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GGI workshop: Exploring New Frontiers in Cosmology

→ Europe/Paris
Galileo Galilei Institute

Galileo Galilei Institute

Largo Enrico Fermi, 2 50125 Firenze ITALY
Eleonora Di Valentino (University of Sheffield), Elsa Teixeira (LUPM Montpellier), Luca Visinelli (Università di Salerno & INFN), Matteo Martinelli (INAF - OAR), Vivian Poulin (LUPM (CNRS & U. de Montpellier)), William Giare (University of Hawaii)
Description

The workshop will focus on the current state of cosmology, aiming to address some of its most pressing challenges, identifying key obstacles, and exploring promising opportunities from observational, phenomenological, and theoretical perspectives. Hosted at the Galileo Galilei Institute, the event will centre on two key themes: testing fundamental physics through upcoming cosmological and astrophysical observations, and resolving persistent issues such as cosmological tensions. The timing of the workshop is particularly significant, aligning with the anticipated arrival of extensive data from a wide array of cosmological and astrophysical probes expected in 2026. Participants will have a unique chance to engage with cutting-edge observations, contribute to their analysis and interpretation, and shape the future direction of cosmological research.

Week 1: Introduction and Training Week (6th-10th July)
The first week of the workshop will serve as an introductory training program dedicated to students and early-career researchers, aimed at preparing interested participants who may not be experts on the topic. The focus will be on key cosmological observables relevant to the workshop, methodologies for data analysis, and statistical techniques for comparing theoretical models with observations. The school will include lectures, hands-on tutorials, and discussions. Topics covered will include:
- Statistical and Numerical methods for cosmology;
- Large-scale structure and Baryon Acoustic Oscillations;
- Supernovae cosmology & the Cosmic distance ladder;
- CMB cosmology and next-generation surveys;
- Theory of dark energy and dark matter;
- Cosmology with Gravitational Waves.

Week 2: Observations and Systematics (13th-17th July)
The second week of the workshop will focus on observations and systematics across different surveys and probes, to assess the impact of unknown systematics on current cosmological tensions. We will also consider novel probes that offer independent measurements and may help identify hidden biases in existing methods. Topics covered will include:
- The Hubble tension;
- The role of systematic effects and their impact on cosmological tensions;
- Discussion on alternative cosmological probes;
- Other tensions in cosmological data;
- Future outlook: new observables, new surveys, new ideas.

Week 3: Conference Week (20th-24th July)
The third week of the workshop will host a conference focused on new frontiers and emerging directions in cosmology, astrophysics, and astroparticle physics, in light of the wealth of data collected over the past decade. Special emphasis will be given to the interplay between these observations and our understanding of fundamental physics. Topics to be addressed during the conference include
- Inflation;
- Dark Matter;
- Dark Energy;
- Extensions to the Standard Model of particles and their implications for cosmology;
- Modified Gravity Theories and their implications for cosmology.

Week 4: Models and Methods (27th-31st July)
This final week of the workshop is designed to synthesize the key outcomes of the previous sessions, with a focus on the observational tensions discussed throughout. We will examine the most compelling alternative theoretical scenarios proposed to simultaneously explain recent measurements, cosmic tensions, and possible hints of new physics. Topics covered during this week include:
- Review of observational evidence for deviations from ΛCDM;
- Overview of theoretical alternatives and model comparison techniques;
- Model-independent tests of ΛCDM;
- Emerging statistical techniques.

 

Organisers:

  • Eleonora Di Valentino (School of Mathematical and Physical Sciences, The University of Sheffield)
  • William Giarè (Department of Physics and Astronomy, University of Hawaii)
  • Matteo Martinelli (INAF, Osservatorio Astronomico di Roma)
  • Vivian Poulin (Laboratoire Univers & Particules de Montpellier, Université de Montpellier, CNRS)
  • Elsa Teixeira (Laboratoire Univers & Particules de Montpellier, Université de Montpellier, CNRS)
  • Luca Visinelli (Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno)
Map_GGI.pdf
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  • lun. 6 juillet
  • mar. 7 juillet
  • mer. 8 juillet
  • jeu. 9 juillet
  • ven. 10 juillet
    • Dark Energy and Modified Gravity: Hands-on Session

      Lecture

      Président de session: Alessandra Silvestri (Leiden University)
    • 10:30
      Coffee Break
    • Cosmology with Gravitational Waves: Hands-on Session
      Président de session: Antonella Palmese (Carnegie Mellon University)
      Gravitational_Wave_Cosmology_GGI_2026_Lec1.pdf
      GW Cosmology GGI - Lecture 2.pdf
      GW Cosmology GGI - tutorials.pdf
    • 12:30
      Lunch
    • Student Talks: Session 1
      • 1
        Cosmology with Torsion and Nonmetricity

        Metric affine gravity (MAG) represents an extension of general relativity (GR) in which an independent connection other than the Levi-Civita one is present. In MAG there are three tensors describing the geometry of spacetime, curvature, torsion and nonmetricity. And two tensors related to matter's behaviour, the stress energy tensor and the hypermomentum. After reviewing the main features of metric affine gravity, I will show how MAG changes the GR predictions for cosmology.

        Orateur: Ilaria Andrei
        Ilaria_Andrei.pdf
      • 2
        Inverse non-metricity in f(Q) gravity: cosmology and observational constraints

        In this talk I will present a minimal modified gravity model within the symmetric teleparallel formulation, based on an inverse non-metricity term that introduces no additional free parameters with respect to $\Lambda$CDM. I will discuss its main cosmological signatures as well as observational constraints obtained from CMB data alone and in combination with BAO, RSD, SNIa, and DES data, considering both fixed minimal neutrino mass and varying $\Sigma m_\nu$. Although the model can favor higher values of $H_0$ than $\Lambda$CDM, late-time observations place strong constraints on its viability as a minimal alternative to dark energy.

        Orateur: Simão Marques Nunes (Institute of Astrophysics and Space Sciences (Lisbon Portugal))
        SMN_Talk.pdf
      • 3
        Revisiting Quadratic Scalar Field (Fuzzy, Wave, Ultralight) Dark Matter in Light of DESI DR2 and Current Cosmological Observations

        We study the cosmological phenomenology of quadratic scalar field dark matter (SFDM) using an implementation in the Boltzmann code CLASS, in which dark matter is modeled as a single ultra-light scalar field with potential V (ϕ) = 12 m2ϕ ϕ2 . Adopting a dynamical-systems approach, we analyze the expansion of the homogeneous scalar field together with its linear perturbations, enabling stable numerical predictions for the relevant cosmological observables. We derive the CMB temperature anisotropy spectrum and the linear matter power spectrum, verifying the numerical stability of our implementation across the parameter space. We constrain the model with Planck 2018 CMB data, DESI DR2 BAO measurements, the three-dimensional Lyman-α forest matter power spectrum, and the Pantheon+ supernova compilation. We find that the standard cosmological parameters remain close to their ΛCDM counterparts, with no clear departures from the concordance scenario. For the scalar-field mass, the baseline dataset combination yields an essentially flat posterior over the explored range. The inclusion of Lyman-α information introduces non-trivial structure in the marginalized posterior, which becomes broad and non-unimodal and allows us to derive a one-sided 95% C.L. lower bound of log10 (mϕ /eV) > −22.15. These results show that the quadratic single-field SFDM scenario remains observationally viable and motivate further discussion of the phenomenological implications associated with the allowed ultra-light mass range.

        Orateur: Hafiz Inam ullah (ESFM - Escuela Superior de Física y Matemáticas - IPN)
        Hafiz-Inamullah2.pdf
      • 4
        Taming Instabilities in Mass-Varying Neutrino Cosmology

        Mass-varying neutrino models with strong scalar couplings are typically affected by late-time perturbative instabilities. In this talk, I present an inverse symmetron-like phase transition in which the neutrino nonrelativistic transition activates the fifth force, while the subsequent dilution of the neutrino density restores the symmetry and suppresses the coupling. This mechanism avoids excessive linear growth at late times and can generate a transient early dark energy component near recombination, with possible implications for the Hubble tension.

        Orateur: Vitor da Fonseca (Institute of Astrophysics and Space Siences (Lisbon, Portugal))
        neutrino_cosmology.pdf
      • 5
        Cosmic Birefringence and Axion Dark Energy

        Recent analyses of Planck polarization data have reported a hint of cosmic birefringence at the level of a $~3.6\sigma$ deviation from the parity-conserving standard cosmological model. At the same time, tensions between CMB data and large-scale structure observations can be alleviated by replacing the cosmological constant with dynamical dark energy. Ultralight axion-like particles can explain both signals by rotating the polarization plane of CMB photons and contributing to the background evolution via a time-varying equation of state.

        In this talk, I will present a modified version of the Einstein-Boltzmann solver CLASS that self-consistently calculates parity-odd CMB power spectra for an axion dark energy model with a quadratic potential. This will, for the first time, allow a unified treatment that tracks the late-time evolution of the pseudo-scalar field and simultaneously predicts its impact on cosmological observables. I will show how different axion masses produce distinctive features in the CMB polarization power spectra.

        Orateur: Lena Stefanie Scheuchl (Max Planck Institute for Astrophysics)
        GGI_2026_Scheuchl.pdf
      • 6
        Constraining DDE Models with AdS-to-dS and Similar Late-Time Transitions

        With the release of DESI DR2, dynamical dark energy (DDE) models gained unprecedented attention as model candidates to release the current cosmological tensions. However, majority do not perform well in relaxing the H0 tension compared to some of the other novel theoretical and phenomenological DE models in the literature, such as the LsCDM model that can be explained by an AdS-to-dS transition in the late times. My work focuses on the data analysis of models that combine the features of DDE models with transition scenarios to potentially address, foremost, the H0 and other cosmological tensions.

        Orateur: Mine Gökçen (Istanbul Technical University)
        GGI_studenttalk_MG.pdf
      • 7
        Understandig the Dark Sector through reconstructions

        Within the standard understanding of cosmology, the existence of Dark Matter and Dark Energy is considered. Together, these constitute approximately 95% of the Universe; however, their behavior is not fully understood. Through reconstructions, the phenomenological behavior of both Dark Energy and Dark Matter can be inferred from astronomical observations. This work addresses the interpolation method for reconstructing the Equation of State $\omega(z)$ and the normalized energy density $f(z)=\frac{\rho(z)}{\rho_0}$, which is used to study Dark Energy on its own and the Dark Sector (Dark Energy and Dark Matter) as a whole.

        Orateur: David A López Magaña (Universidad Nacional Autónoma de México)
        GGI - Understandig the Dark Sector through reconstructions.pdf
      • 8
        Reconstructing dark energy with fewer assumptions

        We perform minimalistic reconstructions of the dark energy density and equation of state using late-time distance measurements. Our methodology avoids assumptions that correlate the values of these functions over time and instead yields their approximate average evolution within seven redshift bins from z=0 to z=4.2. Constraints are obtained using combinations of baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument (DESI) or the completed Sloan Digital Sky Survey (SDSS), alongside Type Ia supernovae measurements from Pantheon+ or the latest recalibrated samples, Union3.1 or DES-Dovekie. Only an acoustic scale prior is included from the Cosmic Microwave Background so that our results are insensitive to the possible matter density tension between early and late-time probes. All combinations yield consistent reconstructed histories: a dark energy density that rises to a local maximum before decreasing at late times and an equation of state with two apparent oscillations around the cosmological constant limit. These patterns are robust to numerous parameter extensions, such as freely varying spatial curvature and neutrino mass, and they persist in the uncorrelated amplitudes obtained through localized principal component analysis. Our results suggest that dark energy evolution is a persistent preference of the late-time distance measurements.

