Summer school: Les Houches on Dark Universe

Jul 7, 2025, 3:00 PM → Aug 1, 2025, 12:00 PM Europe/Paris

Ecole de Physique des Houches

Guilhem Lavaux (IAP), Pauline Zarrouk (LPNHE), Philippe Brax (Université Paris-Saclay (FR)), Sandrine Codis (CNRS/IAP)

The 2025 summer school focuses on the present and future of cosmology. The program includes lectures on the physics of the late acceleration of the universe's expansion, exploring links with high-energy physics and the relevance of current theoretical models for understanding upcoming data.

Key Topics:

• Tools for analyzing experimental results, including numerical modelling of large-scale structures.
• New probes such as 21 cm physics and the structure of the Dark Ages.
• An overview of dark matter alternatives.

 

Organizing commitee:

• Philippe Brax (IPHT)
• Sandrine Codis (AIM)
• Guilhem Lavaux (IAP)
• Pauline Zarrouk (LPNHE)

 

Scientific organizing committee:

• Francis Bernardeau  (IPHT)
• Alain Blanchard (IRAP)
• Philippe Brax (IPHT)
• Sandrine Codis (AIM)
• Stéphanie Escoffier (CPPM)
• Guilhem Lavaux (IAP)
• Tania Regimbau (LAPP)
• Romain Teyssier (Princeton University)
• Pauline Zarrouk (LPNHE)

_{(Image logo drawn by DALL-E 3)}

Monday, July 7

4:00 PM → 5:30 PM Lecture: The standard model of cosmology: a critique of its status

4:00 PM Long lecture 1

Speaker: Pedro Ferreira

5:30 PM → 6:00 PM Coffee break

6:00 PM → 7:30 PM Lecture: The standard model of cosmology: a critique of its status

6:00 PM Long lecture 2

Speaker: Pedro Ferreira

Tuesday, July 8

9:00 AM → 10:30 AM Lecture: The standard model of cosmology: a critique of its status

9:00 AM Long lecture 3

Speaker: Pedro Ferreira

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Dark energy-vs-high energy physics

11:00 AM Long lecture 1

Speaker: Cliff Burgess

2:00 PM → 3:30 PM Lecture: The standard model of cosmology: a critique of its status

2:00 PM Long lecture 4

Speaker: Pedro Ferreira

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Lecture: Dark energy-vs-high energy physics

4:00 PM Long lecture 2

Speaker: Cliff Burgess

Wednesday, July 9

9:00 AM → 10:30 AM Contributions

9:00 AM Second Order Cosmological Perturbation Theory over the Geodesic Light-Cone Background

Using the Geodesic Light-Cone (GLC) coordinates, one can obtain fully non-linear expressions for light-like cosmological observables. Indeed, by exploiting the intrinsic nature of these coordinates, one can construct an exact, non-perturbative metric that contains all the information about the inhomogeneities and anisotropies present in the observed universe. Meanwhile, it is also interesting to study a perturbation theory on top of the background metric expressed in terms of the GLC coordinates. In this talk, I will tackle this issue at the second perturbative order, going beyond the first order analysis already present in the literature. In particular, I will describe the gauge transformations of second order perturbative functions on the light-cone. Then, after a proper matching with standard perturbation theory, I will find the standard second order gauge fixing corresponding to the GLC gauge. The latter is called the observational synchronous gauge, and I will highlight its conceptual differences with respect to the extension to the second order of the standard synchronous gauge. Finally, within this new perturbation theory, I will evaluate the angular distance-redshift relation up to the second perturbative order as seen by a free-falling observer.

Speaker: Pierre Béchaz (University of Pisa and INFN, Section of Pisa)

