced to HQF. Most importantly, it is verified by observations of gamma-ray burst GRB 221009A: the brightest ever seen in the optical/near-infrared through to X-rays; even at 251 TeV. That is possible only for HSF if accounting for how real telescopes see foam.
Speakers: Eric Steinbring (NRC/HAA), Prof. Y. Jack Ng (University of North Carolina at Chapel Hill) -
32
Influence on S8 Discrepancy in Modified Gravity
Cosmological tensions have questioned the validity of the concordance model, opening avenues for new physics. One possible alternative is to model the cosmological expansion of the Universe using alternative gravitational models. In this talk, the scalar-tensor and teleparallel gravity paradigms are discussed within the context of large-scale structure formation and how the growth structure equations can be used to investigate the viability of such models using various observational data sets. The derived growth structure equations shall explore how it influences the growth index parameter, hence outlining the role of modified gravity theories on the s8 discrepancy. The talk will also discuss the behaviour of the subhorizon limit and how the chosen modified gravity model ansatzes influence the wavenumber when such limit is valid.
Speaker: Dr Gabriel Farrugia (University of Malta) -
33
Inflation in Scalar-Torsion Gravity From Single-Field Dynamics to Multi-Field Extensions
The inflationary paradigm remains the leading candidate for explaining the early universe's homogeneity, isotropy, and the origin of cosmic perturbations. However, its compatibility with current observational data and the persistent tensions within the ÎCDM model motivate the exploration of alternative gravitational frameworks. In this talk, we delve into the dynamics of cosmic inflation within the context of scalar-torsion gravity and its multi-field extensions, specifically within the realm of modified teleparallel gravity. This framework offers a compelling alternative to General Relativity, introducing new gravitational degrees of freedom and modified inflationary dynamics that can lead to distinct predictions for the primordial scalar and tensor power spectra, thereby offering new avenues to address current cosmological tensions.
Speaker: Prof. Giovanni Otalora (University of Tarapaca, Chile) -
34
Cosmic Microwave Background telescopes and the APPEC roadmap
One of the major challenges of modern cosmology is the detection of primordial Bâmode polarization anisotropies in the CMB, a smoking gun for inflation. The B-modes is the most promising direct observational signature of the inflationary phase that is thought to have taken place in the early Universe, generating primordial perturbations, producing Standard Model elementary particles and giving its generic features to our Universe (flatness, homogeneity. . .). Science aims at testing models of inflation by measuring or putting upper limits on r, the ratio of tensor fluctuations to scalar fluctuations. A detection of tensor modes would yield the first evidence of quantum gravity and point to inflationary physics near the energy scale associated with grand unified theories, probing energy scales far beyond the reach of the LHC or any conceivable collider experiment, and providing additional evidence in favour of the idea of the unification of forces. Results from Planck, BICEP and other previous and current experiments have shown how challenging is the search for primordial B-mode polarization because of many difficulties: weakness of the expected signal, instrumental systematics that could possibly induce polarization leakage from the large E signal into B, polarized foregrounds (dust) larger than anticipated⦠A review of results and projects will be given, including Simons Observatory, the Litebird satellite project, the goals of CMB-S4 which has been recently ended, QUBIC, with a technical demonstrator installed in Argentina and starting commissioning observations. Concerning the difficult disentangling primordial B-polarization from complex, decorrelated foregrounds, the contribution of the Pasiphae project, in Crete and Sutherland, will be outlined.
Cosmology is one of the research fields included in the scope of the Astroparticle Physics European Consortium, which is preparing the road map of the European astroparticle physics strategy 2027-2036. The preparatory document for the Town Meeting of September 23-24 in Zaragoza has been written after community surveys and will soon be available. The open questions and priority projects in CMB science to be recommended will be discussed.Speaker: Prof. Sotiris Loucatos (Irfu CEA Saclay and APC) -
35
Addressing the H0 and S8 tensions in f(Q) cosmologySpeaker: Dr Maria Petronikolou (National Observatory of Athens)
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17:20
Coffee Break
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36
Realising DM and NANOGrav data via Dark Branes
In this work we propose a setup for the origin of dark matter based on spacetime with a warped extra dimension and three branes: the Planck brane, the TeV brane and a dark brane, at a (sub)-GeV scale. The Standard Model is localized in the TeV brane, thus solving the Higgs hierarchy problem, while the dark matter χ, a Dirac fermion, is localized in the dark brane. The dark matter has only gravitational interactions with the Standard Model and we show that it can easily reproduce the thermal relic density by annihilations into radions and avoid direct detection experiments. The dark brane comes with a conformal sector confining at a 1st order phase transition generating a stochastic gravitational waves background which can accommodate the recent NANOGrav signal. A region in the parameter space of dark matter and radion masses is selected.
Speaker: Dr Fotis Koutroulis (IHEP, Beijing) -
37
Quantum Gravity Meets DESI Dynamical Dark Energy in Light of Swampland Trans-Planckian Censorship Conjecture
As an implication from Quantum Gravity, the swamplandish TransâPlanckian Censorship Conjecture (TCC) prohibits eternal cosmological acceleration, a prediction that aligns naturally with the quintom-B behavior from the latest DESI DR2 data. Primarily, we implement TCC bounds within the framework of dynamical dark energy, especially in the w0waCDM parametrization and f(T), f(Q) modified gravities, demonstrating that TCC is very powerful to constrain or exclude them. Our findings imply that viable dynamical dark energy scenarios must asymptotically transit to deceleration, shedding light on new physics consistent with both cosmological observations and fundamental Quantum Gravity principles.
Speaker: Prof. Junkai Wang (Tsinghua U.) -
38
From N to (N,p) Attractors in view of ACT
We develop a new class of inflationary attractors which
are compatible with the recent ACT results. They are based on
fractional Kaehler potentials, $K$, for a gauge-singlet inflaton
$\sg$ which reduce, along the inflationary path, to the form
$N/(1-\sg^{q})^{p}$ with $q=1, 2$ and $0.1\leq p\leq10$. The
combination of these $K$'s with the chaotic potentials $\phi^n$
(where $n=2, 4$) within a non-linear sigma model leads to
inflationary observables which are consistent with the current
data and largely independent from $q$ and $n$. Endowing these
$K$'s with a shift symmetry we also offer a supergravity
realization of our models introducing two chiral superfields and a
monomial superpotential, linear with respect to the
inflaton-accompanying field. Inflation is attained with
subplanckian inflaton values and yields large values for the
tensor-to-scalar ratio which increases with $N$.Speaker: Dr Constantinos Pallis (Aristotle University of Thessaloniki) -
39
Cosmological tension implications for a non-minimally coupled dark matter with dark energy
Recently, various cosmological tensions have arisen for the standard model of cosmology. For the Hubble-constant $H_0$ tension, we have proposed a series of no-go "theorems" for possible deviations from the $\Lambda$CDM model. For the Hubble-variation $\delta H_0$ tension, we have found novel evidence for going beyond the $\Lambda$CDM model in a non-trivial manner. For the intercept $a_B$ tension, we have developed a diagnostic for systematics of supernovae. For recent hint of dynamical dark energy, we have proposed a specific interacting dark matter-dark energy model to minic the phantom crossing as a mis-modeling artifact, and we also resolve the $\Omega_m$ tension among Planck-CMB, DESI-BAO, and DES-SNe for both $\Lambda$CDM and $w_0w_a$CDM models. The conclusion seems to prefer a special kind of interacting dark matter and dark energy model.