        Orateur: Daniel Kessler (University of Sheffield)
        Reconstructing dark energy with fewer assumotions - GGI July 2026.pdf
      • 9
        Multi-field early dark energy and the Hubble tension

        Early dark energy (EDE) is a popular extension of the $\Lambda$CDM model, which alleviates the Hubble tension by reducing the sound horizon at recombination. The updated Planck high-$\ell$ likelihood (NPIPE), however, places strong constraints on such models.

        In this talk, I will present a model with two non-interacting EDE fields active at different redshifts, inspired by the string Axiverse. Compared to standard EDE, the extra freedom in the two-field model allows the energy boost to spread out over a broader redshift range, which results in an improved fit to high-$\ell$ Planck NPIPE data and, in turn, reduces the Hubble tension. I will also show models with more than two fields, to highlight the statistical artifacts of adding too many degrees of freedom.

        The main takeaway is this: in light of Planck NPIPE, a rich pre-recombination history, whether it be 2-field EDE or something else, is an interesting contender for the Hubble tension.

        Orateur: Marco Bella (University of Trento)
        mEDE_and_H0_split_v3.pdf
        mEDE_and_H0_v3.pdf
      • 10
        Non-linear structure of interacting dark energy model

        Following our previous work constraining interacting dark energy (IDE) models, which showed their potential to alleviate the Hubble tension, in this work we investigate the non-linear effects of the IDE scenario favoured by CMB and DESI observations. The implications of IDE for the $S_8$ tension remain unclear, since current weak-lensing and large-scale-structure analyses either exclude highly non-linear scales or model the non-linear regime using prescriptions calibrated within $\Lambda$CDM. We address this issue by implementing a fully self-consistent IDE pipeline. We perform N-body simulations of the IDE model with a transfer rate $Q=\xi\mathcal{H}\rho_{DE}$ using a modified implementation of RAMSES. Since the dark matter Euler equation remains unchanged with respect to ΛCDM, the interaction can be incorporated through the modified background evolution and an effective time-dependent dark matter particle mass. We find scale-dependent deviations in the quasi-linear and non-linear regimes of the matter power spectrum, together with modifications to the density-field morphology and halo abundance. Our results show that the impact of IDE on quasi-linear and non-linear structure formation cannot be captured by standard $\Lambda$CDM-calibrated prescriptions, highlighting the importance of model-consistent non-linear modelling for future weak-lensing and large-scale-structure constraints on interacting dark energy cosmologies.

        Orateur: Yuejia Zhai (University of Sheffield)
        GGIweek1 - Zhai.pdf
    • 15:40
      Coffee Break
    • Student Talks: Session 2
      • 11
        Likelihood-Ratio Tests with Correlated Parameter Boundaries: Implications for CMB B-mode Searches

        Likelihood-ratio statistics play a central role in assessing detection significance in cosmological analyses. Under regularity conditions, Wilks’ theorem predicts that these statistics follow a $\chi^2$ distribution in the asymptotic limit. When a parameter is restricted to a physical boundary, this result no longer holds, and Chernoff’s theorem provides the corresponding mixed distribution. In practice, however, cosmological likelihoods often involve several parameters that are both bounded and strongly correlated, and the extent to which standard asymptotic results apply in these settings remains unclear.
        In this work, I investigate how parameter correlations and positivity constraints modify likelihood-ratio statistics in the context of CMB B-mode searches. These analyses typically involve the tensor-to-scalar ratio together with foreground amplitudes that are physically required to be non-negative, leading to a likelihood geometry that differs from the assumptions underlying the usual asymptotic results. Using simplified likelihood models, I examine the behaviour of profile likelihoods and likelihood-ratio tests in the presence of such correlated boundaries.
        The results reproduce qualitative features seen in recent CMB analyses, where the empirical distribution of likelihood-ratio statistics deviates from the standard Chernoff prediction. I show that correlations between bounded parameters modify the probability that the likelihood peaks at the boundary, thereby altering the expected survival curves used to assess detection significance.
        Understanding these effects is important for interpreting likelihood-ratio tests in current and upcoming high-precision CMB experiments, where increasingly sensitive measurements make the statistical behaviour of constrained likelihoods particularly relevant.

        Orateur: Georgia Kiddier (DAMTP, University of Cambridge)
        ggi_presentation.pptx
      • 12
        Cosmic birefringence from a stiff axion-like field

        When polarized electromagnetic radiation propagates through a region of space permeated by a pseudo-scalar field, the plane of linear polarization undergoes a rotation. The rotation angle depends on the field's values when the radiation is emitted and when it is detected and does not depend on the frequency of the radiation. This phenomenon is called Cosmic Birefringence (CB) and is usually studied for CMB photons in the context of axion dark matter and axion dark energy.
        We propose a new explanation in terms of a stiff (w=1) pseudo-scalar field that constitutes a now-subdominant component of the total energy density of the Universe. We find a very narrow range for the axion-photon coupling and we predict a very distinctive dependence of the birefringence angle on the redshift. We show that our model can produce signatures in the stochastic gravitational-wave background for which the Pulsar Timing Array (PTA) collaborations found first evidence in 2023.

        Orateur: Andrea Minotti
        GGI_Andrea_Minotti.pdf
      • 13
        On the potential of pseudo-scalar dark energy

        A cosmological pseudo-scalar field provides a compelling realization of dynamical dark energy (DE). If its coupling to photons is non-negligible, the cosmic microwave background acquires a rotation of its polarization plane, known as cosmic birefringence (CB). We present an extended analysis of several pseudo-scalar DE models and derive constraints on the parameters of their potentials by combining observations of the background expansion history with measurements of CB. We find that the axion-like potential constitutes a viable model only for large values of the anomaly coefficient.
        Scenarios in which the pseudo-scalar field rolls down a potential with quadratic, linear, or Ratra-Peebles forms can successfully explain DE and CB, with a symmetry-breaking scale close to the GUT scale.

        Orateur: Yunzhi Wu (UniTo and INFN)
        GGI3.pdf
      • 14
        CMB spectral distortion anisotropies from photon to dark photon conversions

        Distortions of the CMB power spectrum have been proven to be a powerful probe for several cosmological and astrophysical processes. The energy distribution of the photons could provide complementary information to the well-studied temperature anisotropies, directly accessing pre-recombination physics. Each process releasing energy or changing the photon number density through the history of the Universe has left an imprint on the CMB, allowing for the possibility of putting constraints. Most previous studies focused on the monopole component only, but recently a framework has been developed that generalises the usual computation of CMB temperature and polarisation anisotropies. In our work, we used this new system of equations, implemented into the code CosmoTherm, to put limits on photon-to-dark-photon conversions. In this talk, after a brief introduction on the field, I will present this new framework and the computed transfer functions and cross-correlated power spectra. We were also able to place complementary limits on the dark photon model parameters using Planck data, finding constraints only marginally weaker than those obtained with COBE/FIRAS for the monopole distortion.

        Orateur: Sara Evangelista (University of Manchester)
        Evangelista-GGI.pdf
      • 15
        Constraining Primordial Magnetic Fields using Rayleigh Scattering of CMB

        The presence of magnetic fields has been inferred in extragalactic spaces like voids, and astrophysical mechanisms are unable to explain the magnitude of these fields. This hints towards cosmological magnetic fields of primordial origin, that are amplified by the astrophysical dynamo effect.

        As future surveys and telescopes provide higher precision measurements of CMB, LSS and EoR; we are expected to constrain the strength of these Primordial Magnetic fields (PMFs), if not detect them. However, addition of PMFs leads to effects that differ from the standard $\Lambda$-CDM predictions on which our inferences are based.

        One important effect of PMFs is on recombination and the CMB. The presence of PMFs leads to additional clumping in the pre-recombination plasma, accelerating the recombination process. As a result, the inferred angular diameter distance to last scattering increases, and our inference of cosmological parameters changes. For example, the measured $H_0$ increases in a universe with PMFs, likely alleviating the Hubble tension.

        The CMB photons scatter with neutral H (and He) atoms post recombination, prolonging last scattering. Since this effect is based on well-understood physics, it provides a robust probe of the ionization history and the last scattering surface. Thus, measuring Rayleigh scattering of the CMB would help constrain the ionization history and indirectly constrain PMFs.

        My project deals with combining both effects and presenting realistic estimates of the constraints obtainable from CMB observations from the Simons Observatory, CCAT Observatory, and Planck Collaboration.

        Orateur: Kwanit Gangopadhyay (University of Groningen)
        Kwanit.key
      • 16
        Exploring the Lyman-Alpha Forest in a Dynamical Dark Energy Cosmology using Cholla

        The Dark Energy Spectroscopic Instrument (DESI) Collaboration, when combining their baryonic acoustic oscillation observations with measurements of supernova surveys and cosmic microwave background data, inference of a best fit cosmology with a time-varying dark energy motivates independent observational tests of a departure from a cosmological constant dark energy. I will discuss the results of a limited set of hydrodynamic cosmological simulations on how a dynamical dark energy component may imprint itself on the Lyman Alpha forest of neutral hydrogen absorption. In comparing a dynamical dark energy cosmology of the kind inferred by the DESI Collaboration to one evolved with a cosmological constant, we find a redshift-dependent spectral tilt in the transmitted flux power spectrum. These dynamical dark energy models exhibit a slightly warmer intergalactic medium and a lower Lyman Alpha optical depth.

        Orateur: Diego Garza (University of California, Santa Cruz)
        Garza_GGI_2026_PDF.pdf
      • 17
        Dark energy, spatial curvature, and star formation efficiency from JWST photometric and spectroscopic high-redshift galaxies

        Early observations from the James Webb Space Telescope (JWST) have revealed an overabundance of massive high-redshift galaxies, raising the question of whether this points to new physics beyond ΛCDM, or an enhanced formation efficiency of massive stars. In this talk, I will present a Bayesian analysis of the most massive galaxies identified in recent JWST photometric and spectroscopic surveys, jointly constraining cosmological parameters and the baryon-to-star conversion efficiency. I will discuss the impact of extensions to the standard ΛCDM model, allowing the dark energy equation of state and spatial curvature to vary. Our results show no evidence for deviations from ΛCDM and suggest that the origin of the “JWST tension” is more likely related to astrophysical processes governing galaxy formation than to modifications of the cosmological model.

        Orateur: Leonardo Comini
        GGI talk - Leonardo Comini.pdf
      • 18
        Measuring the Expansion Rate of the Universe with Strong Gravitational Lenses

        Strong gravitational lensing serves as a powerful, independent probe for measuring the Hubble constant (H0). We present the framework of time-delay cosmography and its relevance to the ongoing Hubble tension. We present the procedure for end-to-end cosmographical analysis. We then present ongoing mass-modelling efforts for two systems: the quadruply lensed quasar J1537-3010 and Supernova Winny (SN 2025wny). This work establishes the lens models that will be the foundation for future time-delay cosmography with these systems.

        Orateur: Allan Gabriel Schweinfurth Pupo (Technical University of Munich / Max Planck Institute for Astrophysics)
        GGI_SummerSchool.pptx
      • 19
        Galaxy clusters as cosmic lenses for high frequency gravitational-waves

        High-frequency Gravitational Waves~(HFGW) ($f \gtrsim 1$ MHz) offer a distinctive probe of exotic physics and early-Universe cosmology. In the absence of dedicated detectors targeting this frequency range, indirect probes based on graviton–photon conversions in astrophysical magnetic fields become particularly relevant. In this talk we show that the extended magnetic fields permeating Galaxy Clusters may act as cosmic lenses, leading to a strong enhancement of graviton-photon conversions. In this context, X- and $\gamma$-ray observations of the Virgo Cluster through large field-of-view instruments such as eROSITA and COMPTEL yield novel limits on the amplitude of stochastic HFGW backgrounds in the frequency range $10^{17}-10^{22}$~Hz, improving upon constraints derived from the Galactic magnetic field by one to two orders of magnitude.