9:25 AM Observational constraints of diffusive dark-fluid cosmology

In this manuscript, the background and perturbed cosmic dynamics have been investigated using an interacting dark-fluid model by assuming energy exchange between dark matter and dark energy through a diffusion mechanism. We solve the background expansion history for the late-time Universe and derive the full set of the evolution equations of the matter density contrast, $\delta(z)$ and redshift space distortion, $f\sigma_8(z)$, using the $1+3$-covariant formalism. We then seek to constrain the best-fit cosmological parameters: $h$, $\Omega_m$, $r_d$, $M$, $\sigma_8$, and the interaction term $Q_m$ through the MCMC simulations with cosmological datasets. Using the joint datasets of the Hubble parameter measurements from cosmic chronometers (CC), Baryon Acoustic Oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI), and SNIa distance moduli from Pantheon+ SH0ES, redshift space distortion (RSD) from large-scale galaxy surveys, a detailed statistical analysis of the work is made. To evaluate the dark-fluid model's viability in describing late-time cosmic dynamics, the numerical results of background cosmological parameters are presented. The results show that the dark-fluid behaves like Chaplygin gas (CG) that drives cosmic acceleration when $ Q_m $ is negative, while for positive $Q_m$, it exhibits characteristics of a quintessence-like phase. From the perturbation evolution equations, the numerical results of $\delta(z)$ and $f\sigma_8(z)$ were used to explore structure growth. A comparison of the $H_0$ and $S_8$ values has been made of the $\Lambda$CDM and diffusive models across recent cosmological surveys to show the possibility of alleviating the cosmological tensions, though the detailed analysis is beyond the scope of the current study.

Speaker: Shambel Akalu (Centre for Space Research, North-West University)

9:50 AM Model-independent Constraints of Physics beyond ΛCDM with the Power Spectrum and Bispectrum

We apply model-independent methods based on symmetries — specifically the 'LSS bootstrap' — to derive robust predictions across a wide range of alternative scenarios to $\Lambda$CDM. Our ongoing work aims to improve constraints on bootstrap parameters, i.e., cosmology-dependent coefficients in the matter kernels, by jointly analyzing the power spectrum (up to one-loop) and the tree-level bispectrum. This analysis is implemented using the PyBird code and applied to both observational data from the BOSS survey and synthetic data from the PT Challenge simulations, which probe significantly larger volumes. We investigate whether the increased volume of the PT Challenge data leads to tighter constraints on bootstrap parameters, illustrating the potential of this model-independent framework for testing deviations from $\Lambda$CDM in ongoing and future galaxy surveys.

Speaker: Giorgia Biselli (Università di Parma)

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Dark energy-vs-high energy physics

11:00 AM Long lecture 3

Speaker: Cliff Burgess

2:00 PM → 3:30 PM Lecture: Gravitational Waves for Cosmology

2:00 PM Long lecture 1

Speaker: Daniele Steer

4:00 PM → 5:30 PM Hands-on

Thursday, July 10

9:00 AM → 10:30 AM Lecture: The standard model of cosmology: a critique of its status

9:00 AM Short lecture

Speaker: Pierre Fleury

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Dark energy-vs-high energy physics

11:00 AM Long lecture 4

Speaker: Cliff Burgess

2:00 PM → 3:30 PM Lecture: Physics of the dark ages

2:00 PM Long lecture 1

Speaker: Benoit Semelin

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Contributions

4:00 PM Warm inflation - a reflection of quantum gravity

The validity of popular cold and warm inflationary scenarios in cosmology is investigated by comparing and contrasting various models. Results indicate that warm inflation can provide a more realistic understanding of the early universe in the light of cosmic microwave background than the conventional cold inflation. The genesis of warm inflation from supersymmetry and string theory emphasise the role of quantum gravity in the early universe. The very nature of warm inflation requires the existence of multifields stemming from superstring theory and hence the warm inflation can be a reflection of quantum gravity.The effect of dissipation coefficient of warm inflation on the Hubble parameter and its role in accounting the Hubble tension is examined. The obtained result may support the dynamical dark energy as suggested by DESI DR2.

Speaker: Ms Anupama Balasubramanian (University Of Hyderabad)

4:25 PM Form Lambda to Lambdons: dynamical dark energy via symmetry breaking.

Amidst a myriad of sophisticated alternatives to general relativity, unimodular gravity stands unique as a relatively simple extension. In the Henneaux-Teitelboim (HT) formulation of unimodular gravity, the cosmological constant $\Lambda$ is promoted to a scalar field $\Lambda(x)$ at the level of the action. However, a non-dynamical vector density $\mathcal{T^{\mu}}$ ensures the constancy of $\Lambda$ on shell and consequently, the retention of the original Einstein field equations.