Speaker: Prof. Shao-Jiang Wang (IThP, Chinese Academy of Sciences) -
40
TDCOSMO 2025 Cosmological constraints from strong lensing time delays
Time-delay cosmography with lensed quasars is a one-step method for estimating the Hubble constant in the local Universe independently of the cosmic distance ladder. It does not require any intermediate calibration and relies on measuring the time delays between multiple images of strongly lensed quasars, which are inversely proportional to the Hubble constant. In this talk, we present cosmological constraints from eight strongly lensed quasars (hereafter, the TDCOSMO-2025 sample), based on a new blind analysis by the TDCOSMO collaboration designed to prevent experimenter bias. Building on previous work, we have improved our modeling of line-of-sight effects, the surface brightness profiles of lens galaxies, and stellar orbital anisotropy, and we have corrected for projection effects in the lens dynamics. Our uncertainties are maximally conservative, accounting for the mass-sheet degeneracy in the deflectorsâ mass density profiles, constrained by new measurements of stellar velocity dispersions from spectra obtained with the James Webb Space Telescope (JWST), the Keck Telescopes, and the Very Large Telescope (VLT), and using improved methods. Our primary result, H_0 = 72.1+4.0â3.7 km/s/Mpc, is derived from the TDCOSMO-2025 sample combined with Ω_m constraints from the Pantheon+ Type Ia supernova (SN) dataset. We also present measurements of the Hubble constant combining TDCOSMO-2025 with external datasets from the Sloan Lens ACS (SLACS) and Strong Lenses in the Legacy Survey (SL2S) lens sample, further improving the precision. The Hubble constant measurement is robust against the addition of external lens samples, the choice of different cosmological models beyond the ÎCDM model, and the use of the Ω_m prior from other datasets, such as the DESI DR2 BAO or the DES Year-5 SN sample.
Speaker: Dr Martin Millon (ETHZ) -
20:00
CONFERENCE DINNER (GREEK NIGHT)
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22
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41
Multi-survey cosmology from galaxy clustering and weak lensing
The inferred cosmological information is most robust when multiple probes are combined. Two of the most sensitive probes of the large-scale structure of the universe are galaxy clustering and weak lensing. I will present new cosmological results combining those two probes (in a so-called 3x2pt analysis) using DESI DR1 spectroscopic data for the galaxy clustering and weak lensing data from the DES, KiDS and HSC surveys.
Speaker: Anna Porredon (CIEMAT, Madrid) -
42
A f(R)esh look at the dynamics of modified gravitySpeaker: Prof. Peter Dunsby (University of Cape Town)
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43
The Palatini approach for cosmology and black hole physicsSpeaker: Prof. Diego Rubiera-Garcia (Complutense University of Madrid)
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44
A New Master Supernovae Ia sample and the investigation of the H_0 tension
Modern cosmological research still thoroughly debates the discrepancy between local probes and the Cosmic Microwave Background observations in the Hubble constant (\texorpdfstring{$H_0$}{H0}) measurements, ranging from 4 to 6$Ï$. In the current study, we examine this tension using the Supernovae Ia (SNe Ia) data from the Pantheon, Pantheon+ (P+), Joint Lightcurve Analysis (JLA), and Dark Energy Survey, (DES) catalogs combined together into the so-called Master Sample. The sample contains 3714 SNe Ia, and is divided all of them into redshift-ordered bins. Three binning techniques are presented the equi-population, the moving window (MW), and the equi-spacing in the \texorpdfstring{$\log-z$}{log-z}. We perform a Markov-Chain Monte Carlo analysis (MCMC) for each bin to determine the $H_0$ value, estimating it within the standard flat \texorpdfstring{$Î$CDM}{LCDM} and the \texorpdfstring{$w_{0}w_{a}$CDM}{w0waCDM} models. These \texorpdfstring{$H_0$}{H0} values are then fitted with the following phenomenological function \texorpdfstring{$\mathcal{H}_0(z) = \tilde{H}_0 / (1 + z)^α$}{H0(z) = H0tilde / (1 + z)^alpha}, where \texorpdfstring{$\tilde{H}_0$}{H0tilde} is a free parameter representing \texorpdfstring{$\mathcal{H}_0(z)$}{H0(z)} fitted in \texorpdfstring{$z=0$}{z=0}, and \texorpdfstring{$α$}{alpha} is the evolutionary parameter. Our results indicate a decreasing trend characterized by \texorpdfstring{$α\sim 0.01$}{alpha ~ 0.01}, whose consistency with zero ranges from $1 Ï$ in 5 cases to 1 case at 3 $Ï$ and 11 cases at $> 3 Ï$ in several samples and configurations. Such a trend in the SNe Ia catalogs could be due to evolution with redshift for the astrophysical variables or unveiled selection biases. Alternatively, intrinsic physics, possibly the \texorpdfstring{$f(R)$}{f(R)} theory of gravity, could be responsible for this trend.
Speaker: Prof. Maria Giovanna Dainotti (NAOJ) -
11:10
Coffee Break
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45
Cosmological Tensions and the Viability of f(Q) GravitySpeaker: Prof. Amare Abebe (Centre for Space Research, North-West University)
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46
Cosmology with Rubin Observatory's Legacy Survey of Space and Time
The Vera Rubin Observatories Legacy Survey of Space and Time will open an unprecedented view of our universe with the survey slated to begin this fall. I will review status and results from the Observatory thus far as well as the major cosmological probes for LSST and expectations for the constraints to come.