        Orateur: Tiziano Zanzarella
        Zanzarella_GGI_HFGW.pdf
      • 20
        Constraining the lensing dispersion from the angular clustering of binary black hole mergers

        Gravitational waves from inspiraling compact binaries provide direct measurements of luminosity distances and serve as a powerful probe of the high-redshift Universe. In addition to their role as standard sirens, they offer an opportunity to constrain small-scale density fluctuations through the dispersion in the distance-redshift relation induced by gravitational lensing. In this talk, we propose a method to constrain this lensing dispersion without requiring redshift information by analyzing the angular clustering of gravitational-wave sources. Our formalism, which incorporates second-order lensing effects in the luminosity distance, shows that the amplitude of the auto-correlation angular clustering decreases with increasing lensing dispersion. While we demonstrate that the auto-correlation signal is detectable with sufficient signal-to-noise ratios in future gravitational wave experiments, a strong degeneracy exists between the lensing dispersion and the linear bias of gravitational wave sources. We demonstrate that this degeneracy is partially broken by a joint analysis of the autocorrelation of gravitational wave sources and the cross-correlation with galaxies whose redshifts are known.

        Orateur: Fumihiro Chuman (Chiba Universitty)
        F_chuman.pdf
  • lun. 13 juillet
    • Registration
    • 21
      Time-delay cosmography with strongly lensed quasars: current results and future prospects

      Time-delay cosmography with strongly lensed quasars provides a direct, one-step measurement of the Hubble constant in the local Universe, independent of the cosmic distance ladder and early-Universe probes. By measuring the time delays between multiple images of a variable background quasar, and modeling the gravitational potential of the deflector galaxy, one can infer absolute distances that scale inversely with the Hubble constant. This technique therefore offers a powerful and complementary approach to addressing the current tension in measurements of H0.
      In this talk, I will present updated cosmological constraints from strongly lensed quasars based on a new analysis by the TDCOSMO collaboration. We combine high-resolution imaging from the James Webb Space Telescope (JWST), spatially resolved stellar kinematics of the lens, and improved treatments of line-of-sight effects to refine our models of the deflector galaxies. In particular, we implement a framework that fully accounts for the mass-sheet degeneracy in the lens mass density profile. This degeneracy is constrained using new stellar velocity dispersion measurements from JWST resolved spectroscopy. These advances significantly reduce key systematic uncertainties and strengthen the robustness of time-delay cosmography as a precision probe of late-time cosmology. This talk will be given on behalf of the TDCOSMO collaboration.

      Orateur: Martin Millon (University of Geneva)
    • 10:45
      Coffee break
    • 22
      Alternative routes to H0: time-delay cosmography with lensed SNe and the tailored expanding photosphere method for SNe II

      In this talk, I will present two indepent local techniques to measure the Hubble constant.
      Time-delay cosmography with strongly lensed SNe has first been proposed more than 60 years ago, but has become feasible only very recently with the machine-learning aided compilation of large catalogues of strong lenses and the advent of telescopes/surveys such as Euclid, Rubin LSST, ZTF, and JWST. I will review the status of the field with a particular emphasis on the efforts by the HOLISMOKES collaboration, and focus on the exciting lensed SNe Winny and Requiem, which will provide H0 measurements with competitive errors in the near future.
      Lately celebrating its 50th birthday, the expanding photosphere method for Type II SNe is barely younger than time-delay cosmography. Also this method has only become competitive in recent years thanks to computational advances and the use of spectral emulators. These allow us to replace the previously employed pre-computed dilution factors by individually optimised radiative-transfer models for every SN to infer its luminosity and distance. I will discuss the results from a pilot study based on literature data of SNe II, as well as preliminary results from the dedicated adH0cc programme.

      Orateur: Stefan Taubenberger
    • 12:30
      Lunch
    • 23
      SH0ES
      Orateur: Adam Riess (online)
    • 15:15
      Coffee Break
    • Discussion
  • mar. 14 juillet
    • 24
      The TRGB and JAGB Distance Scales: Current Status, Systematics, and the Hubble Constant

      The tension between early- and late-universe determinations of the Hubble constant has placed extraordinary demands on the precision and accuracy of the extragalactic distance ladder. I review the current status of two standard candles - the Tip of the Red Giant Branch (TRGB) and the J-region Asymptotic Giant Branch (JAGB) - as independent calibrators of Type Ia supernovae. For each method, I discuss theoretical foundations, systematic error budgets, and recent observational progress enabled by HST and JWST. I then compare TRGB- and JAGB-based H0 determinations to one another and to Cepheid-based results, and conclude with a discussion of outstanding systematics and priorities for the field.

      Orateur: Siyang Li (online) (University of California, Berkeley)
    • 10:45
      Coffee break
    • 25
      Current status of type Ia supernova cosmology
      Orateur: Lluís Galbany (ICE-CSIC)
    • 12:30
      Lunch break
    • 26
      The present and the future of quasars in cosmology

      I will review what the prospects of quasars in the context of observational cosmology are and I will present recent measurements of the expansion rate of the Universe based on a Hubble diagram of quasars detected up to the highest redshift ever observed (z~7.5).
      The derived distances are in agreement with the standard flat LCDM model up to redshift of ~1.5, but they show significant deviations at higher redshifts. Yet, several authors suggested that this discrepancy is due to inconsistencies between the low- and high-redshift sources within the parent sample, or to a redshift evolution of the relation. I will discuss these issues through a quantitative comparison with supernova-derived distances in the common redshift range, complemented by simulations showing that all the claimed inconsistencies would naturally arise from any limitation of the cosmological model adopted for the data analysis, that is, from our ignorance of the 'true' cosmology.
      I will finally show that the synergy amongst multi-wavelength facilities (current and future) will provide the needed sample statistics to obtain constraints on the observed deviations from the standard cosmological model which will rival and complement those available from the other cosmological probes.

      Orateur: Elisabeta Lusso
    • 15:15
      Coffee Break
    • Discussion
  • mer. 15 juillet
    • 27
      KiDS-Legacy: Final cosmological constraints from the complete Kilo-Degree Survey

      The Kilo-Degree Survey (KiDS) provides some of the most precise measurements of weak gravitational lensing, enabling stringent constraints on the cosmological model from wide-field imaging data. In this talk, I will discuss the key methodological developments with respect to earlier KiDS analyses, and present the latest cosmological constraints from the fifth and final KiDS data release. I will then discuss the updated KiDS-Legacy results in light of the apparent $S_8$ tension between probes of the early and late Universe. Additionally, I will review tests of the internal consistency of the KiDS-Legacy dataset and summarize results from follow-up projects exploring extensions to the standard cosmological model. Finally, I will give an outlook on upcoming analyses of cosmic shear combined with galaxy clustering and galaxy-galaxy lensing with KiDS.

      Orateur: Dr Benjamin Stölzner (Ruhr University Bochum)
    • 10:45
      Coffee break
    • 28
      Weak lensing: what's next?

      Stage-III galaxy surveys have shown that weak lensing, and combined 3x2pt analyses, can provide exquisite constraints on the dark components of the Universe. Following a successful launch in July 2023 and the start of its scientific survey in February 2024, Euclid has become the first stage-IV photometric survey in operations. This marks the start of even more exciting science from weak lensing analyses using stage-IV data. In this talk I will present the forecasts for weak lensing and combined analyses at the end of stage-IV missions, focusing in particular on how combining multiple probes helps break parameter degeneracies and leads to tighter constraints on the cosmological model under investigation. I will conclude by outlining the current efforts toward a combined analysis with Euclid's first data release.

      Orateur: Isaac Tutusaus (ICE/IRAP)
    • 12:30
      Lunch break
    • 29
      Reconstructing the Universe using Peculiar Velocities of Type Ia Supernovae

      Cosmology is the study of the origin, composition, evolution, and ultimate fate of the Universe. In recent decades, there have been significant advances in both the observational and theoretical aspects of our understanding of the Universe. The study of Type Ia Supernovae (SNe Ia) has been instrumental in driving this progress. Despite these advances, many questions in cosmology remain open. In this talk, I show that the peculiar velocities of SNe Ia can be used to reconstruct both the local Universe and its expansion history, and I highlight current and future opportunities in light of upcoming large-scale surveys such as the LSST, which is expected to discover an unprecedented number of SNe Ia.

      Orateur: Francesco Sorrenti (ICC - University of Barcelona)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • jeu. 16 juillet
    • 30
      LSS beyond the BAO
      Orateur: Marko Simonovic
    • 10:45
      Coffee break
    • 31
      DES
      Orateur: Marco Raveri (University of Genova)
    • 12:30
      Lunch Break
    • 32
      Particle cosmology in the era of tensions

      Cosmology is one of the most promising avenues to learn about fundamental properties of the building blocks of the Universe. In particular, new-generation experiments will transform the search for light relics, including neutrinos. In this talk, I will give an overview of where we stand and some thoughts on how to move forward as intriguing discrepancies between standard model predictions, laboratory searches and cosmological data emerge.

      Orateur: Martina Gerbino (INFN Ferrara)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • ven. 17 juillet
    • 33
      CMB: a global view
      Orateur: Lloyd Knox
    • 10:45
      Coffee break
    • 34
      Modified recombination meets the Hubble tension

      The recombination history of the universe is one of the crucial theoretical ingredients for the computation of the CMB temperature and polarization power spectra. In this talk, I will discuss this link and show how modified recombination scenarios help alleviate the Hubble tension. Beyond changes to the average recombination history I will also consider transport corrections in the clumpy universe at recombination and then discuss how we might be able to directly probe the recombination process with future CMB spectrometers.

      Orateur: Jens Chluba (JBCA)
    • 12:30
      Lunch Break
    • 35
      Dark Energy: what's next?

      The nature of dark energy remains one of the most profound open questions in modern cosmology. Despite two decades of increasingly precise observations, the standard cosmological model—anchored by a cosmological constant—continues to provide an excellent phenomenological fit, while raising deep theoretical tensions. As we enter the era of high-precision large-scale structure surveys, led by missions such as Euclid, we are poised to move beyond parameter estimation into a regime of model discrimination and discovery.
      In this talk, I will discuss the next frontier in dark energy research from both theoretical and data-driven perspectives. I will highlight how advances in modeling of large-scale structure observables, combined with next-generation inference pipelines, are reshaping our ability to test extensions beyond ΛCDM. Emphasis will be placed on the role of effective field theory approaches, novel observables, and the integration of machine learning techniques to accelerate Bayesian inference and capture non-linear structure formation.
      I will present recent developments in the construction and validation of end-to-end cosmological pipelines within the Euclid Science Ground Segment, and discuss how upcoming data releases will enable stringent constraints on dynamical dark energy, modified gravity, and beyond-standard paradigms. Finally, I will outline the key theoretical and computational challenges that must be addressed to fully exploit this new data landscape, and argue that the coming decade will be defined not only by precision cosmology, but by our ability to robustly interpret it.

      Orateur: Guadalupe Cañas-Herrera
    • 15:15
      Coffee Break
    • Discussion: TBD
  • lun. 20 juillet
    • Registration
    • Welcome
      Présidents de session: Dr Eleonora Di Valentino (University of Sheffield), Elsa Teixeira (LUPM Montpellier), Luca Visinelli (Università di Salerno & INFN), Matteo Martinelli (INAF - OAR), Dr Vivian Poulin (LUPM (CNRS & U. de Montpellier)), William Giare (University of Hawaii)
    • 36
      Cosmology at the Crossroads: Puzzles and Perspectives

      Cosmology is arguably the most captivating field in physics today. Its unique appeal lies not only in how it integrates all fields of physics, but also but also in the close relationship between theory and observation. Enormous progress has been made and is still to be expected in cosmological observations. For theorists, the primary challenge remains: how can we best leverage these observations to resolve the fundamental puzzles of our universe?