In 4 space-time dimensions, the vector density $\mathcal{T^{\mu}}$ can be interpreted as a topological 3-form gauge field which exists in a non-standard $U(1)$ representation. In the regular electrodynamics for a $U(1)$ gauge field $A_{\mu}$, the addition of a mass term or Proca term $m^{2}A_{\mu}A^{\mu}$ increases the internal d.o.f of $A_{\mu}$. Analogously, when $m^{2}\mathcal{T_{\mu}}\mathcal{T^{\mu}}$ is added to the HT action unimodular symmetry is broken. Curiously, $\mathcal{T^{\mu}}$ is still non-dynamical, rather, the scalar field $\Lambda(x)$ now obeys a wave equation. The Lambdon is born.

Based on:
https://arxiv.org/pdf/2305.09380
https://arxiv.org/pdf/2311.11160

Speaker: Raymond Isichei (Imperial College London)

4:50 PM Dynamical Cosmological Constant

In this work, we studied a model that dynamically realizes the equation of state $p + \rho = 0$ . The perturbations of such a system, which mimics a Dynamical Cosmological Constant (DCC), exhibit pathological behavior within the perfect fluid approximation. We show that going beyond the perfect fluid paradigm is essential for achieving a stable evolution and that the presence of an anisotropic stress term is necessary. The linear stability of the system in isolation requires the Hamiltonian to be non-positive definite, analogous to the case of the Pais–Uhlenbeck oscillator.

We analyze in detail the dynamics of linear cosmological perturbations in a DCC-dominated universe and demonstrate that when DCC is minimally coupled to gravity, no severe instabilities arise. Our results indicate that the non-relativistic matter density contrast is no longer constant $-$ as it is in the standard cosmological constant case $—$ but displays an oscillatory behavior at small scales and a mild growth at large scales. We also examine the gravitational wave sector, finding that at small scales the amplitude is still suppressed as an inverse power of the scale factor, while at large scales it grows logarithmically. Additionally, we find propagating modes in the vector sector, though no growing instabilities are present.

Speaker: Giuseppe Di Donato (Università dell' Aquila)

Friday, July 11

9:00 AM → 10:30 AM Lecture: Physics of the dark ages

9:00 AM Long lecture 2

Speaker: Benoit Semelin

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Physics of the dark ages

11:00 AM Short lecture

Speaker: Dominique Aubert

2:00 PM → 3:30 PM Lecture: Gravitational Waves for Cosmology

2:00 PM Long lecture 2

Speaker: Daniele Steer

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Contributions

4:00 PM Searching for Ultralight ALPs with JVLA and VLBA observations

Axionlike particles (ALPs) are promising candidates for dark matter. A tiny interaction between photons and ALPs gives rise to achromatic birefringence. The birefringence angle oscillates with a time-period determined by ALP mass. We exploit this property of ALPs to find stringent constraints on its coupling constant as well as mass by means of radio polarimetric observations of strong gravitationally lensed quasars.
The differential polarization angle measured between the images of strong gravitationally lensed quasars is expected to exhibit a clean ALP-induced birefringence signal which is free of observational and astrophysical systematics. This allows us to probe ALPs at sensitivity comparable to, or better than, lab-experiments. We demonstrate this new technique with the help of existing observations. We also report about the ongoing analysis of ∼100 hours of dedicated multi-epoch spectropolarimetric observations of 5 gravitational lens systems using the JVLA and the VLBA. This method probes ultralight ALPs of the order of $10^{-20}$ eV.

Speaker: Shivani Deshmukh (Bielefeld University)

4:25 PM From Galaxy clusters to the Epoch of Reionization, an exploration of what ML tools can bring to cosmology and simulations.

Machine Learning (ML) as emerged in the last decade as a powerful tool to solve complex, high-dimensional problems. This presentation will cover several aspects of my research related to ML techniques applied to tackle challenges in cosmology. Firstly, I will describe a new method to infer cosmological parameters from X-ray cluster number counts, using full-field emulation and simulation-based inference. Secondly, I will show how this framework can also be applied to radio interferometry, in order to constrain the HI fraction during the epoch of reionization (EoR). Lastly, I will present an alternative path to run cold dark matter simulations with Kolmogorov-Arnold Networks.