Speaker: Prof. Tesla Jeltema (UC, Santa Cruz) - 47
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48
The challenges of using Baryon Acoustic Oscillations distances for cosmology
Baryon Acoustic Oscillations are considered one of the most powerful cosmological probes. They are generally deemed to provide distance measures independent of a specific cosmological model. At the same time the obtained distances are considered agnostic with respect to other cosmological observations. However, in current measurements, the inference is done assuming parameter values of a fiducial flat-LCDM model and employing prescriptions tested to be unbiased only within some flat-LCDM-like fiducial cosmologies. Moreover the procedure needs to face the ambiguity of choosing a specific correlation function model-template to measure cosmological distances. Does this comply with the requirement of model and parameter independent distances useful, for instance, to select cosmological models, detect Dark Energy and characterize cosmological tensions? In this talk I will review the subject, answer compelling questions and explore new promising research directions.
Speaker: Prof. Stefano Anselmi (INFN-Padova) -
49
The stochastic gradient flow approach to out-of-equilibrium complex systems in particle and gravitational physics, and its phenomenological implications
We have proposed a novel approach to investigate, in a geometrical way, the renormalization group equations for particle physics and gravity. The Stochastic gauge geometry flow hence introduced entails the breakdown of symmetries in the infrared, where the classical theory is recovered. We show several phenomenological implications for cosmology and astrophysics, QCD confinement and the measurement problem. Finally, we propose a scenario according to which the ultraviolet completion of General Relativity is realized through a stochastic gradient flow towards a topological BF theory, considering the flow of a pre-geometric theory proposed by Wilczek.
Speaker: Prof. Antonino Marciano (Fudan University & INFN) -
13:20
Lunch Break
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50
The role of massive elliptical galaxies on the CMB
Elliptical galaxies formed very rapidly, with the more massive ones forming faster, on a timescale shorter than a Gyr. The high metallicities of these galaxies imply them to have had significantly top-heavy galaxy-wide stellar initial mass functions. In other words, the synthesis of the heavy elements on such a short time scale in these galaxies implies them to have been 10000 times brighter than today. Given the region of space needed to have formed a single galaxy and their present-day separations, their formation occurred at a redshift near 17, in agreement with current JWST observations. Since star formation produces dust, the thermalised dust radiation from these galaxies is calculated to have been at least 1.4 per cent, and probably all, of the observed CMB photon energy. The implications of this finding, which merely rests on well observed properties and well understood physical laws, for contemporary cosmological theory is catastrophic, implying the need of an entirely novel cosmology to be developed. This work has been done in collaboration with Eda Gjergo from Nanjing University.
Speaker: Prof. Pavel Kroupa (Charles University/Bonn University) -
51
Gaussian Process Data Reconstruction and Modified Gravity Realization of Dynamical Dark Energy
Along with the accumulated cosmological observations, the standard paradigm of modern cosmology has been verified with high precision. Some new challenges such as the $H_0$ tension also appear. To address these issues, we reconstruct the cosmological evolution in a model-independent manner with the help of Gaussian process using the combined observational data. We extract the reconstructed dark-energy equation-of-state parameter, showing that it exhibits dynamic evolution. We investigate under what situation this type of evolution could be achieved from the perspectives of modified gravity. In particular, we reconstruct the corresponding actions for f(T) modified gravity. Since the reconstruction procedure is completely model-independent, the obtained data-driven reconstructed f(T) form could release the tensions between ÎCDM estimations and local measurements.
Speaker: Dr Xin Ren (USTC, China) -
52
Probing Tensions in the LCDM Paradigm Through Kinematics and Lensing in Galaxy Clusters
Galaxy clusters are excellent natural laboratories to study the nature of gravity and highlight possible tensions with the LambdaCDM scenario, at the edge between cosmology and astrophysics. Cluster mass profiles, determined through different methods, provide critical information on the distribution and interplay of baryonic matter, dark sector, and gravity. I present recent results obtained by using the updated version of MG-MAMPOSSt, a code that reconstructs the mass distribution of galaxy clusters or groups with kinematics and lensing analyses in GR and in viable modified gravity/Dark Energy frameworks. By means of high quality imaging and spectroscopic data, I will show the constraints that can be placed on the parameter space of viable alternatives to LambdaCDM, as well as on the shape of the Dark Matter distribution down to the very central regions of clusters. I will further focus on the strength and limitations of the method as well as future exciting lines of investigation that may explore new directions and narrow the allowed space of alternatives to the "Concordance" model.
Speaker: Prof. Lorenzo Pizzuti (University of Milano-Bicocca) -
53
GW, PTA, CMB and Neff Bounds
We investigate whether an Early-Universe stochastic gravitational–wave back-
ground (SGWB) can account for the common-spectrum process reported by
NANOGrav, while also being consistent with current and projected CMB measure-
ments of extra radiation. We compute the contribution of effective number of rela-
tivistic species, ∆Neff, for a number of Early-Universe models proposed to explain
the pulsar timing array (PTA) spectrum. We demonstrate that models predicting
∆Neff above the CMB limit would be firmly excluded, implying that the NANOGrav
signal in tension with these bounds must instead arise from astrophysical sources.
We find that current NANOGrav 15-year dataset, sensitive up to 60 nHz, gives a
negligible contribution to ∆Neff and remains well below the present and future
CMB detection threshold. However, when we project future PTA capabilities reach-
ing upto 1 µHz, even with our conservative estimate we find that Inflation, Scalar
Induced Gravitational Waves (SIGW), and metastable cosmic strings can induce a
∆Neff large enough for >3.5σ detection by the Simons Observatory.Speaker: Prof. Ido Ben-Dayan -
54
The 33311 Left-Right Bilepton Model (SM) A Model of Dark Matter and Energy (CO)Speaker: Prof. Paul Frampton (U of Salento)
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17:20
Coffee Break
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55
The local void solution to the Hubble tension
Cosmology is currently in a crisis known as the Hubble tension, the observation that redshift increases with distance about 10% faster than expected in the ÎCDM standard cosmological paradigm with parameters calibrated to fit the CMB anisotropies. A promising explanation for this is that we live near the centre of a large local underdensity or void. This is suggested by observations of source number counts across the whole electromagnetic spectrum, with near-infrared results implying that the density is about 20% below average out to 300 Mpc across 90% of the sky and most of the galaxy luminosity function (ApJ, 775, 62). Outflows from this KBC void can induce enough extra redshift to plausibly solve the Hubble tension (MNRAS, 499, 2845). I will discuss various tests of this proposal. At low redshift, the bulk flow of galaxies traces the average velocity of matter within a sphere centred on our location. The observed bulk flow curve is in good agreement with the void model predictions (MNRAS, 527, 4388). Looking further out, it is possible to infer the H0 parameter from data in a narrow redshift range centred on z. Such an empirical H0(z) curve agrees quite well with expectations in the void model, which predicts a return to the CMB-derived H0 beyond the void (MNRAS, 536, 3232). This result is related to recently submitted work on baryon acoustic oscillations (BAOs), which show a deviation from ÎCDM expectations (Arxiv 2501.17934). I will explain how the BAO observables would be affected by a local void. I will then present BAO results compiled over the last twenty years. These results fit better if the local void is included, thanks to good agreement with ÎCDM at high redshift but a persistent anomaly at lower redshift.