      In my talk, I shall briefly recapitulate what we have learned about our Universe before introducing the most pressing outstanding questions.
      I shall also discuss some present leads we have that may help us address these mysteries and explore how future observations will drive our progress.

      Orateur: Prof. Ruth Durrer (DPT Université de Genève)
    • 10:30
      coffee break
    • 37
      Invading Florence with Elephants Across the Phantom Divide

      Cosmological data indicates that dark energy was phantom (w<-1) above
      z=1, rapidly evolved across the phantom divide (w=-1), and today has w>-1.
      These properties may arise from different dark components (a chimera) or
      have a unified origin (an elephant - a single animal despite scientists
      in the dark guessing a snake for the trunk, tree trunks for the legs, etc).
      I describe ideas for dark energy elephants, and which falter, just as few
      of Hannibal's elephants survived crossing the Alps to reach Florence.

      Orateur: Eric Linder (LBL)
    • 38
      Stress-Testing the Universe with CMB Spectral Distortions

      TBA

      Orateur: Bryce Cyr (brycecyr@mit.edu)
    • 12:30
      lunch break
    • 39
      AGN Variability in the Survey Era: From Accretion-Disk Physics to Cosmological Distances

      Large time-domain surveys are turning AGN variability into a population-scale probe of both supermassive black-hole accretion and cosmology. UV/optical variability depends on rest-frame timescale, wavelength, and luminosity: at fixed wavelength and time lag, more luminous sources vary less. This luminosity anti-correlation motivates Type 1 AGN variability as a potential distance indicator beyond the redshift range densely populated by Type Ia supernovae, offering an independent route to test the expansion history at high redshift.
      I will present a hierarchical Bayesian framework that combines Gaussian-process modelling of AGN light curves with joint inference of variability-luminosity population parameters and cosmology. The method propagates source-level light-curve uncertainties into a population model relating variability to luminosity, rest-frame wavelength, intrinsic scatter, selection, and the assumed distance-redshift relation. Survey-like mock catalogues are used to validate the inference pipeline and quantify the impact of finite baselines, magnitude limits, chromatic variability, and calibration degeneracies.
      I will discuss applications to Gaia G-band and ZTF g/r-band light curves for ∼200,000 SDSS AGN, highlighting current constraints, key degeneracies, and the role of multi-band data in separating luminosity, wavelength, and cosmological effects. I will close with prospects for AGN variability cosmology with Gaia DR4, DESI-selected AGN, and Rubin/LSST-era time-domain surveys.

      Orateur: Júlia Laguna I Miralles (University of Cambridge)
    • 40
      Coupled Dark Energy and Dark Matter for DESI: An Effective Guide to the Phantom Divide

      Motivated by the recent Dark Energy Spectroscopic Instrument (DESI) DR2 preference for dynamical dark energy, we study interacting dark energy models in which a canonical quintessence field couples to cold dark matter through a field-dependent mass $m(\phi)$. In such scenarios, the effective equation of state inferred under the assumption of non-interacting dark sectors, $w_{\rm eff}(z)$, can differ from the intrinsic scalar-field equation of state $w_\phi(z)$, making an apparent phantom crossing $w_{\rm eff}<-1$ possible without introducing a phantom scalar. We show that a viable realization of this mechanism requires the scalar field to originate from a frozen phase deep in the radiation era, in order for the effective coupling to remain sufficiently suppressed before recombination to evade cosmic microwave background constraints, and for the late-time evolution to become strong enough to reproduce the apparent behavior of $w_{\rm eff}(z)$ preferred by DESI. We identify the general conditions that allow these requirements to be satisfied simultaneously, and present an illustrative phenomenological realization in which $w_{\rm eff}(z)$ evolves from $w_{\rm eff}\approx -1.2$ at $z \approx 1.0$ to $w_{\rm eff}\approx -0.9$ at $z\approx 0.4$. These conditions and requirements serve as a guide for designing future models of this kind which can safely navigate the phantom divide at $w=-1$ in an effective way without phantom fields.

      Orateur: Stephen King (University of Southampton)
    • 41
      Dark Energy and Modified Gravity in the DESI Era: Breaking Degeneracies with Multi-Probe Strategies

      The recent Baryon Acoustic Oscillation measurements from the Dark Energy Spectroscopic Instrument (DESI) reveal persistent tensions in modern cosmology, including hints of dynamical dark energy evolution and neutrino mass constraints so stringent they conflict with oscillation experiments. A fundamental challenge is that theoretically distinct models produce nearly indistinguishable expansion histories while differing in their underlying microphysics and gravitational couplings. Breaking model degeneracies requires combining multiple independent observational probes to distinguish among alternative dark energy and modified gravity theories.

      In this talk, I will review how current cosmological tensions interconnect and present multi-probe strategies to address them. I will discuss constraints on alternative cosmological models in light of DESI results, and highlight synergies with future gravitational wave detectors.

      Orateur: Andrea Cozzumbo (GSSI - Gran Sasso Science Institute)
    • 42
      Non-linear effects of interacting dark energy model

      Following our previous work constraining interacting dark energy (IDE) models, which showed their potential to alleviate the Hubble tension, in this work we investigate the non-linear effects of the IDE scenario favoured by CMB and DESI observations. The implications of IDE for the $S_8$ tension remain unclear, since current weak-lensing and large-scale-structure analyses either exclude highly non-linear scales or model the non-linear regime using prescriptions calibrated within $\Lambda$CDM. We address this issue by implementing a fully self-consistent IDE pipeline. We perform N-body simulations of the IDE model with a transfer rate $Q=\xi\mathcal{H}\rho_{DE}$ using a modified implementation of RAMSES. Since the dark matter Euler equation remains unchanged with respect to $\Lambda$CDM, the interaction can be incorporated through the modified background evolution and an effective time-dependent dark matter particle mass. We find scale-dependent deviations in the quasi-linear and non-linear regimes of the matter power spectrum, together with modifications to the density-field morphology and halo abundance. Our results show that the impact of IDE on quasi-linear and non-linear structure formation cannot be captured by standard $\Lambda$CDM-calibrated prescriptions, highlighting the importance of model-consistent non-linear modelling for future weak-lensing and large-scale-structure constraints on interacting dark energy cosmologies.

      Orateur: Yuejia Zhai (University of Sheffield)
    • 15:20
      coffee break
    • 43
      Quantifying Anisotropies in the Local Expansion Rate with Cosmic-Flows 4

      The Cosmological Principle predicts that, on sufficiently large scales, cosmic expansion should appear statistically isotropic to all observers. Testing the limitations of this prediction in the local Universe is, therefore, a first step into properly considering the impacts of local large-scale anisotropies in data analysis and interpretation. In this work, we use the Cosmicflows-4 distance compilation to reconstruct spatial fluctuations in the local expansion rate (up to $z=0.1$), obtaining its low $\ell$ multipoles, with special focus on the dipole and quadrupole of the expansion. The analysis is done in a completely model-independent way, allowing for a direct test of statistical isotropy without assuming a fiducial cosmological model. While the multipole amplitudes remain broadly consistent with $\Lambda$CDM expectations, the dipole and quadrupole exhibit a persistent coherence in direction across different redshift shells, with a probability below 0.001% in standard cosmological realizations. In this talk I will discuss the details and consequences of such findings.

      Orateur: Jessica Santiago (Aix Marseille University)
    • 44
      The Universal Rotation Curve of disk galaxies: probing dark matter and the local expansion rate

      The Universal Rotation Curve provides a powerful empirical framework to investigate the distribution of luminous and dark matter in disk galaxies. By adopting normalized radial and velocity coordinates, we investigate the emergence of universal kinematic properties across galaxies with different masses and luminosities. The resulting co-added rotation curves will be analyzed through different dark matter mass models to constrain the halo density profiles. Finally, we discuss the use of the radial Tully–Fisher relation to obtain an independent estimate of the local Hubble constant. This work represents a first step toward a unified analysis of galaxy rotation curves and their cosmological applications.

      Orateur: Tiziano Schiavone (SISSA, Trieste)
    • 45
      SH0ES update
      Orateur: Adam Riess
  • mar. 21 juillet
    • 46
      Stress-testing LCDM with large-scale structure

      I will outline the ways in which cosmological observations of large-scale
      structure can test departures from LCDM or, more generally, apparent violations of
      general relativity. These observations include a broad variety of cosmological
      probes that are now being exploited by spectroscopic and photometric
      surveys. I will focus on the basics physics behind these probes, and end with
      the outline of the formalism that compares the geometrical and growth aspects
      of LSS that can provide a very general stress-test of the cosmological model.

      Orateur: Dragan Huterer (University of Michigan)
    • 47
      Combined probes of dark energy

      I will discuss challenges and opportunities for probing dark energy with diverse observational probes, including CMB, galaxy clustering, cosmic shear, and 21cm intensity mapping. I will highlight the role of accurate nonlinear modelling and modern statistical techniques to mitigate various issues in the data analysis. I will present results from re-analysing data from surveys like BOSS, KiDS, and DESI, as well as forecasts for surveys like Euclid and Rubin.

      Orateur: Alkistis Pourtsidou (University of Edinburgh)
    • 10:30
      Coffee break
    • 48
      DESI Full-Shape Constraints and the Challenge of Bias Degeneracies

      The Dark Energy Spectroscopic Instrument (DESI) provides highly precise measurements of galaxy clustering. To extract the maximum cosmological information from these datasets, Full-Shape and ShapeFit analyses based on the Effective Field Theory of Large-Scale Structure (EFTofLSS) have become the standard approach. However, marginalizing over a broad parameter space of EFTofLSS nuisance parameters (galaxy bias, counter- and stochastic terms) introduces significant degeneracies that weaken cosmological constraints.

      In this talk, I will review recent full-shape and ShapeFit results from DESI, focusing on how these nuisance parameter degeneracies impact current cosmological inference. Finally, I will discuss theoretical avenues aimed at mitigating these limitations. I will outline an approach to higher-order bias featuring environmental dependence, inspired by the web-halo model. By physically conditioning halo formation on the surrounding cosmic web, this framework seeks to provide analytical priors for non-linear biases, offering a potential pathway to break EFTofLSS degeneracies in ongoing and future large-scale structure surveys.

      Orateur: Samuel Brieden (TTK, RWTH Aachen)
    • 49
      Theories of Large-Scale Structure and Newtonian Motion Gauges

      Standard Perturbation Theory, Effective Field Theory and other theories of large-scale structure are usually formulated in terms of Newtonian equations. Newtonian motion gauges were initially designed to enhance Newtonian N-body simulations. They also offer an opportunity to perform SPT or EFTofLSS calculations within a general-relativistic framework. At the same time, they allow to incorporate the effects of radiation, massive neutrinos, and certain classes of non-standard dark matter and modified gravity models "for free", without increasing the computational cost of loop calculations with respect to the pure LambdaCDM limit. We present a proof of concept for the calculation of the one-loop matter power spectrum in real and redshift space in presence of massive neutrinos.

      Orateur: Julien Lesgourgues (RWTH Aachen University)
    • 12:30
      Lunch Break
    • 50
      BAO Experiments in Tension: Methods, Redshift Coverage, and Interpretation

      I will talk about systematic differences between 2D and 3D Baryon Acoustic Oscillation (BAO) analyses. While 2D BAO measurements appear to ease the Hubble tension by accommodating both a higher H₀ and a larger sound horizon, they simultaneously introduce tension with Planck constraints on Ωₘh², reflecting systematic shifts relative to 3D analyses.