Speaker: Nicolas Cerardi (EPFL)

4:50 PM Constraining Pressure-Based Dark Energy Models with Latest Cosmological Data

In this talk, I explore an extension of the standard cosmological model by introducing a dynamical dark energy (DDE) scenario, where the pressure evolves with cosmic time. Instead of assuming a constant dark energy component, we expand the pressure around the present epoch to capture possible deviations from a cosmological constant. This approach introduces one or two new parameters, depending on the order of the expansion, which quantify how dark energy evolves over time. Using recent observational data, including Planck CMB, DESI galaxy clustering, and DESY5 supernovae, I present constraints on both first- and second-order DDE models. The results show significant evidence for dynamical behavior: a 2.7σ preference for the first-order model and over 4σ for the second-order case. In particular, the second-order reconstruction reveals a non-monotonic evolution of dark energy, including phantom-crossing behavior. Importantly, the inferred trends are consistent across datasets and align well with other dynamical parametrizations, stressing the robustness of this pressure-based framework. Based on 2505.02932 and ongoing work.

Speaker: Hanyu Cheng (Tsung-Dao Lee Institute & SJTU)

Monday, July 14

9:00 AM → 10:30 AM Lecture: Physics of the dark ages

9:00 AM Long lecture 3

Speaker: Benoit Semelin

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Contributions

11:00 AM Signatures of composite dark matter in the cosmic microwave background spectral distortions

We propose a new method to detect a class of composite dark matter models where the electromagnetic transitions between dark matter states result in spectral distortions in the Cosmic Microwave Background (CMB) spectrum. We show that the spectral distortion signature depends sensitively on the dark matter transition frequency and the strength of couplings of dark matter with the visible sector particles as well as its self-interactions, thus opening a new window to probe the nature of dark matter. The unique shapes of non-thermal distortions make them distinguishable from the standard μ and y-type distortions and potentially detectable in the next-generation experiments such as Primordial Inflation Explorer (PIXIE). We find that the spectral distortion limits from the COsmic Background Explorer/Far-Infrared Absolute Spectrophotometer (COBE/FIRAS) already give a constraint on the electromagnetic coupling of dark matter which is three orders of magnitude stronger compared to the current direct detection limits for ∼ MeV mass dark matter with transition energy in ∼ 1-10 eV range. Further, the upcoming 21 cm experiments will probe the non-thermal distortion signatures of dark matter in the 50-100 MHz range. We also show that the absorption of CMB photons by dark matter in the 100-200 GHz frequency range can explain the strong absorption feature detected by the Experiment to Detect the Global Epoch of Reionization Signal (EDGES) collaboration.

Speaker: Anoma Ganguly (University of Arizona)

11:25 AM Forward modelling UNIONS survey for Implicit Likelihood Inference

The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a photometric survey in the North. Its images can be used to study the Large-Scale structure of the Universe with cosmic shear. The standard approach relies on two-point statistics that only capture the Gaussian information in the shear field. Statistics can be build to extract its non-Gaussian information but usually relie on numerical simulations. Bridging the gap between model and data requires a realistic forward modelling of the UNIONS survey. It includes accounting for astrophysical systematics but also survey specific properties. In this talk, I will present the ongoing effort to build a realistic forward model for UNIONS survey and its use for Implicit Likelihood Inference.

Speaker: Sacha Guerrini (CEA Paris-Saclay/CosmoStat)

11:50 AM Smooth sailing or ragged climb? — Increasing the robustness of power spectrum de-wiggling and ShapeFit parameter compression

ShapeFit is a novel approach alternative to Full Modeling, and has been gaining popularity for analyzing the large scale structures of the universe. This approach provides information on the slope of the matter power spectrum at the pivot scale, m. There are two crucial steps to obtain this additional information: de-wiggling the power spectrum and calculating the derivative at the pivot scale. In this work different de-wiggling and derivative methods were compared and examined to study their impact on the obtained value of the slope. A systematic uncertainty of σ = 0.023|m| + 0.001 is derived by studying the behavior of the slope values in different cosmologies within and beyond LCDM.

Speaker: Katayoon Ghaemiardakani (CPPM)

2:00 PM → 3:30 PM Lecture: Physics of the dark ages

2:00 PM Short lecture

Speaker: Marian Douspis (IAS)

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:40 PM Contributions

4:00 PM Interpretable Neural Networks for testing Beyond-ΛCDM scenarios with CMB and Large-Scale Structure Data

The era of precision cosmology has provided an unprecedented opportunity to test fundamental physics using Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS) data. In this talk, I will present our recent work on applying neural networks (NNs) for cosmological model selection, focusing on two case studies: CMB power spectra from Planck 2018 data and galaxy clustering surveys. Our approach explores the ability of NNs to distinguish between the standard ΛCDM model and beyond-ΛCDM scenarios, including modified gravity (Hu-Sawicki f(R)) and inflationary feature models. A key aspect of our methodology is the implementation of interpretability tools, such as SHAP and LIME, to identify the most relevant features driving the model classification. Our results demonstrate that NNs can achieve high accuracy in discriminating between models, while interpretability techniques help reveal some key physical processes governing these scenarios. These findings highlight the potential of machine learning to enhance cosmological inference and pave the way for its integration into next-generation surveys.