Speaker: Dr Indranil Banik (ICG Portsmouth) -
56
Self-Interacting Scalar Field Dark Matter Core-Halo relation
Scalar field dark matter (SFDM) is an alternative candidate to standard dark matter models, gaining attention due to the unique effects associated with its ultra-light mass. While its dynamics have been extensively studied across different scales, its full phenomenology remains under active investigation. In particular, the role of self-interactions and their impact on structure formation are still open questions. In this talk, I will explore the effects of both attractive and repulsive self-interactions in SFDM, with a focus on the evolution of the mass fraction and the core-halo relation. I will discuss analytical models proposed in the literature to describe dark matter halo cores and compare them with results from three-dimensional simulations. These findings will provide a basis for establishing comparisons between theoretical predictions and observational data, allowing us to impose constraints on the self-interaction term.
Speaker: Prof. Jessica Nayely Lopez Sanchez (Central European Institute for Cosmology and Fundamental Physics) -
57
New tools for cosmology by Extended Theories of Electro-Magnetism
We face the dichotomy of an ad hoc dark Universe compatible with GR but lacking experimental confirmation and unsupported by the SM, while we witness the continuous successes of GR. The latter do not impede a multitude of rightly efforts in reformulating gravitation, also for facing suspected or known limitations in the regime of strong field and of quantum scale. Among the messengers of the cosmos, despite the detection of neutrinos, cosmic rays and lately gravitational waves, photons remain by large the main carriers of information. But we stick reading such signals with the XIX Maxwellian theory, although it lacks explaining phenomena as photon interaction, splitting, merging. Conversely, we analyse signals to assess whether Extended Theories of Electro-Magnetism (ETEM) induce a (partial) reinterpretation of the laws in physics, bearing an impact on cosmology. The SM Extension (SME) dresses the photon with an effective mass [1,2], the only free massless particle remained in the SM. Such a mass is compatible with the upper limits obtained through Fast Radio Bursts [3-5] and solar wind [6,7], that this collaboration was recognised for by the Particle Data Group. Birefringence, group velocity dispersion, second-order QED are tested or searched ETEM effects in running experiments, e.g., BMV Toulouse, ATLAS CERN, DeLLlight Paris. But other phenomenology can be addressed too. Indeed, all photons either massive - ab initio as in the de Broglie-Proca theory or with an effective mass from the SME or from the Born-Infeld, Heisenberg-Euler non-linear type of theories - undergo a frequency shift in presence of an electromagnetic and/or a Lorentz Symmetry Violation background [8,9]. This shift, even when small, added to the expansion redshift, determines new cosmological scenarios, e.g., without accelerated expansion [10-12] and possibly without dark matter [work in progress]. Based on earlier work [13-15], we are now turning to study the self-force on a photon, for which the frequency shift would occur due to the interaction of the photon energy with the curvature produced by an electromagnetic field. Testing this shift through (atom) interferometry is of pivotal importance [16,17]. The upper limit lies at 3 x 10-18 in Îν/ν for an optical length equal to the Earth-Moon distance. On the bottom line, we recall that expansion is just an interpretation of observations, like the dark universe, and not falsifiable at laboratory scale since it occurs only at large scale. Thereby a frequency shift would imply a small scale expansion or an ETEM confirmation. Finally, we implement the Heisenberg principle at cosmological distances. The minimal mass is drawn from the energy-time relation for time equal to the age of the universe. The Hubble tension [18] would be a quantum measurement interpreted as intrinsic limit of the observations [19,20].
Speaker: Prof. Alessandro Spallicci (Orleans U) -
58
GalSBI: Forward modelling galaxy surveys with simulation-based inference
Stage IV galaxy surveys will test the cosmological model with unprecedented precision, providing critical insights into tensions like the S8 discrepancy and probing evolving dark energy scenarios. To fully realize the potential of these surveys, forward modeling of galaxy populations offers a promising pathâenabling both accurate redshift calibration and a deeper understanding of galaxy properties. In this talk, I will present GalSBI and SHAM-OT, two complementary frameworks that together enable the construction of highly realistic galaxy distributions in cosmological simulations. GalSBI is a phenomenological galaxy population model based on parametric descriptions of luminosity functions, morphologies, and spectral energy distributions. It is constrained through simulation-based inference, comparing Hyper Suprime-Cam imaging data to forward-modeled image simulations that incorporate all relevant observational, instrumental, and source extraction effects. GalSBI reproduces observed galaxy magnitudes, colors, sizes, and redshift distributions with high fidelity, and is available as an open-source Python package. To complement GalSBI's photometric realism with accurate spatial distributions, we developed the SHAM-OT framework, which reformulates subhalo abundance matching as an optimal transport problem. This enables the efficient assignment of galaxies to dark matter halos, achieving orders-of-magnitude improvement in computational efficiency over traditional methods. Together, GalSBI and SHAM-OT are a powerful framework for creating synthetic catalogs that accurately capture both the photometric and spatial properties of observed galaxy populations, offering a crucial tool for current and next-generation cosmological surveys.
Speaker: Prof. Silvan Fischbacher (ETH Zurich) -
59
A Natural Expansion of the Cosmological Vacuum
We are in a golden era of cosmology, driven by increasingly precise observations and deep surveys of large-scale structure. While the ÎCDM modelâwith Einsteinâs cosmological constant Î and cold dark matterâremains successful, persistent tensions like the Hubble constant discrepancy suggest it may be incomplete. This talk explores whether general relativity is truly general. We argue that its flat Minkowski vacuum is not equivalent to the conformally scaled cosmological vacuum. By allowing gravity to couple to the trace J of the Schouten tensor, we introduce a Machian sensitivity to background curvature. This leads to a new analytic model for cosmic expansionâJCDMâthat shares the ÎCDM parameter space but differs in vacuum structure (5/6 classical, 1/6 non-classical). JCDM agrees with key observations, including the Planck CMB, local Hubble measurements, and DESIâs baryon acoustic oscillation data. Notably, it predicts a Hubble constant higher by a factor of \sqrt{6/5} compared to ÎCDM, offering a natural resolution to the current Hubble tension. (Ref. van Putten, 2025, JHEAP, 45, 19)
Speaker: Prof. Maurice van Putten (Sejong University/INAF-OAS) -
60
Galaxy-galaxy lensing application on cosmology
Gravitational lensing is one of the indirect methods for detecting dark matter, allowing us to reconstruct the mass distribution of foreground objects and provide insights into their gravitational fields and dynamics, which can be used to study the properties of dark matter halos and test gravitational theories. Galaxy-galaxy lensing provides an effective approach to studying the distribution of dark matter at the galactic scale and testing cosmological models. Which can be used to study the mass-concentration relation of dark matter halos and, in conjunction with modified gravitational theories beyond general relativity, conduct observational tests of cosmological models.