      I then examine the apparent preference for dynamical dark energy in DESI DR2 when combined with Planck, and contrast it with SDSS BAO results. DESI probes a lowest mean redshift of z = 0.295, whereas SDSS reaches z = 0.11. Because w₀ and q₀ describe present-day cosmic expansion, access to lower-redshift data is decisive: SDSS constrains these parameters largely in a data-driven manner, while DESI’s higher minimum redshift makes them more dependent on model extrapolation. Adding low-redshift supernova data restores consistency with ΛCDM. I therefore argue that the apparent DESI preference for dynamical dark energy may reflect redshift sampling rather than new physics, and suggest that finer tomographic binning of the DESI Bright Galaxy Survey (BGS) to reach lower effective redshifts will be crucial to test this conclusion.

      Orateur: Ruchika Ruchika (University of Salamanca)
    • 51
      Beyond ΛCDM with a Logistic RG-like Flow of the Low Redshift Cosmic Evolution

      Recent observations hint at possible late-time deviations from ΛCDM. We introduce a minimal phenomenological framework in which the total equation of state wT(z) follows a logistic evolution motivated by renormalization-group–like flow between cosmological fixed points. Using DESI-DR2 BAO, DES supernova data, and CMB distance priors, we find that this parametrization provides an improved description of the expansion history relative to ΛCDM. The reconstructed evolution, though model specific, also shows statistically strong low-redshift deviations from ΛCDM.

      Orateur: Prof. Anjan Ananda Sen (Jamia Millis Islamia)
    • 52
      Mimicking Phantom Dark Energy with Evolving Dark Matter Mass

      I will present a framework to reproduce any cosmological background via energy exchange between dark energy and dark matter, where a quintessence field controls the DM mass. This setup achieves a phantom-crossing background without introducing ghosts. As a proof of concept, I will reproduce the background that best fits the recent DESI+CMB+DESY5 data. While the background expansion is identical, the perturbations differ, altering late-time structure growth while preserving early-universe predictions. I will discuss the resulting $\mathcal{O}(10\%)$ signatures in the matter power spectrum, CMB lensing, and the ISW effect, which provide clear, testable signatures for future surveys.

      Orateur: ALESSIO NOTARI (Universita di Roma Sapienza)
    • 53
      Defocusing dark energy: Raychaudhuri diagnostics beyond $w<-1/3$ and the phantom divide

      Evolving dark energy is back at the center of cosmology, and several scenarios under active discussion---sign-switching $\Lambda_{\rm s}$CDM, AdS-to-dS transitions, and modified-gravity backgrounds recast in GR like form---feature an effective dark-energy density that is negative in the past and crosses zero at some redshift $z_\dagger$. Our standard language quietly assumes this never happens: $w_{\rm de}<-1/3$ signals repulsion only while $\rho_{\rm de}>0$, the phantom divide $w_{\rm de}=-1$ stops separating anything once the density changes sign, and at $\rho_{\rm de}=0$ the ratio $w_{\rm de}$ does not exist at all, even though nothing physical is singular there. In this talk we ask what defines dark energy when $w$ cannot, and answer with the two combinations the field equations actually use: the active gravitational mass density $\mathcal{M}=\rho+3p$, which drives Raychaudhuri defocusing, and the inertial mass density $\mathcal{I}=\rho+p$, whose zero is the null-energy-condition boundary. Three clean results follow: any smooth sign switch is necessarily phantom-like and repulsive at the crossing; the accompanying pole in $w_{\rm de}$ is purely kinematic, with a universal residue fixed only by $z_\dagger$ and the order of the zero; and repulsion begins strictly before the switch, at a distinct redshift $z_{\rm rep}>z_\dagger$, with sufficiently sharp transitions opening a transient acceleration window at intermediate redshift. We illustrate these results with an analytic profile, $f(T)$ gravity, and the minimal phantom brane, and close with the practical moral for reconstructions: across $\rho_{\rm de}=0$, the regular targets are $(\mathcal{I},\mathcal{M})$, not $w_{\rm de}$.

      Orateur: Prof. Özgür Akarsu (Istanbul Technical University)
    • 54
      Reframing the Hubble Tension Through the Sound Horizon

      One of the most striking open problems in modern cosmology is the Hubble tension: the persistent disagreement between measurements of the present-day expansion rate of the Universe obtained from local observations and the lower values inferred from cosmic microwave background data within the standard ΛCDM framework. This mismatch has motivated extensive scrutiny of both late-time measurements and early-Universe assumptions.
      Furthermore, this discrepancy may point to gaps in our understanding of the physics around the epoch of recombination, where the sound horizon at decoupling plays a central role. Because the value of the sound horizon depends on the microphysics of the early Universe, it is crucial to derive both H0​ and the sound horizon without relying on model-dependent assumptions. In this talk, I will present recent work demonstrating how the combination of baryon acoustic oscillations with CMB lensing and galaxy weak lensing and clustering enables sound-horizon–agnostic determinations of the Hubble constant, and I will discuss how allowing for massive neutrinos impacts the inferred value of H0​.

      Orateur: Helena García Escudero (Univesity of Southern California)
    • 15:40
      Coffee Break
    • 55
      Constraining 2-loop EFTofLSS with weak lensing

      We present the Sym-EFT emulator [arXiv:2511.05093], which enables fast and accurate predictions for the nonlinear matter power spectrum up to two loops within the Effective Field Theory of Large-Scale Structure (EFTofLSS). We discuss its applications to weak gravitational lensing, including constraints on 2-loop EFTofLSS counterterms from current DES Year 3 cosmic shear and CMB lensing data. We study the sensitivity of these lensing observables to EFT contributions and assess their constraining power on effective parameters describing nonlinear clustering. Our results demonstrate the potential of combining EFT-based modelling with current weak lensing measurements for precision cosmology.

      Orateur: DESPOINA FARAKOU (CEICO, FZU)
    • 56
      EFT-Ramses Effective Field Theory of Dark Energy

      While the standard Lambda-CDM model has been an excellent empirical fit since the discovery of cosmic acceleration, theoretical challenges surrounding the cosmological constant (Lambda) have strongly motivated the exploration of alternative MG and dynamical DE frameworks. Investigating the physical nature of this acceleration requires N-body simulations, preparing for the high-precision data from upcoming Stage-IV surveys, it is strictly required to probe the non-linear growth of cosmic structure. In this paper, we present EFTRAMSES, a comprehensive extension of the ECOSMOG N-body simulation code designed to explore non-linear structure formation in these MG and DE scenarios. We embed the EFTofDE framework into our computational pipeline, utilising the alpha-basis parameterisation to demonstrate the code's capability to directly simulate the EFT framework itself. To validate this new architecture, we additionally map and simulate structure formation within the GCCG model, comparing the resulting non-linear matter power spectra against independent, established baseline code. Our results demonstrate excellent code-to-code agreement, achieving sub-percent precision on linear and quasi-linear scales (k ≤ 1 h/Mpc) and remaining strictly bounded within a 1-2% margin deep into the non-linear regime across multiple cosmic epochs. Crucially, EFTRAMSES successfully captures the highly non-linear Vainshtein screening mechanisms accurately reproducing the ~7% peak enhancement in structure formation at quasi-linear scales before dynamically suppressing the fifth force in high density environments. By consolidating diverse scalar-tensor theories into a single "master" Vainshtein equation, this pipeline provides a robust and versatile computational tool for generating the precise non-linear predictions required for upcoming cosmological surveys.

      Orateur: Nathaniel Woodcock (Durham University)
    • 57
      Dynamical dark energy from QCD vacuum

      The nature of dark energy has been a growing point of debate in recent years, particularly after the DESI measurements of the Baryon Acoustic Oscillations. While frequentist metrics appear to indicate a growing preference for a dynamical dark energy, some bayesian approaches indicate otherwise. Beyond this, there also lies the question of whether there exists a physical motivation behind any phenomenological parametrisation of dynamical dark energy.
      The model described in this talk is motivated from computations of the non-perturbative QCD vacuum, which we parametrise into a dynamic, non-local contribution to the energy density, described by two additional cosmological parameters. I will describe how this model compares against both CPL and ΛCDM on the latest cosmological datasets, in both χ² statistics and Bayesian model comparison.

      Orateur: Dong Ha Lee (University of Sheffield)
    • 58
      Deciphering the coupled scalar dark sector.

      The dark sector represents the elusive nature of dark matter and dark energy. Possible sources of the dark sector have long been studied, and with recent data releases from the Dark Energy Spectroscopic Instrument (DESI), interest in scalar field sources for the dark sector has been revived. This talk presents recent work examining scalar fields sourcing the dark sector, with a focus on the effects of couplings in the kinetic and potential terms of the scalar fields’ Lagrangian. I will elaborate on the framework of dynamical systems that we use to analyse the effects of said couplings applied to two cases of interest involving coupled dark matter and dark energy scalar fields, as well as the case of a multi-field sourced dark energy. I will also discuss the approach taken to examine the effects of the couplings at linear order and future prospects for the coupled scalar dark sector and implications of data signatures.

      Orateur: Saba Rahimy (Swansea University)
  • mer. 22 juillet
    • 59
      Cosmology probes of Dark Matter

      In this talk, I will present a review of selected cosmological probes of dark matter, considering both particle candidates and macroscopic objects such as primordial black holes. These probes may test energy injection or the damping of small-scale structures in the early Universe. Whenever possible, I will highlight how these probes and their associated methodologies can be used to tighten constraints on the viable parameter space of other exotic components, such as primordial magnetic fields.

      Orateur: Laura Lopez Honorez (Université Libre de Bruxelles)
    • 60
      Constraints on the Injection of Radiation in the Early Universe

      We consider the generic injection of radiation (both dark and electromagnetic) during the epoch between big bang nucleosynthesis (BBN) and recombination. The contribution of the additional radiation to the number of effective neutrinos may be quite small in this scenario, since dark radiation and electromagnetic radiation provide contributions of opposite sign. However, the injection of electromagnetic radiation dilutes the baryon-to-entropy ratio, which is measured both at BBN and at recombination. As a result, this scenario is expected to be tightly constrained. Indeed, performing a numerical study, we find that the allowed amount of extra radiation may be no more than $\sim 25\%$ greater than in the case where it is assumed to be entirely dark radiation.

      Orateur: Jason Kumar (University of Hawaii)
    • 10:30
      Coffee break
    • 61
      Unifying Early and Late Dark Energy

      Unifying Early and Late Dark Energy

      Orateur: Jeremy Sakstein (University of Hawai'i)
    • 62
      Waving in the Dark: Noisy, Warm, and Spinning Dark Fields

      When bosonic dark matter is sufficiently light, wave-dynamical effects can manifest on astrophysical and even cosmological scales. I will review a range of such phenomena across both linear and nonlinear regimes, including enhancements and suppressions in the density power spectrum, wave interference, soliton formation, and in some cases, generation of macroscopic spin angular momentum density. I will then discuss observational avenues to detect or constrain these effects, and how they can shed light on the the fundamentail properties of these dark fields (number, mass, spin etc), and their cosmological production mechanisms.

      Orateur: Mustafa Amin (Rice University)
    • 12:30
      Lunch break
    • 63
      Exploring the Lyman-Alpha Forest in a Dynamical Dark Energy Cosmology using Cholla

      The Dark Energy Spectroscopic Instrument (DESI) Collaboration, when combining their baryonic acoustic oscillation observations with measurements of supernova surveys and cosmic microwave background data, inference of a best fit cosmology with a time-varying dark energy motivates independent observational tests of a departure from a cosmological constant dark energy. I will discuss the results of a limited set of hydrodynamic cosmological simulations on how a dynamical dark energy component may imprint itself on the Lyman Alpha forest of neutral hydrogen absorption. In comparing a dynamical dark energy cosmology of the kind inferred by the DESI Collaboration to one evolved with a cosmological constant, we find a redshift-dependent spectral tilt in the transmitted flux power spectrum. These dynamical dark energy models exhibit a slightly warmer intergalactic medium and a lower Lyman Alpha optical depth.