Speaker: Ms Indira Ocampo (Instituto de Física Teórica UAM-CSIC)

4:25 PM Cosmology from the Rubin Void Size Function

Cosmic voids are a powerful tool to extract cosmological constraints and study galaxy properties’ dependence on the environment. The project develops a pipeline to constrain cosmological parameters using the Void Size Function (VSF) derived from LSST-like galaxy mock catalogs, employing the VIDE void finder. The analysis incorporates a theoretical model accounting for tracer bias, redshift-space distortions, and the Alcock-Paczynski effect. For the first time, theoretical predictions for the void size function is compared to measurements from photometric redshift data, enabling an assessment of statistical and systematic photometric uncertainties. The resulting constraints targeted are key cosmological quantities such as the dark energy equation of state, matter clustering amplitude (σ₈), dark matter density, total neutrino mass, and overall cosmic content.

Speaker: Pierre Boccard (Centre de Physique de Particules de Marseille (CPPM))

4:50 PM Accurate Small Scale Dynamics in COLA.

Ongoing galaxy surveys map the Universe’s large-scale structure with unprecedented fidelity across immense cosmological volumes. Cosmological inference at the field level demands thousands of N-body simulations. To fully exploit Stage-IV data, simulators must therefore produce fast, high-precision realisations spanning vast cosmological volumes and reaching deep into the non-linear regime. The COmoving Lagrangian Acceleration (COLA) algorithm accelerates large-scale cosmological simulations by decoupling the temporal evolution of large and small scales: large scales are evolved analytically using Lagrangian Perturbation Theory (LPT), while small scales are integrated numerically. Contrary to a common misconception, COLA does not inherently sacrifice small-scale accuracy for speed: the LPT change of frame of reference can be done with any force calculation technique. I show that accurate small-scale dynamics can be obtained at a tractable computational cost by employing Particle–Particle–Particle–Mesh (P3M) force evaluations within an LPT frame of reference, achieving the precision of tree-based codes down to scales of just a few particle lengths. This result is a significant advance towards fully harnessing the cosmological potential of Stage-IV galaxy surveys.

Speaker: Tristan Hoellinger (Institut d'Astrophysique de Paris)

Tuesday, July 15

9:00 AM → 10:30 AM Lecture: Numerical cosmology

9:00 AM Long lecture 1

Speaker: Romain Teyssier

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Gravitational Waves for Cosmology

11:00 AM Short lecture

Speaker: Chiara Caprini

2:00 PM → 3:30 PM Hands-on

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:00 PM Contributions

4:00 PM Turning dispersion into signal: Density-split analyses of pairwise velocities

Pairwise velocities of the large-scale structure encode valuable information about the growth of structure. They can be observed indirectly through redshift-space distortions and the kinetic Sunyaev–Zeldovich effect. Whether Gaussian or non-Gaussian, pairwise velocity has a broad distribution, but the cosmologically useful information lies primarily in the mean — the streaming velocities; the dispersion around the mean is often treated as a nuisance. This conventional approach reduces the constraining power of our observations. Here, we show that this does not have to be the case, provided the physics behind the dispersion is understood. By splitting the halo/galaxy samples according to their density environments and measuring the streaming velocities separately, we demonstrate that the total signal-to-noise is several times greater than in conventional global measurements of the pairwise velocity distribution (PVD). By splitting the data, we avoid cancellation between these opposing velocities, effectively turning what would be considered dispersion in the global PVD into a signal. Our findings indicate substantial potential for improving the analysis of PVD observations using the kinetic Sunyaev-Zeldovich effect and redshift-space distortions.