Speaker: Dr Qingqing Wang (USTC, China)
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41
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61
Expanding the TRGB & JAGB SNe Ia Calibration Samples to Investigate Distance Ladder Systematics
Distance ladders which calibrate the luminosity of Type Ia supernovae (SNe Ia) currently provide the strongest constraints on the local value of H0. Recent studies from the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) show good consistency between measurements of SNe Ia host distances. These are calibrated to NGC 4258 using different primary distance indicators (Cepheids, Tip of the Red Giant Branch (TRGB), J-region Asymptotic Giant Branch (JAGB), and Miras). However, some sub-samples of calibrated SNe Ia employed to measure H0 yield noteworthy differences due to small sample statistics but also due to differences in sample selection. This issue is particularly important for TRGB-derived calibrations owing to the smaller volume they reach compared to Cepheids, reducing sample size and enhancing the size of statistical fluctuations. To mitigate this issue, we compile the largest and complete (as currently available) samples of TRGB and JAGB in the hosts of normal SNe Ia. The full TRGB sample together with the Pantheon+ SN catalog gives H0=72.1-73.3 +/- 1.8 km/s/Mpc (depending on methodology), while the JAGB sample yields H0 = 73.3 ± 1.4 (stat) ± 2.0 (sys) km/s/Mpc, both in good agreement with the value of 72.5 +/- 1.5 km/s/Mpc from HST Cepheids in hosts of 42 SNe Ia calibrated by the same anchor, NGC 4258. We also extend the JAGB distance scale to ~40 Mpc using NGC 5468 and characterize variations in the J-region luminosity function.
Speaker: Prof. Siyang Li (Berkeley U.) -
62
Cosmological implications of an Axion-Like Majoron
Recent observations in Physical Cosmology have achieved a precision that not only allows for a better determination of model parameters, but also, the existence of cosmological tensions between current datasets motivates exploiting this precision to test for alternative theories that extend the particle content of the Standard Model. Theories beyond the Standard Model of particle physics generally predict the existence of scalar fields whose excitations manifest as axion-like particles (ALPs). One such field is the majoron, which is an eV-scale neutrinophilic pseudo-Goldstone boson that is created in the oscillations of photons to axions in the presence of a primordial magnetic field. As the Universe cools down to a temperature below the majoron mass, they decay transferring their energy to the neutrino sector. This axion-like majoron has three interesting consequences for Physical Cosmology 1) This missing energy in the conversion of photons to axions is not accounted for in the standard LambdaCDM model, so the inferred cosmic expansion rate of the universe from Cosmic Microwave Background (CMB) measurements would be increased, potentially solving the Hubble tension (H0). 2) The baryon-to-photon ratio would also be decreased before the time of photon-to-axion oscillation, increasing the abundance of primordial deuterium formed at Big Bang Nucleosynthesis (BBN) and better matching primordial deuterium observations. 3) The extra contribution to the Cosmic Neutrino Background causes a small-scale suppression on structure formation due to free-streaming of massive neutrinos, contributing to the S8 tension, and enabling a possible degeneracy with the controversial interpretation of the cosmological neutrino mass signal from Large Scale Structure observations (LSS). Overall, the phenomenology of an axion-like majoron appearing at the end of BBN and decaying before recombination has the power to modify the interpretation of the observations of the major pillars of the Big Bang Theory, and is therefore a promising particle physics scenario with the potential for addressing the current Tensions in Cosmology.
Speaker: Prof. Antonio Cuesta (Cordoba U.) -
63
Biased domain walls: faster annihilation, weaker gravitational waves
We study the evolution of domain wall networks and their phenomenological implications in a model of a real scalar, where a Z2-symmetry is slightly broken by a potential bias. It is demonstrated that the latter triggers domain wall annihilation considerably earlier than previously thought. As a result, the energy density of gravitational waves produced by the network of biased domain walls, for a given tiny bias, is suppressed compared to naive expectations. The spectral shape of gravitational waves is similar to that resulting from unbiased domain walls, but with more power in the close-to-maximum ultraviolet part. In the far ultraviolet region, the spectrum of gravitational waves becomes nearly flat, such a plateau has been recognised earlier in the case of unbiased walls.
Speaker: Prof. Eugeny Babichev (IJCLab, Orsay) -
64
Thermodynamic Insights into Cosmic Acceleration Entropic Dark Energy and Observational Tensions
The late-time accelerated expansion of the universe remains a profound mystery, traditionally attributed to a cosmological constant or dark energy component. However, mounting observational tensions like Hubble tension have challenged the adequacy of the standard ÎCDM model and motivated alternative approaches. This study explores entropic dark energy models, which emerge from the thermodynamic interpretation of gravity and the holographic principle, offering a novel framework for cosmic acceleration rooted in fundamental physics. By incorporating generalized entropy-area relations and horizon thermodynamics, modified Friedmann equations are formulate which naturally give rise to an effective dark energy component. The cosmological dynamics of these entropic models are studied, focusing on their implications for the Hubble tension and other late-time anomalies such as the growth rate discrepancy. The results show that entropic dark energy models can mimic standard cosmology at early times while allowing for dynamical deviations at low redshifts, potentially easing existing tensions and thus provide deeper insights into the nature of dark energy and the underlying laws governing cosmic evolution.
Speaker: Prof. Sudipta Das (Visva-Bharati, Santiniketan, India) -
11:10
Coffee Break
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65
Construction of LambdasCDM model from compact internal space manifold
In this talk, we present a higher-dimensional framework in which the curvature of compact internal space can drive an effective sign change in the 4D cosmological constant, mimicking the behavior required by phenomenological extensions of ÎCDM. A spontaneous transition in the size of the extra dimensions leads to a mirror AdS-dS shift in the external spacetime, offering a novel geometric origin for late-time acceleration. This mechanism also predicts an evolving gravitational coupling and may offer new insight into existing cosmological tensions. Model-independent implications for the dynamics and observables will be discussed at the end of the talk.