      Orateur: Diego Garza (University of California, Santa Cruz)
    • 64
      Unveiling the Dark Universe with the Sun

      The sun is a powerful tool for investigating the dark universe. In the core of the sun light scalar particles can be produced via Primakoff process in the electric field of the ions and via the intense magnetic field. There can also be production vis the magnetic field in the tachocline. This allows for stringent constraints on new scalar particles which could play the role of dark energy. This will be discussed

      Orateur: Prof. Anne Davis (University of Cambridge)
    • 65
      Time-domain axion searches with magnetic white dwarfs

      Magnetic white dwarfs can convert photons into axions in their strong magnetic fields, with the conversion probability modulating the light curve as the star rotates. However, this observable is degenerate with intrinsic stellar variability if the background is modeled too simplistically. We develop a controlled background-degeneracy framework that computes the axion-induced modulation from reconstructed stellar magnetic fields while fitting it simultaneously with a flexible Fourier model of the intrinsic light curve. Applying this framework to TESS observations of PG 1015+014 using two independent magnetic field reconstructions, we find that a sinusoidal stellar background can produce an apparent preference for nonzero axion-photon conversion. This preference is absorbed once the background light curve includes the second harmonic, indicating that higher-harmonic stellar variability is a leading degeneracy for precise photometric axion searches in magnetic white dwarfs. Interpreting the two-harmonic fit as a conservative baseline, we obtain stringent constraints on the axion-photon coupling for sub-μeV axions. We further derive an analytic target-ranking estimate for other TESS magnetic white dwarfs, identifying systems where phase-resolved magnetic modeling would be most valuable for competitive axion probes.

      Orateur: Hong-Yi Zhang
    • 66
      Halo Abundance in Decaying Dark Matter Models

      Decaying dark matter (DDM) provides a well-motivated extension of $\Lambda$CDM, in which two-body decays – characterized by a decay rate $\Gamma$ and velocity kick $v_k$ – naturally suppress structure growth and lead to lower clustering amplitudes consistent with weak lensing measurements of $S_8$. Previous analyses combining Planck, BAO, and weak lensing data identified viable parameter space around $\Gamma^{-1}\sim7~$Gyr and $1250~$km/s. Extending these constraints with upcoming cluster abundance measurements from eROSITA, however, requires accurate theoretical predictions for the halo mass function in DDM cosmologies.
      We show that the standard Press–Schechter formalism, even when supplied with the correct DDM linear power spectrum, systematically overpredicts the abundance of massive halos compared to DDM N-body simulations. This discrepancy arises from neglecting the distinct collapse physics of DDM, including the exponential decay of parent particles and mass loss from halos due to daughter particles receiving velocity kicks that exceed the escape velocity. We develop a spherical collapse framework that self-consistently incorporates these effects, yielding a mass-dependent critical density threshold $\delta_c(M)$ that increases for low-mass halos unable to retain kicked daughters. This leads to a suppression of low-mass halo abundances while recovering $\Lambda$CDM behavior at high masses. Comparing our theoretical predictions to simulations, we find that the DDM parameter space favored by Planck and weak lensing data produces substantially modified halo mass functions, indicating that eROSITA cluster counts should place significantly stronger constraints on decaying dark matter models.

      Orateur: Thomas Montandon (Laboratoire Univers et Particule de Montpellier (LUPM))
    • 67
      Asymmetric Reheating of Dark QED

      The reheating epoch following inflation sets the initial conditions for the subsequent thermal history of the Universe, but remains largely unconstrained prior to Big Bang nucleosynthesis. In many extensions of the Standard Model, the inflaton may decay simultaneously into visible and hidden sectors, leading to non-standard cosmological histories. One possibility is an asymmetric reheating in which unequal amounts of energy are deposited in the visible and dark sectors, resulting in different temperatures and potential entropy exchange between them. In this talk, I will study asymmetric reheating in a simple and instructive hidden sector framework: dark QED, consisting of a Dirac fermion dark matter candidate charged under a dark U(1)′ gauge symmetry and a massive dark photon coupled to the visible sector via kinetic mixing. I will focus on the thermalization of dark QED after inflation, during reheating, in the weak-coupling and initially under-occupied regime. I will then discuss the evolution of the temperature ratio during the reheating process. I will finally describe the implications for thermal dark matter production, highlighting viable regions of parameter space where dark matter is thermalized at a temperature different from that of the Standard Model.

      Orateur: Simon Clery (Technical University of Munich (TUM))
    • 15:40
      Coffee Break
    • 68
      Large deviations for halos and voids: beyond perturbative non-gaussianities

      The excursion-set formalism provides a key connection between primordial inflationary fluctuations and the abundance of cosmic structures such as dark matter halos and voids, traditionally assuming Gaussian random walks. In this work, we extend this framework to fluctuations whose distribution presents strongly non-Gaussian tails, beyond the reach of perturbative approaches to primordial non-Gaussianity based on moment expansion. We address the problem with rigorous, analytical derivations relying on the large deviation principle, suited for the study of rare fluctuations. We derive new first-passage time distributions for random walks with non-Gaussian statistics and obtain updated predictions for the halo mass function. We also study the two-barrier first-passage problem relevant to cosmic void formation, leading to a new analytical prediction for the void size function, with improved accuracy on large scales. Our results demonstrate the potential of large deviation techniques as a bridge between inflationary scenarios, often leading to strongly non-Gaussian tails, and late-Universe observables.

      Orateur: Martin Teuscher (LPSC Grenoble, France)
    • 69
      A superposition quantum universe and its perturbations

      In the quest to establish possible imprints of quantum gravity we consider so-called minisuperspace models that should be understood as a low energy limit of a full quantum gravitational theory. Starting from a bouncing minisuperspace model that resolves the big bang singularity, we will relax the assumption that the state of the quantum universe has to correspond to a single highly semiclassical state. Instead, we will consider a universe in a superposition of such states.
      Faced with the question of how to extract a semiclassical scale factor that can be connected to the classical evolution of general relativity, we propose to make use of the trajectory approach to quantum mechanics. We illustrate the treatment of cosmological perturbations over a superposition background described by a trajectory and consider implications for the resulting power spectrum. Notably these spectra can exhibit features that significantly differ from the single state case.

      Orateur: Lisa Mickel (Institut d'Astrophysique de Paris)
    • 70
      Beyond LCDM: Dynamical Dark Energy and High-Redshift Reionization

      This talk will explore deviations from the standard cosmological model across cosmic history. First, I will present data analysis results on dynamical dark energy using a novel pressure parametrization and four parameters parametrization testing by the latest datasets. Second, I will discuss model-independent reconstructions of the reionization history using Gaussian processes. We utilize these reconstructions to place robust bounds on exotic energy injections and decaying particle models.

      Orateur: Hanyu Cheng
    • 71
      Isocurvature Induced Gravitational Waves at Pulsar Timing Arrays

      The standard cosmological model (ΛCDM model) assumes adiabatic initial conditions for primordial density perturbations. However, many new physics scenarios can deviate from this assumption and generate isocurvature perturbations across a wide range of scales. In this talk, I will discuss how isocurvature can induce gravitational waves at second order in perturbation theory. Moreover, Pulsar Timing Arrays can set stringent limits on isocurvature around $10^6\,\textrm{Mpc}^{-1}$ via isocurvature-induced gravitational waves.

      Orateur: Peizhi Du (University of Science and Technology of China)
  • jeu. 23 juillet
    • 72
      Time-delay cosmography: present and future

      Strong gravitational lenses with measured time delays between the multiple lensed images provide an effective way to measure the Hubble constant H0, a key cosmological parameter that sets the expansion rate of the Universe. Lensed quasars with exquisite observations have been used to measure H0, providing competitive results. Exciting discoveries of the first strongly lensed supernovae are starting to yield H0 measurements. In this presentation, I will provide an overview of recent H0 measurements from both lensed quasars and lensed supernovae. I will show the bright prospects of lensed transients as an independent and competitive cosmological probe.

      Orateur: Sherry Suyu (Technical University of Munich / Max Planck Institute for Astrophysics)
    • 73
      Standard siren cosmology

      Thanks to the synergies between gravitational wave (GW) experiments, such as LIGO/Virgo/KAGRA, and electromagnetic observations of transients and galaxies, a variety of novel cosmological measurements has recently become possible. Several of these measurements rely on the use of GW events as "standard sirens”. Following the detection of the first electromagnetic counterpart to a GW event, GW170817, the first “bright” standard siren measurement has been performed. We continue searching for optical counterparts to enable more bright siren analyses, while standard siren measurements for “dark" events, i.e. without a confirmed electromagnetic counterpart, can also be performed. In this talk I will show some of the latest standard siren measurements, and present expectations for multi-messenger detections in the upcoming years.

      Orateur: Antonella Palmese (Carnegie Mellon University)
    • 10:30
      Coffee break
    • 74
      Shedding light on the Hubble tension with novel cosmological probes: Cosmic Chronometers and Gravitational Waves

      Modern cosmology is entering a critical phase, as increasingly precise measurements from multiple standard probes have unveiled tensions that may hint at new physics. Whether these discrepancies arise from unaccounted systematics or signal a genuine crisis in our understanding of the Universe is still an open question. In this context, it becomes crucial to explore independent and complementary approaches to constrain cosmology.

      In this talk, I will present two independent and novel ways to tackle the expansion history of the Universe without relying on distance ladder calibration, cosmic Chronometers (CC) and Gravitational Wave standard sirens (GW).
      Cosmic Chronometers exploit the differential age evolution of passively evolving galaxies to directly measure the Hubble parameter H(z), providing a fully cosmology-independent reconstruction of the expansion history. Gravitational Wave standard sirens, on the other hand, offer an absolute measurement of luminosity distances through the direct observation of compact binary mergers, independently anchoring the cosmic distance scale.
      I will discuss the current status of both methods, their individual strengths and limitations, and, crucially, their synergy: used in combination, CC and GW probe complementary aspects of cosmic expansion and offer a joint pathway to address the Hubble tension with minimal theoretical assumptions. Finally, I will explore how ongoing and upcoming surveys and observatories (such as Euclid, WST, and next-generation GW detectors like Einstein Telescope and LISA) will dramatically improve the constraining power of both probes, paving the way toward their full inclusion in the era of precision cosmology.

      Orateur: Michele Moresco (University of Bologna)
    • 75
      Evidence of evolving dark energy from a Hubble Diagram of Quasars

      I present new cosmological fits to the Hubble diagram built from supernovae and a homogeneous quasar sample spanning a redshift interval z = 0.7--3.5. The quasar distances are derived from the non-linear relation between X-ray and UV luminosities, and the sample is selected to minimize dust reddening, gas obscuration, host-galaxy contamination, and selection biases. This provides high-quality constraints in a redshift range otherwise poorly covered by Type~Ia supernovae. The main results are: (1) the combined Hubble diagram shows strong (> 4 σ) tension with the standard flat ΛCDM model at z ≥ 1.5; (2) in the overlap region, the quasar and supernova Hubble diagrams are fully consistent, supporting a common distance scale; (3) allowing for an evolving dark-energy equation of state yields a significantly better fit, with w_0 and w_a values compatible with those favored by recent DESI results; (4) our quasar Hubble diagram and cosmological constraints agree closely with an independent analysis based on ~6,000 quasars standardized via variability distances (Dutra et al.~2026). The convergence of two independent quasar methods strengthens the case that the deviation from flat \lcdm at high redshift is not driven by sample-specific systematics.