Speaker: Aritra Gon (University of Edinburgh)

4:25 PM A catalog of high significance cosmic voids in the Local Universe

Cosmic voids are the largest objects emerging in the cosmic web, covering the majority of the volume of the Universe. They are a well-established probe to gather cosmological information from the large-scale structure, as well as interesting regions to study how the underdense environment affects the behavior of astrophysical objects. Unfortunately, identifying voids in a galaxy catalog is challenging for multiple reasons: observational effects such as holes in the mask or magnitude selection hinder the detection process; galaxies are biased tracers of the underlying dark matter distribution; and it is non-trivial to estimate the detection significance and parameter uncertainties for individual voids.
We use a set of constrained simulations of the large-scale structure that are consistent with the observed galaxy positions, effectively representing statistically independent realizations of the probability distribution of the cosmic web. We run the VIDE void finding algorithm on each individual simulation, and compare the detected voids to identify regions that are voids with high statistical significance. As this framework is fully Bayesian, we evaluate the probability distributions of the centers and radii of the voids. Finally, we characterize the actual shape of these regions, resulting in a template for density environments that can be used in astrophysical applications, e.g. studying the evolution of galaxies. We plan to make the resulting catalog of high-significance voids and their properties publicly available.

Speaker: Rosa Malandrino (Institut d'Astrophysique de Paris)

5:00 PM → 6:30 PM Lecture: Gravitational Waves for Cosmology

5:00 PM Short lecture

Speaker: Nicola Tamanini

Wednesday, July 16

9:00 AM → 10:30 AM Lecture: Numerical cosmology

9:00 AM Long lecture 2

Speaker: Romain Teyssier

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Numerical cosmology

11:00 AM Short lecture

Speaker: Katarina Kraljic

2:00 PM → 3:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

2:00 PM Short course

Speaker: Elisabeth Krause

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Hands-on

Thursday, July 17

9:00 AM → 10:30 AM Lecture: Numerical cosmology

9:00 AM Long lecture 3

Speaker: Romain Teyssier

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Gravitational Waves for Cosmology

11:00 AM Short lecture

Speaker: Tania Regimbau

2:00 PM → 3:30 PM Lecture: Numerical cosmology

Friday, July 18

9:00 AM → 10:30 AM Lecture: Numerical cosmology

9:00 AM Long lecture 4

Speaker: Romain Teyssier

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Numerical cosmology

11:00 AM Short lecture

Speaker: Oliver Hahn

2:00 PM → 3:30 PM Lecture: Numerical cosmology

2:00 PM Short lecture

Speaker: Raul Angulo

Monday, July 21

9:00 AM → 10:30 AM Lecture: Advanced CMB physics

9:00 AM Long lecture 1

Speaker: Julien Lesgourgues

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Long lecture 1

Speaker: Cora Uhlemann

2:00 PM → 3:30 PM Lecture: Advanced CMB physics

2:00 PM Short course

Speaker: Giulio Fabbian

Tuesday, July 22

9:00 AM → 10:30 AM Lecture: Advanced CMB physics

9:00 AM Long lecture 2

Speaker: Julien Lesgourgues

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Long lecture 2

Speaker: Cora Uhlemann

2:00 PM → 3:30 PM Lecture: Advanced CMB physics

2:00 PM Short course

Speaker: Silvia Galli (IAP)

4:00 PM → 5:30 PM Hands-on

Wednesday, July 23

9:00 AM → 10:30 AM Lecture: Advanced CMB physics

9:00 AM Long lecture 3

Speaker: Julien Lesgourgues

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Long lecture 3

Speaker: Cora Uhlemann

2:00 PM → 3:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

2:00 PM Short course

Speaker: Clotilde Laigle

4:00 PM → 5:30 PM Hands-on

Thursday, July 24

9:00 AM → 10:30 AM Lecture: Advanced CMB physics

9:00 AM Long lecture 4

Speaker: Julien Lesgourgues

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Long lecture 4

Speaker: Cora Uhlemann

2:00 PM → 3:30 PM Lecture: Advanced CMB physics

2:00 PM Short course

Speaker: Cyril Pitrou

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Contributions

4:00 PM Identification of Protohalos with Deep Learning

The gravitational collapse of dark matter halos from small density perturbations in the early universe is a highly stochastic and non-linear process that is best approximated through N-body simulations. In this work, we test and compare the ability of fully-convolutional neural networks and transformer-based neural networks to predict the formation of dark matter halos from initial conditions, and classify the detected protohalos according to their final mass at redshift $z=0$. We find that the transformer-based model outperforms the CNN-based model substantially, achieving $<1\%$ error on the level of the whole simulation box, and $<10\%$ error on the level of individual objects. We also test the possibility of getting some physical insights into the training process.