Speaker: Prof. Nihan Katirci (Doğuş U.) -
66
Hubble H0 tension in nonlocal de Sitter gravity
Hubble H0 tension in nonlocal de Sitter gravity Branko Dragovich Institute of Physics, University of Belgrade, Belgrade, and Mathematical Institute of the Serbian Academy of Sciences and Arts, Belgrade, Serbia Email dragovich@ipb.ac.rs Abstract Despite its great success, the general theory of relativity is not the final theory of gravity. In addition to other problems, some shortcomings of the standard model of cosmology led to the search for a more general theory of gravity. One of the promising lines of research is the nonlocal theory of gravity. I will present a simple nonlocal de Sitter gravity model, its several exact vacuum cosmological solutions. One of cosmological solutions mimics effects that are usually assigned to dark matter and dark energy. Some other cosmological solutions are examples of the bounce and cyclic universes. In this talk, I will mainly consider one of the current problems of cosmology, which is related to cosmological tensions. In particular, I will present possible solution of H0 tension in our model of nonlocal de Sitter gravity, which supports H0 = 67.40 km/s/Mpc. Based mainly on joint work with I. Dimitrijevic, Z. Rakic and J. Stankovic 1. PLB 797 (2019) 134848, arXiv 1906.07560 [gr-qc]. \ 2. JHEP 12 (2022) 054, arXiv 2206.13515 [gr-qc] . 3. Symmetry 16 (2024) 544, arXiv 2404.05848 [physics.gen-ph].
Speaker: Prof. Branko Dragovich (Mathematical Institute, Serbian Academy of Sciences, Kneza Mihaila 36, Belgrade, Serbia) -
67
Dynamical heating in spin-s ULDM halos
Ultralight Dark Matter (ULDM) has emerged as a compelling alternative to the Cold Dark Matter paradigm at small scales, naturally producing solitonic cores at the center of halos and granular structures arising from wave interference. These features lead to distinctive dynamical effects, including the random motion of the core and dynamical heating of stars in galactic systems. In this work we explore dynamical heating in the context of spin-s ULDM models, which predict broader solitonic cores and modified transition radii compared to the scalar case. We discuss how interference, subhalo encounters, and wavelets inject kinetic energy into stellar populations, driving observable signatures such as size–age relations in dwarf galaxies and thickening of galactic discs. At large scales, spin-s ULDM converges to the standard ΛCDM behavior, preserving cosmological consistency while offering testable predictions at galactic scales. Our results highlight the importance of stellar dynamics as a probe of the ULDM framework and its higher-spin generalizations.
Speaker: Prof. Erick Munive Villa (CEICO-FZU) -
68
Inflation or quantum gravity?
We present two fundamental theories for the early Universe: (i) the first consists in an ultraviolet completion of the inflationary paradigm, (ii) the second instead replaces inflation with quantum gravity.
The thereatical framework is for both the scenarios a nonlocal unification of gravity and matter consistent with unitarity and finiteness at quantum level.In (i) the theory is designed in order to reproduce exactly the same results of a general $f(R)$ theory: in particular the Starobinsky model. This construction strongly support why we do not need quantum gravity to explain the cosmological data.
In (ii) the issue of standard cosmology find a natural solution in the Weyl conformal phase of the primordial Universe. The scale invariant CMB spectrum is due to the phase of quadratic gravity, while the logarithmic quantum corrections to the action make both the primordial tensor spectrum and the scalar spectrum quasi scale invariant. We predict a tensor index $n_t = 1 − n_s$, and a lower bound for tensor-to-scalar ratio $r_{0.05} > 0.009$.
Speaker: Prof. Leonardo Modesto (University of Cagliari) -
69
Kinetically coupled dark matter condensates and early formation of supermassive black holes
Dark matter consisting of ultralight bosons can form a macroscopic Bose-Einstein condensate with distinctive observational signatures. I will discuss a two-field generalization where an axion couples to a moduli field through its kinetic term, representing the phase and radial modes of a complex scalar field. This kinetic coupling produces dramatic modifications to cosmological evolution, and has implications in the formation of supermassive black holes by altering the Jeans scale, modifying energy transfer, and generating instabilities in soliton cores. Time permitting I will discuss how the solution to the H0 and S8 problems necessitate an early and late universe modification to LCDM.
Speaker: Prof. Savvas Koushiappas (Brown University) -
13:20
Lunch Break
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16:00
BOAT EXCURSION
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61
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70
Cosmology with large scale structures: from KiDS to DESC
Probes of the large scale structures can give us the much needed insight into the nature of the dark Universe. In this talk I will show the latest results from the Kilo Degree Survey (KiDS) and our prospect with the stage four survey LSST. I will focus on the 3x2pt analysis that combines weak gravitational lensing, galaxy-galaxy lensing and galaxy clustering, from its models to analysis.
Speaker: Prof. Marika Asgari (Newcastle U.) -
71
Angular redshift fluctuations as a new, complementary cosmological probe
In this talk I will introduce angular redshift fluctuations (ARF), a novel cosmological observable that, contrary to other standard probes that measure the counts and the shapes of galaxies, looks at the galaxies' redshifts and their fluctuations when projected under any given redshift shell. I will show ARF are found to be extremely sensitive to radial peculiar velocities, and also to the underlying density field. This means they are sensitive to the baryonic acoustic oscillations (BAO), and together with standard 2D angular clustering, ARF provide a unique window to the BAO in angle and redshift space. ARF have been applied to BOSS spectroscopic, measuring the growth rate and setting very strong constrains on deviations from general relativity. They have also been applied on photometric galaxy surveys like QUAIA, unveiling ARF's great complementary power ni searches for the non-Gaussianity parameter f_NL. I will conclude by discussing ARF's potential to provide alternative measurements of key cosmological and fundamental parameters when combined with 2D clustering and CMB lensing.
Speaker: Prof. Carlos Hernandez-Monteagudo (IAC, Tenerife) -
72
Dark Dimension Cosmology
I will discuss the swampland distance conjecture and the Dark Dimension proposal for the cosmological constant. I will then argue on the possibility that the dark dimension obtains large size by higher dimensional inflation, relating the weakness of the actual gravitational force to the size of the observable universe. I will show that the power spectrum of primordial density fluctuations from 5-dimensional inflation is consistent with present observations with deviations that can be tested in future observations, together with the shape of the bispectrum which differs from standard 4-dimensional single field inflation.