      Orateur: Guido Risaliti (Università di Firenze)
    • 12:30
      Lunch break
    • 76
      cloe-org: a new computational environment for LSS cosmology

      The latest generation of large-scale structure surveys requires computational frameworks that are not only accurate, but also modular, reproducible, fast and sustainable in time. We present cloe-org, a new computational environment for LSS cosmology, built around the development of CLOE: the Cosmology Likelihood for Observables in Euclid. Designed to support end-to-end cosmological analyses, cloe-org brings together theoretical modelling, likelihood evaluation, inference tools, validation workflows, and collaborative software practices within a unified ecosystem. Its current applications span spectroscopic galaxy cluster, and weak lensing, photometric clustering, galaxy-galaxy lensing, and their combinations, while allowing for the inclusion of key astrophysical and observational systematics and some cross-correlation with CMB. By providing a flexible environment for testing modelling choices, priors, scale cuts, and extended cosmological scenarios, cloe-org aims to make precision LSS analyses more transparent, efficient, and robust. This framework is developed with Euclid in mind, but with the broader goal of serving the cosmology community in the era of high-dimensional, survey-scale inference.

      Orateur: Guadalupe Cañas-Herrera (Leiden Observatory)
    • 77
      Measuring the evolution of the Weyl potential

      The Weyl potential, which is the sum of the spatial and temporal distortions of the Universe's geometry, provides a direct way of testing the theory of gravity and the validity of LCDM. In this talk I will first present a methodology to directly measure the evolution of this potential from galaxy-galaxy lensing measurements with a minimum amount of assumptions. I will then show the results using the Year 3 data from the Dark Energy Survey, and also how these measurements change once we include data from the Dark Energy Spectroscopic Instrument.

      Orateur: Isaac Tutusaus (ICE/IEEC/IRAP)
    • 78
      Constraining structure growth and primordial non-Gaussianity with Euclid AGNs and CMB lensing

      Measuring the growth of cosmic structure across time is a powerful way to test the standard cosmological model. With the Euclid mission, we are gaining an unprecedentedly large and deep sample of Active Galactic Nuclei (AGN), providing a unique, highly biased tracer of large-scale structure reaching far into the high-redshift universe. In this work, we explore the cosmological potential of cross-correlating the spatial distribution of Euclid AGNs with Cosmic Microwave Background (CMB) lensing ($\kappa$) maps from different surveys (Planck, ACT, SO).
      We first outline our forecasting framework based on the mock catalog from Euclid Preparation: XLIX (Bisigello et al., 2024), which presents a pure sample of millions of unobscured AGNs up to $z=5$. By modelling the $\kappa \times \text{AGN}$ cross-correlation, in combination with the auto-correlations $\kappa \times \kappa$ and $\text{AGN} \times \text{AGN}$, we forecast the constraining power of this joint analysis on the redshift evolution of structure growth $\sigma_8(z)$, linear AGN bias, and primordial non-Gaussianity $f_{\text{NL}}$ through the scale-dependent bias effect.
      Following the measurement pipelines established in this theoretical work, the methodology is currently being adapted to the newly acquired Euclid Q1 data. We will discuss our ongoing progress and share early insights from this first look at real observations, outlining our steps toward measuring the clustering properties of the very first Euclid AGN sample.

      Orateur: Matteo Peronaci
    • 79
      KiDS-Legacy: Constraints on Horndeski gravity

      In this talk, I will present constraints on modified gravity using the latest weak lensing data from the Kilo-Degree Survey (KiDS-Legacy), in combination with DESI measurements of baryon acoustic oscillations, eBOSS observations of redshift space distortions, and cosmic microwave background anisotropies from Planck. This analysis explores the Horndeski class of modified gravity models within an effective field theory framework that satisfies stability conditions by construction. We find that cosmic shear provides significant constraints on the Horndeski parameter space, matching or surpassing the CMB contribution, and thus highlighting the role of weak lensing as a powerful probe of gravity on cosmological scales. The results show that although modified gravity provides a slightly improved fit to the data, a model comparison indicates only a weak preference over $\Lambda$CDM, while key observables, such as the structure growth parameter S_8, remain consistent with $\Lambda$CDM constraints.

      Orateur: Dr Benjamin Stölzner (Ruhr University Bochum)
    • 80
      Reconstructing Inflationary Dynamics Beyond Slow Roll from Cosmological Observables

      Understanding the physics of the early Universe remains one of the central goals of modern cosmology. While the inflationary paradigm provides a compelling mechanism for generating primordial perturbations, most observational constraints to date rely on the slow-roll approximation and specific model assumptions. In this talk, I present a model-agnostic approach to probing inflationary dynamics beyond the slow-roll regime, leveraging the latest observations from the cosmic microwave background (CMB) and large-scale structure (LSS).

      By relaxing standard assumptions and allowing for more general departures from canonical evolution, we explore a broader class of inflationary scenarios and their imprints on cosmological observables. This framework enables a systematic search for signatures of non-trivial dynamics in the primordial Universe, including features that may be inaccessible within conventional parametrizations.

      Combining multiple cosmological probes, we demonstrate how current data can be used to place robust, assumption-light constraints on the inflationary epoch. These results open new avenues for testing the fundamental physics driving cosmic inflation and highlight the growing synergy between early- and late-time observables in precision cosmology.

      Orateur: Dr Rodrigo Calderon (Institute of Physics, Czech Academy of Sciences)
    • 15:40
      Coffee Break
    • 81
      Cosmology with the line-of-sight shear of strong gravitational lenses

      Weak gravitational lensing distorts shapes and brightnesses, introducing correlations in the apparent ellipticities of galaxies, and enabling constraints on cosmological parameters such as Omega_m and sigma_8. Strong gravitational lenses are also subject to weak lensing perturbations, leaving a measurable imprint in the form of line-of-sight (LOS) shear. Stage-IV photometric galaxy surveys are on track to detect more than 100 000 strong gravitational lenses, and these could be used as a novel cosmological observable via the correlations between the LOS shear and itself, galaxy positions and galaxy shapes.

      In this talk, I will present the current status of this project, detailing how the LOS shear manifests in strong lensing images, the new correlation functions defined by this observable, and the sources of uncertainty affecting the detectability of these correlations. Considering various scenarios for the stage-IV strong-lensing samples, I will show that the correlation signal will be detectable with a high signal-to-noise ratio even in a pessimistic scenario, and carries great promise for adding statistical power and mitigating systematics in standard 3x2pt analysis.

      Orateur: M. Daniel Johnson (Laboratoire Univers et Particules de Montpellier)
    • 82
      LOS Shear Cosmology - Testing Measurability with Hydrosimulated Strong Gravitational Lenses

      Strong gravitational lensing is an increasingly powerful tool for cosmological studies. In particular, the weak-lensing shear induced by large-scale structures along the line of sight (LOS) of a strong lens can itself be treated as an observable, carrying information about the matter distribution in the Universe and thus representing a valuable cosmological probe.

      While the theoretical feasibility of this approach has been demonstrated, its practical observability and the precision achievable in realistic settings remain largely unexplored.

      In this work, I investigate these questions using simulated lenses. Rather than relying solely on analytical mass models, I developed a pipeline to extract lens galaxies from state-of-the-art hydrodynamical simulations and generate mock lensed images, which are then analysed with current lens-modelling techniques. This allows us to assess the impact of realistic mass distributions and modelling assumptions on the recovery of the LOS shear signal.

      I will present the first results of this simulation and modelling effort, and discuss the caveats and limitations of this approach.

      Orateur: Giacomo Queirolo
    • 83
      Constraints on cosmology with transverse-velocity and CMB cross-correlations

      On large scales, peculiar velocities encode a wealth of cosmological information. While line-of-sight components are routinely probed, measuring transverse velocities has remained challenging. I will present a new detection of dipolar patterns associated with transverse velocities, imprinted on the Cosmic Microwave Background through the integrated Sachs–Wolfe effect and gravitational lensing. These new measurements provide new constraints on general relativity.

      Orateur: Yanchuan Cai (University of Edinburgh)
    • 84
      Breaking Galaxy–Halo Degeneracies with Anisotropic Small-Scale Three-Point Clustering

      Small-scale galaxy clustering contains cosmological information that is complementary to standard BAO measurements and potentially highly constraining for tests of structure growth and fundamental physics. Realizing this potential, however, requires a robust treatment of the uncertain connection between galaxies and dark-matter halos. In this talk, I will present two recent studies that quantify both the opportunity and the challenge.

      First, using LRG-like mock catalogs from the AbacusSummit suite spanning 81 cosmologies, we assess how strongly small-scale two-point clustering constrains cosmology under different assumptions about the galaxy–halo connection. We find a wide gap between an optimistic case in which halo occupation parameters are known and a conservative case in which they are broadly marginalized over. This result shows that small-scale clustering alone can be strongly limited by galaxy-halo degeneracies, and that informative physical or empirical priors are essential for extracting its full cosmological power.

      Second, I will present forecasts for a compressed, line-of-sight-dependent three-point correlation function measured on scales below 80 Mpc. Using Roman-like ELG and DESI-like LRG mocks, we find that adding this statistic to two-point clustering substantially improves constraints on sigma_8 after marginalizing over halo occupation uncertainty. The gain is distributed across many triangle configurations and is significantly larger when line-of-sight information is retained than when only the three-point monopole is used.

      Together, these results motivate higher-order, anisotropic small-scale clustering as a promising route toward more robust cosmological inference from forthcoming Roman, DESI, and related galaxy surveys.

      Orateur: Lado Samushia (Kansas State University)
  • ven. 24 juillet
    • 85
      Recent progress on cosmic inflation

      I will review recent progress on inflation with particular attention to axion-inflation models, their dynamics and gravitational wave/PBH signatures.

      Orateur: Dr Matteo Fasiello (IFT Madrid)
    • 86
      Cosmological implications of generic features of string compactifications

      I will review the cosmological implications of generic features of string compactifications like the presence of fundamental strings, field-dependent couplings, rolling moduli which are gravitationally coupled, axion-like particles and hidden photons. These implications include inflation, cosmic superstrings and gravity waves, reheating, dark radiation and dark energy.

      Orateur: Michele Cicoli (University of Bologna)
    • 10:30
      Coffee break
    • 87
      Gravitational waves from Inflation

      Primordial gravitational waves offer a rare opportunity to probe physics at extremely high energies, opening a window onto the very earliest moments of the universe's history. I will discuss how cosmic inflation can lead to new and distinctive gravitational-wave signals within the reach of current and/or near-future interferometers. I will also show how anisotropies in the gravitational-wave background can become a powerful new way to probe the inflationary era, helping us tell apart inflationary signals from those produced by other cosmic or astrophysical sources.

      Orateur: Ema Dimastrogiovanni (VSI Institute, University of Groningen)
    • 88
      The H0 world cup

      With the Hubble tension recently reaching a level of around $7\sigma$ and supported from various independent directions, now it is more crucial than ever to compare the performance of different mechanisms to ease the Hubble tension. In this talk I present a fair comparison of such models dubbed the $H_0$ world cup, which serves a follow-up to the previous $H_0$ olympics. Improvements include using updated data, new models, and a more comprehensive range of Frequentist and Bayesian metrics. Beyond this baseline comparison, the $H_0$ world cup also includes curvature and CPL dark energy analyses, weighing in also on the preference for thawing dark energy with DESI BAO data in models beyond $\Lambda$CDM. In the knockout round, we investigate also if BBN or $S_8$ can impact the conclusions we draw from the comptetion.

      Orateur: Nils Schöneberg (LMU Munich)
    • 12:30
      Lunch break and end of the conference
  • lun. 27 juillet
    • Registration
    • 89
      Constraints on neutrino masses in light of cosmological tensions

      Cosmological upper bounds on the summed neutrino mass are in increasing tension with respect to laboratory lower bounds as long as standard neutrino physics and the LambdaCDM cosmological model are assumed. I will stress that the tension is driven by measurements of the Universe expansion rate (from BAO, CMB and supernovae data), completed by information from CMB lensing. I will show that there is a variety of physical assumptions allowing to reconcile neutrino mass bounds. I will highlight four very different scenarios doing so.