Speaker: Toka Alokda (Argelander Institute for Astronomy, University of Bonn)

4:25 PM LADDER: Revisiting the Cosmic Distance Ladder with Deep Learning Approaches and Addressing Cosmological Tensions

I'll present the prospects of reconstructing the "cosmic distance ladder" of the Universe using our novel deep learning framework, LADDER (Learning Algorithm for Deep Distance Estimation and Reconstruction). Trained on apparent magnitude data from the Pantheon Type Ia supernovae compilation, LADDER uses full covariance information among data points to deliver predictions with corresponding uncertainties. Extensive validation tests across multiple deep learning models confirmed LADDER as the best-performing one. I'll demonstrate some applications of this framework in cosmology, including its use as a model-independent tool for consistency checks for other datasets such as baryon acoustic oscillations (BAO), model-agnostic calibration of high-redshift datasets like gamma-ray bursts, and as a model-independent mock catalogue generator for future probes. Additionally, I will show how LADDER can serve as a model-independent recalibration tool for different BAO datasets, helping to alleviate the Hubble and clustering tensions. Our analysis highlights the value of model-independent techniques and underscores the need for cautious yet innovative machine learning applications in cosmological contexts.

This would be based on the following papers,
(1) Astrophys. J. Suppl. Ser. 273(2), 27 (2024); arXiv:2401.17029.
(2) arXiv:2412.14750.

Speaker: Mr Rahul Shah (Indian Statistical Institute, Kolkata)

4:50 PM A New Mechanism for Dynamical Dark Energy in Light of DESI Observations

Recent results from the DESI survey provide compelling evidence for a dynamical dark energy component, challenging the long-standing cosmological constant paradigm. In this talk, I will present a mechanism based on chameleon dark energy—an interacting quintessential scalar field dark energy and dark matter model mediated by a Yukawa-type coupling. This fifth-force framework not only allows for a natural phantom crossing in the dark energy equation of state, as favored by DESI data, but also offers the first statistically significant detection of dark sector interaction. I will discuss the theoretical foundation of this model and its observational signatures, emphasizing how it aligns with the latest DESI constraints.

Speaker: Mr Amlan Chakraborty (Indian Institute of Astrophysics)

Friday, July 25

9:00 AM → 10:30 AM Lecture: Advanced CMB physics

9:00 AM Long lecture 5

Speaker: Julien Lesgourgues

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Short course

Speaker: Florent Leclercq (Institut d'Astrophysique de Paris)

Monday, July 28

9:00 AM → 10:30 AM Lecture: Standard model tensions

9:00 AM Long lecture 1

Speaker: Vivian Poulin

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Short course

Speaker: Azadeh Moradinzehad

2:00 PM → 3:30 PM Lecture: Standard model tensions

2:00 PM Long lecture 1

Speaker: Eleonora di Valentino

Tuesday, July 29

9:00 AM → 10:30 AM Lecture: Standard model tensions

9:00 AM Long lecture 2

Speaker: Eleonora di Valentino

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Hands-on

2:00 PM → 3:30 PM Lecture: Standard model tensions

2:00 PM Long lecture 2

Speaker: Vivian Poulin

Wednesday, July 30

9:00 AM → 10:30 AM Lecture: Dark matter alternatives

9:00 AM Long lecture 1

Speaker: Ludovic van Waerbeke

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Large scale structures of the universe: physics, phenomenology, statistics

11:00 AM Short course

Speaker: Francois Lanusse (CNRS)

2:00 PM → 3:30 PM Lecture: Dark matter alternatives

2:00 PM Short course

Speaker: Eric Armengaud

Thursday, July 31

9:00 AM → 10:30 AM Lecture: Dark matter alternatives

9:00 AM Long lecture 2

Speaker: Ludovic van Waerbeke

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Lecture: Dark matter alternatives

11:00 AM Short course

Speaker: Benoit Famaey

2:00 PM → 3:30 PM Hands-on

Friday, August 1

9:00 AM → 10:30 AM Lecture: Dark matter alternatives: Long lecture 3

Convener: Ludovic van Waerbeke

10:30 AM → 12:00 PM Hands-on