Speaker: Prof. Ignatios Antoniadis (LPTHE, Paris) -
73
Observations, biases and tensions
Observational biases are unavoidably present in cosmological data data, and very often very difficult to asses. At the same time, we are entering the era of "big data" cosmological surveys, where data analysis has to be automatized to a large degree. While these big data will provide opportunities for unprecedentedly precise statistical measurements, task of disentangling observational biases, effects of cosmological evolution of observed sources and genuine cosmological tensions will become even more challenging. In my talk, I will present selected recent results from our group illustrating nontrivial dependencies between galaxy evolution, their properties and large scale structure, and discuss consequences for cosmological measurements from new large surveys. (To be updated later)
Speaker: Prof. Agnieszka Pollo (National Centre for Nuclear Research and Jagiellonian University) -
11:10
Coffee Break
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74
Resilience and implications of adiabatic CMB cooling
I will talk about our work where we investigate deviations from the standard adiabatic evolution of the CMB temperature, $T_{\rm CMB}(z)$, using the latest Sunyaev-Zelâdovich effect measurements and molecular line excitation data. We reconstruct the redshift evolution of $T_{\rm CMB}(z)$ in a model-independent way using Gaussian Process regression as well by chi-sq statistics. By combining both datasets, we find good consistency with the standard evolution across the full redshift range, inferring a present-day CMB temperature compatible with ARCADE and FIRAS. Next, we test deviations from the standard scaling by adopting the parameterisation $T_{\rm CMB}(z) = T_0(1+z)^{1-\beta}$, where $\beta$ quantifies departures from adiabaticity. We discuss the implications of our findings, placing tight constraints on alternative scenarios of interest for cosmological tensions and fundamental physics.
Speaker: Prof. Ruchika Ruchika (INFN, Rome) -
75
Primordial black holes from non-Gaussian tails
Primordial black holes (PBHs), formed from the collapse of primordial fluctuations during the radiation-dominated era, provide a unique probe of small-scale primordial perturbations. The statistical properties of these fluctuations are crucial for determining the PBH abundance and spatial distribution. We show that even in relatively simple single-field inflation models, deviations from slow-roll can lead to significant non-Gaussian effects. Using the $\delta N$ formalism, we identify a class of models that generate non-Gaussian tails, for which the usual Taylor expansion of non-Gaussianity parameters fails to capture the full behavior. I will focus on the origin of such non-Gaussian tails in single-field models and discuss their implications for PBH abundance.
Speaker: Xiao-Han Ma (USTC China & IPMU) -
76
Interacting dark sector from entropy couplings
Interactions between dark matter and dark energy have been explored in a variety of contexts, with recent motivations coming from the ongoing cosmological tensions. However, many nonminimally coupled models are either strongly constrained by background observations or are phenomenological in nature. In this talk, I will present a new class of interacting Lagrangian models where scalar fields couple to the intrinsic entropy of matter. These couplings share similarities with the âpure-momentum transferâ models, modifying only the Euler equation at linear order. The new degrees of freedom associated with intrinsic entropy perturbations play a crucial role in suppressing or enhancing the matter power spectrum on small scales, while leaving key features of the CMB unchanged. Alongside their observational signatures, I will discuss the physical interpretation of these models in terms of non-equilibrium thermodynamics and the relation to non-adiabatic fluid models.
Speaker: Dr Erik Jensko (University College London) -
77
Decaying dark matter and direct collapse black holes
The origin of the high-redshift supermassive black holes (SMBHs) seen by JWST is an open puzzle in cosmology. We examine the possibility that decaying dark matter can provide the conditions necessary for the formation of these black holes. Decaying dark matter models that inject 1--13.6~eV radiation into the early universe can prevent the formation of Pop III stars by suppressing the molecular hydrogen abundance in pre-star-forming halos, which can lead to the conditions ripe for such SMBH formation. We show that accounting for (i) dark matter decay in the intergalactic medium and (ii) the flux of this radiation over the history of the halo, molecular hydrogen can be suppressed enough to lead to atomic cooling halos. These, in turn, may lead to direct collapse and could produce supermassive black holes of the type now being observed by JWST.
Speaker: Prof. James Dent (Sam Houston State University) -
13:00
Lunch Break
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78
Hubble (non-)tension. Historical analysis on the underestimation of error bars
An analysis of a historical compilation of Hubble-Lemaaitre constant values in the last 50 years gives a chi^2 value of the dispersion with respect to the weighted average much larger than the number of points, which has an associated probability that is very low. This means that Hubble tensions were always present in the literature, due either to the underestimation of statistical error bars associated with the observed parameter measurements, or to the fact that systematic errors were not properly taken into account in many of the measurements.
The fact that the underestimation of error bars for H_0 is so common might explain the apparent 4.4-sigma discrepancy by Riess et al. As a matter of fact, more recent precise H_0 measurements with JWST data by Freedman et al. using standard candles in galaxies find there is no tension with CMBR data, possibly indicating that previously Riess et al. had underestimated their errors. Here we have carried out a recalibration of the probabilities and we find that a tension of 4.4-sigma, estimated between the local Cepheid-supernova distance ladder and cosmic microwave background (CMB) data, is indeed a 2.1-sigma tension in equivalent terms of a normal distribution, with an associated probability 0.036 (1 in 28). This can be increased to an equivalent tension of 2.5-sigma in the worst cases of claimed 6-sigma tension.
Why is there so much noise and commotion surrounding Hubble tension after 2019? It is suggested here that this obeys a sociological phenomenon of "groupthink".
Speaker: Prof. Martin Lopez-Corredoira (Inst Astrofı́sica de Canarias) -
79
Living in a Machian world
I will explain the conceptual ideas of correlation geometry underlying the theory of Causal Fermion Systems. I will explain how correlation geometry is a good candidate for a fundamental mathematical structure as it is background independent by design. This realizes Mach's dream of a purely relational description of nature.
Speaker: Dr Claudio Paganini (Regensburg U./ TU Chemnitz) -
80
Illustrating the consequences of a misuse of σ8 in cosmology
The parameter σ8 is commonly used to quantify the amplitude of matter fluctuations at linear cosmological scales. However, its intrinsic dependence on h can introduce biases and couples the growth and Hubble tensions in an intricate way, when comparing the predictions of different models and/or datasets. For example, the bias found in models with large values of H0 is more prominent, artificially complicating the search for a model that can resolve the Hubble tension without exacerbating the growth tension. To address these challenges, an alternative parameter has been proposed: σ12. In this scenario, the worsening of the growth tension in different cases is much less pronounced than previously thought or may even be nonexistent.