      Orateur: Julien Lesgourgues (RWTH Aachen University)
    • 10:45
      Coffee Break
    • 90
      How to ease the Hubble tension

      Reducing the sound horizon has been shown to be a very efficient way to reconcile the Hubble tension. In this talk I focus on how and why an increased Hubble parameter can follow from such a reduced sound horizon, and what guardrails the CMB provides in this case. The resulting degeneracies with the other cosmological parameters force models like early dark energy and models that shift the recombination redshift in very different phenomenological directions. Focusing on the latter, I show what kind of interesting phenomenological impacts such models can have while also highlighting the theoretical issues such models still face.

      Orateur: Nils Schöneberg (LMU Munich)
    • 12:30
      Lunch
    • 91
      Reconstructing Inflationary Dynamics Beyond Slow Roll from Cosmological Observables

      Understanding the physics of the early Universe remains one of the central goals of modern cosmology. While the inflationary paradigm provides a compelling mechanism for generating primordial perturbations, most observational constraints to date rely on the slow-roll approximation and specific model assumptions. In this talk, I present a model-agnostic approach to probing inflationary dynamics beyond the slow-roll regime, leveraging the latest observations from the cosmic microwave background (CMB) and large-scale structure (LSS).

      By relaxing standard assumptions and allowing for more general departures from canonical evolution, we explore a broader class of inflationary scenarios and their imprints on cosmological observables. This framework enables a systematic search for signatures of non-trivial dynamics in the primordial Universe, including features that may be inaccessible within conventional parametrizations.

      Combining multiple cosmological probes, we demonstrate how current data can be used to place robust, assumption-light constraints on the inflationary epoch. These results open new avenues for testing the fundamental physics driving cosmic inflation and highlight the growing synergy between early- and late-time observables in precision cosmology.

      Orateur: Dr Rodrigo Calderon (Institute of Physics, Czech Academy of Sciences)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • mar. 28 juillet
    • 92
      Modeling Higher-Order Bias via the Cosmic Web: Implications for DESI Full Shape Analyses

      The standard excursion set approach to dark matter halo formation typically evaluates local collapse without explicitly accounting for the cosmic-web geometry of the large-scale structure. In this talk, I will present a theoretical framework for halo and galaxy bias featuring explicit environmental dependence, inspired by the Web-Halo model. By physically conditioning halo collapse on cosmic web structures—such as sheets and filaments—this framework predicts higher-order and non-linear bias parameters with improved precision.
      I will then explore the observational implications of this theoretical modeling for current large-scale structure surveys, focusing on the Dark Energy Spectroscopic Instrument (DESI). Current DESI full-shape and ShapeFit analyses rely heavily on the Effective Field Theory of Large-Scale Structure (EFTofLSS). A primary bottleneck is the necessity to marginalize over highly degenerate nuisance parameters, which dilutes the final cosmological constraining power. I will discuss how physically motivated, analytical priors derived from environmental bias models can effectively break these EFT degeneracies, offering a robust method to tighten cosmological constraints extracted from the broad-band power spectrum.

      Orateur: Samuel Brieden (ICC, University of Barcelona)
    • 10:45
      Coffee Break
    • 93
      Dark Energy after DESI

      What are the key advances needed in data and in theory to understand dark energy in 2026 and beyond?

      Orateur: Eric Linder (LBL)
    • 12:30
      Lunch
    • 94
      Model Independent Reconstruction of the Cosmological Evolution at Low Redshifts and Possible Theoretical Explanation

      We investigate the late-time expansion history of the Universe using a model-independent reconstruction of
      cosmological distances based on the latest DESI-DR2 BAO measurements and the DES Dovekie Type Ia
      Supernova compilation. We reconstruct the expansion rate over the full redshift range probed by the data and
      compare it with the prediction of the Planck 2018 ΛCDM model. We identify a localized deviation in the
      reconstructed expansion history at intermediate redshifts. We show that this feature persists under variations
      of the reconstruction methodology, dataset composition, sound-horizon calibration, and H0 priors. The
      persistence of the deviation under these tests suggests that it is a robust feature preferred by current low-redshift
      distance measurements and may not be fully explained by modifications affecting only early-Universe physics. We
      subsequently model this deviation using a RG-Flow like Logistic Evolution that gives a statistically better fit than other
      most studied cosmological evolution.

      Orateur: Anjan Ananda Sen (Jamia Millia Islamia Central University)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • mer. 29 juillet
    • 95
      Screened Scalar Fields in Cosmology: Theory and Tests

      Scalar-tensor gravity could help resolve some cosmological mysteries. However such theories give rise to fifth forces, which are not observed in solar system tests of gravity. Hence the coupling between the scalar field and matter must either be very small of the fifth force must be screened. The talk will explain the screen8ng of such scalar fields. It will then look at ways of testing such theories both in the laboratory and with the sun.

      Orateur: Anne-Christine Davis (University of Cambridge)
    • 10:45
      Coffee Break
    • 96
      The influence of small -scale matter fluctuations on the large scale dynamics of light scalars

      Dark matter is present from small to large scales. When dark energy couples to matter, one can integrate out the matter distribution on small enough scales and obtain effects on the dynamics of light scalars (dark energy) on large scales. I will introduce the Schwinger-Keldysh formalism to do this properly and deduce some possible unexpected (?) results for dark energy on large scales.

      Orateur: philippe brax (IPHT Saclay)
    • 12:30
      Lunch
    • 97
      Electromagnetically K-mouflaged dark matter

      I will discuss a cosmological scenario where dark matter is provided with a dark electric charge with a dark electromagnetic sector featuring a screening mechanism so that all the effects only appear at low redshift, when dark matter is sufficiently clustered. Within these models, it is natural to have a universe described by a Lemaitre model instead of a FLRW. Instead of solving the full relativistic equations, I will consider a Newtonian approach that is sufficient for a matter dominated universe with, possibly, a cosmological constant. In this scenario, it is possible to explain the Hubble tension in terms of the dark electric repulsion between dark matter halos. After reviewing some phenomenological consequences, I will proceed to analysing the deformability of dark matter haloes due to the dark electromagnetic interaction and show the emergence of a curious 2-ladder structure connecting different multipoles for the case of Born-Infeld electromagnetism. Furthermore, some multipoles exhibit a vanishing polarisability or magnetisation, thus showing an intriguing resemblance with the vanishing of the Love numbers of black holes. Finally, I will explain how analogous results arise for the scalar DBI theories in arbitrary dimensions and some finite size effects.

      Orateur: Jose Beltrán Jiménez (Universidad de Salamanca)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • jeu. 30 juillet
    • 98
      Interacting dark sectors and axio-dilaton cosmology
      Orateur: Carsten van de Bruck
    • 10:45
      Coffee Break
    • 99
      Lagrangian models of interacting dark matter and dark energy

      Extensions of LCDM with interactions between dark matter and dark energy are a popular route to address the ongoing cosmic tensions. However, many recent models are phenomenological and do not admit a Lagrangian description, leaving their theoretical validity uncertain. One example is phenomenological dark energy fluid models with a phantom equation of state, where the perturbative structure is often ignored; such models are therefore difficult to test for instabilities and pathologies, and harder still to reconcile with fundamental physics. After discussing these challenges, I will introduce several classes of interacting dark sector models derived from Lagrangians. I will cover the two main formalisms for studying relativistic fluids in cosmology: the Brown/Schutz formulations, and the effective field theory approach. I outline the theoretical viability of new and existing models and their distinctive observational signatures. In relation to the S8 tension, I focus on pure-momentum transfer and dark elastic scattering mechanisms. To conclude, I review the current status and future prospects for interacting dark sector models.

      Orateur: Erik Jensko
    • 12:30
      Lunch
    • 100
      Neutrinos, Dark Sectors, and Cosmological Tensions

      While standard LambdaCDM cosmology remains remarkably successful, persistent observational discrepancies suggest the need for physics beyond minimal frameworks. In the talk, we will explore the cosmological implications of deeper, interconnected structures within the dark sector, focusing on new physics interactions between neutrinos, dark matter, and light mediators. We will examine how they could alter early-universe thermodynamics, neutrino free-streaming, and cosmic structure formation. By bridging particle physics models with precision cosmology, coupled dark sectors can naturally impact cosmological tensions while leaving distinct, testable signatures in both next-generation surveys and terrestrial laboratory experiments.

      Orateur: Sebastian Trojanowski (National Centre for Nuclear Research, Poland & Astrocent, NCAC PAS)
    • 15:15
      Coffee Break
    • Discussion: TBD
  • ven. 31 juillet
    • 101
      Quantum Field Theory Approach To Gravitational Wave Physics

      We employ the Quantum Field Theory approach to investigate graviton emission from massive sources. Applying this method to gravitational-wave emission by binary systems in fourth-order gravity, we find a cancellation between the contributions of the massless graviton and the additional massive spin-2 ghost and scalar modes. Consequently, the General Relativity quadrupole formula is not recovered, in conflict with precision measurements of binary systems. Bounds on parameters of the gravitational models under consideration are inferred.

      Orateur: Gaetano Lambiase
    • 10:45
      Coffee Break
    • 102
      Scalar-tensor theories from a particle's perspective

      Scalar–tensor theories provide a theoretically motivated extension of gravity that includes an additional scalar degree of freedom non‑minimally coupled to the gravitational sector. Their consistency with local tests of gravity is possible mainly due to screening mechanisms, which dynamically suppress scalar interactions in high-density environments. In this talk, I will develop a field‑theoretic description of these theories and show that they naturally map to Beyond Standard Model physics. This allows us to place bounds on scalar-tensor theories by using particle phenomenology.

      Orateur: Sergio Sevillano Muñoz (University of Pennsylvania)
    • 12:30
      Lunch
    • 103
      Sign-Switching $\Lambda_{\rm s}$CDM: Theoretical Realizations and Implications for Cosmological Tensions

      The remarkable phenomenological success of the concordance $\Lambda$CDM model is accompanied by persistent tensions and anomalies, including those associated with $H_0$, $S_8$, the growth index $\gamma$, and cosmological inference of the neutrino-mass sum $\sum m_\nu$. These discrepancies may reflect unaccounted-for systematics, but they may also point to missing structure in the standard cosmological framework. In this talk, we discuss $\Lambda_{\rm s}$CDM, a sign-switching effective cosmological-constant scenario in which the dark-energy sector undergoes a rapid, cosmologically late sign transition near $z_\dagger\sim2$, from an AdS-like negative vacuum-energy contribution to a dS-like positive one. Our main focus is the theoretical status of this framework: whether such a transition, either in the abrupt limit or smoothed over a narrow redshift interval, can arise from a more fundamental description rather than being imposed as a phenomenological prescription. We review representative mechanisms and model-building settings capable of generating $\Lambda_{\rm s}$CDM-like dynamics, clarify the physical interpretation of an effective AdS-like--to--dS-like transition in a cosmological background, and discuss its main observational signatures in distance, expansion, and growth probes. For smooth and sufficiently rapid realizations, we also highlight the possibility of a transient intermediate acceleration phase near $z_\dagger$, whose onset can occur on the negative-density branch during the transition epoch. We conclude by commenting on recent observational and theoretical developments, emphasizing how this framework provides a minimal but structurally novel extension of $\Lambda$CDM and a testable route toward addressing cosmological tensions.

      Orateur: Prof. Özgür Akarsu (Istanbul Technical University)
    • 15:15
      Coffee Break
    • Discussion: TBD