Speaker: Prof. Matteo Forconi (La Sapienza, University of Rome) -
81
Exploring a variable Newton constant
Modified gravity theories, proposed to address coincidence, cosmological constant problem along with the tensions, often imply a varying Newton constant G. Observational studies usually rely on parametrizations of G, but these can produce quantities, such as the Hubble rate, that are not consistent with Einstein's equations and thus introduce arbitrariness.
We study a more consistent framework based on a minimal extension of General Relativity, where both the cosmological and Newton constants are allowed to vary. This guarantees that the modified Friedmann equations are always satisfied. Using Type Ia Supernovae, Baryon Acoustic Oscillations, Cosmic Chronometers, and strong lensing data, we perform a likelihood analysis and find no evidence for variations in G. We further discuss the results with regard to the circularity problem.Speaker: Dr Fotios Anagnostopoulos (University of Peloponnese) -
82
Cosmological Solutions of a Nonlocal Gravity Model
\begin{equation} S = \frac 1{16\pi G} \int (R-2\Lambda + (R-4\Lambda)\mathcal{F}(\Box)(R-4\Lambda))\sqrt{-g} \mathrm d^4 x \end{equation} was recently introduced, and a few exact cosmological solutions in flat space were presented. One of the solutions has similar properties to an interference between the radiation and the dark energy, while the other one is a nonsingular time symmetric bounce. In this talk we investigate other possible exact cosmological solutions and find some new ones in nonflat space. Used nonlocal gravity dynamics can change background topology. To solve the corresponding equations of motion, we first look for a solution of the eigenvalue problem $\Box (R -4\Lambda) = q (R - 4\Lambda)$. This talk is based on joint work with Branko Dragovich, Zoran Raki\'c and Jelena Stankovi\'c.
Speaker: Prof. Ivan Dimitrijevic (University of Belgrade, Faculty of Mathematics) -
17:20
Coffee Break
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83
Probing cosmic expansion with gravitational wave-large scale structure correlations
The most debated crisis in cosmology today is, perhaps, the inconsistency of the estimated value of the current expansion rate of the Universe (known as the Hubble constant, H0) between different probes using high redshift and low redshift observations. Gravitational wave (GW) emitting sources, which are routinely observed nowadays through the ground-based LIGO-Virgo-KAGRA detector network, could serve as an independent probe shedding light on this crisis. Such sources, also called the "standard sirens", provide us with a direct measure of the cosmological distances through the observed gravitational wave strain. When accompanied by an electromagnetic counterpart, such as Gamma Ray bursts, the redshift of the source can also be determined, thus offering a new avenue to probe the cosmic expansion. However, the majority of the detected GW events are "dark sirens", i.e. they do not have an associated electromagnetic signal. For such sources, one can make use of their clustering properties with respect to the observed galaxies and the underlying dark matter distribution, since they are part of the same large-scale structure and are thus correlated with each other through structure formation history. In this talk, I will discuss how the angular correlation between gravitational-wave standard sirens and galaxies allows an unbiased inference of the Hubble constant. With the growing number of such events in future observations, this technique will be imperative for a robust cosmological inference using GWs.
Speaker: Dr Sayantani Bera (CPT, Aix-Marseille University) -
84
Stochastic scalar field dynamics in dS from quantum deficient oscillators
The stochastic dynamics of a scalar field in dS can be regarded as a non-perturbative diffusion process, to which exact distribution and correlation functions are constructed by utilising the correspondence between diffusion and Schroedinger equations. The Krein--Adler transformation of the quantum harmonic oscillator deletes several pairs of the energy levels to define quantum deficient oscillators, based on which a new class of exact solutions in stochastic inflation is constructed. In addition to the simplest single-well model, our results include models with multiple wells that admit exact solutions.
Speaker: Dr Koki Tokeshi (University of Tokyo) -
85
Dwarf galaxies as dark matter test
In this talk I will give an overview on how the properties of dwarf galaxies have been proved to be in tension with LCDM expectations in terms of their morphology, distribution and phase-space correlation. I will then discuss the different signs of tidal disturbance that the satellite galaxies of the Milky Way present, which can not be explained if these dwarf galaxies are surrounded by a halo of cold dark matter. I will then show that tidal disturbances from the Milky Way gravitational potential are actually expected in MOND for many of these satellite galaxies. The conclusion is that tests on dwarf galaxies repeatedly show that models that assume a LCDM scenario for the formation and evolution of these objects are disfavoured while MOND provides a more natural framework with which to understand their properties. On a cosmological context, this (together with all the well-know tensions faced by LCDM) provides a strong incentive for researchers to explore cosmological models that are based on alternative gravity theories rather than on cold dark matter.
Speaker: Dr Elena Asencio (University of Bonn) -
86
Future Parameter Constraints from Weak Lensing CMB and Galaxy Lensing Power- and Bispectra
Upcoming stage 4 surveys, such as the Simons Observatory, LSST, and Euclid, are poised to measure weak gravitational lensing of the Cosmic Microwave Background (CMB) and galaxies with unprecedented precision. While the power spectrum is the standard statistic used to analyze weak lensing data, non-Gaussianity from non-linear structure growth encodes additional cosmological information in higher-order statistics. We forecast the ability of future surveys to constrain cosmological parameters using the weak lensing power spectrum and bispectrum from both CMB and galaxy surveys, including their cross-correlations. We consider an eight-parameter model ($\Lambda$CDM + $\sum m_\nu$ + $w_0$) and assess constraints for stage 4 survey specifications. In the absence of systematics, both the CMB and galaxy lensing bispectra are found to be detectable at high signal-to-noise. We test two priors: a ''strong" one based on constraints from CMB temperature and $E$-mode polarization anisotropies, and a ''weak" one with minimal assumptions. With the weak prior, the bispectrum significantly improves parameter constraints by breaking degeneracies. For strong priors, improvements are more limited, especially for the CMB bispectrum. On small scales, where non-linear effects dominate, the bispectrum’s constraining power can rival that of the power spectrum. We also find strong synergy between CMB and galaxy lensing; combining both probes leads to tighter constraints, particularly on neutrino mass. It was recently found that the CMB lensing bispectrum is strongly affected by the Born approximation, so we also consider post-Born corrections but find that our main conclusions remain the same. These results highlight the potential of higher-order lensing statistics and motivate further work on neglected effects such as non-Gaussian covariance, instrumental systematics, and baryonic feedback.
Speaker: Dr Jonas Frugte (VSI, Groningen U.)
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70
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09:00
DEPARTURE
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