COLOURS

Session

COLOURS Workshop

10 juin 2025, 09:30

Institut Pascal

Présidents de session

COLOURS Workshop: Opening

• Samuel Farrens (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session I

• Samuel Farrens (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session II

• Ottavia Truttero (University of Edinburgh)

COLOURS Workshop: Session III

• Katayoon Ghaemiardakani (CPPM)

COLOURS Workshop: Session IV

• Vineshree Pillay (University of Cape Town)

COLOURS Workshop: Session V

• Emma Ayçoberry (CEA / DAp)

COLOURS Workshop: Session VI

• Julien Tang (LBNL/CPB)

COLOURS Workshop: Session VII

• Fabian Hervas Peters (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session VIII

• Romain Paviot (CEA Paris-Saclay)

COLOURS Workshop: Session IX

• Sacha Guerrini (CEA Paris-Saclay/CosmoStat)

COLOURS Workshop: Session X

• Ezequiel Centofanti (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session XI

• Andreas Tersenov (IA&ICS - FORTH)

COLOURS Workshop: Session XII

• Natalia Porqueres (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session XIII

• Vilasini Tinnaneri Sreekanth (CosmoStat, CEA Paris-Saclay)

COLOURS Workshop: Session XIV

• Leonor Simões (University College London)

21. Welcome

Samuel Farrens (CosmoStat - CEA Paris-Saclay)

10/06/2025 09:30

22. Keynote - Overview of the ESA Euclid mission in the context of ESA Science today

Valeria Pettorino (ESA ESTEC)

10/06/2025 09:40

After a brief introduction of the ESA Science programme I will focus on an overview of the ESA Euclid mission: I will describe mission objectives, challenges, main milestones so far, the first data release.

I will also mention a few ESA programmes dedicated to interns, graduate students, and postdocs.

24. Suppressing the Growth of Structure with Modified Gravity Theories

Linus Thummel (University of Edinburgh)

10/06/2025 10:20

Modifications of General Relativity have been widely studied to alleviate cosmological tensions. Most of these models lead to an effective strengthening of gravity and enhanced growth. However, the S8 tension — arising from weak-lensing observations that suggest less structure formation than predicted by ΛCDM — points to a different scenario. In this talk, we investigate stable subclasses of...

70. Investigating the Evolution of the Universe Using the observational H(z) data (OHD): Constraining Cosmological Parameters, Dark Energy, and the Hubble Constant

Jing Niu (School of Physics and Astronomy, Beijing Normal University)

10/06/2025 10:40

We use the Cosmic Chronometers H(z) data, also the observational H(z) data (OHD), to investigate the universe's evolution, focusing on its applications in constraining cosmological parameters, probing dark energy, and refining methods for determining the Hubble constant (H0). (1) To improve cosmological model selection, we combine H(z) with fσ8(z), comparing the traditional chi-square approach...

25. Detecting Relativistic Doppler by Multi-tracing a Single Galaxy Population

Federico Montano (University of Turin)

10/06/2025 11:30

The detection of relativistic Doppler via galaxy power spectrum measurements could further confirm the validity of general relativity at scales very far from the strong-gravity-field regime, where it has been tested with exquisite accuracy. The Doppler term acts as an imaginary correction in the relation between the galaxy density contrast and that of matter, which mostly affects the large...

26. Accuracy of HOD models for stage IV surveys

Romain Paviot (CEA Paris-Saclay)

10/06/2025 11:50

58. Probing Inflation with PICO: Simulations and Delensing for CMB B-Modes

Julien TANG (LBNL/CPB)

10/06/2025 12:10

The polarized cosmic microwave background (CMB) signal can be decomposed into parity-even E-modes and parity-odd B-modes. The inflationary signal would manifest itself as a B-mode signal. An inflationary period at the beginning of the Universe imprints a B-mode signal in the polarization of the CMB and if the energy scale of inflation is large enough the signal may be detectable. At a maximum...

28. Autoencoders for AGN identification in the DESI Y3 survey

Dhavala Sai Srinivas (University of Portsmouth)

10/06/2025 12:30

We describe a machine learning approach to multi-wavelength Active galactic nuclei (AGN) identification for host galaxies within the DESI survey. AGNs emit light in all wavelengths in the electromagnetic spectrum, it is difficult to create an AGN selection that is fully complete. The identification of AGNs is key to understanding not only their astrophysics, being an important driver of galaxy...

29. Keynote - Latest cosmological results from DESI

Pauline Zarrouk (CNRS/LPNHE)

10/06/2025 14:50

30. Relativistic effects in galaxy clustering with DESI

Jade Piat (University of Edinburgh)

10/06/2025 15:30

Understanding the accelerated expansion of the Universe remains as one of the key challenges in cosmology. The main candidates to explain this observation, which do not rely on a cosmological constant, are dark energy and modifications of General Relativity, but they require robust tests on cosmological scales. The Dark Energy Spectroscopic Instrument offers unprecedented precision in...

31. Densitysplit for the DESI BGS

Simon Bouchard (LPNHE)

10/06/2025 15:50

The Bright Galaxy Survey (BGS) is the densest galaxy sample of the DESI project, and the closest in redshift range (z<0.2). At such small redshift, the constraint on cosmological parameters is dominated by the "cosmic variance", a statistical error due to the small volume of universe considered. Alternative clustering analysis methods, such as Density-Split or Multi-Tracer analysis have shown...

32. Model-agnostic assessment of dark energy after DESI DR1 BAO

BIKASH RANJAN DINDA (University of the Western Cape)

10/06/2025 16:40

Baryon acoustic oscillation measurements by the Dark Energy Spectroscopic Instrument (Data Release 1) have revealed exciting results that show evidence for dynamical dark energy at around 3sigma when combined with cosmic microwave background and type Ia supernova observations. These measurements are based on the w0waCDM model of dark energy. The evidence is less in other dark energy models...

78. Spectral Inpainting with Diffusion Models: A Novel Approach for Continuum Removal in Euclid Data

Domingos Savio Pinheiro do Nascimento Junior (Politecnico di Milano/INAF)

10/06/2025 17:00

The accurate characterization of galaxy spectra is essential for extracting reliable physical properties of galaxies. However, overlapping of spectra inherent to Euclid’s slitless spectroscopy can often obscure key spectral features, complicating the detection and analysis of emission lines.
In this work, we present a novel approach for continuum removal by leveraging denoising diffusion...

35. Keynote - Reconstructing the Universe's history with projected large-scale structure data

David Alonso (University of Oxford)

11/06/2025 09:40

36. The Fink broker: a personalized window to the transient sky through LSST

Emille Ishida (CNRS/LPCA)

11/06/2025 10:20

The Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will provide an unprecedented volume of time-domain data opening a new era of big data in astronomy. To fully harness the power of these surveys, we require analysis methods capable of dealing with large data volumes that can identify promising transients within minutes for follow-up coordination. In this talk I will present...

53. Latest perspectives on weighing neutrinos with 21cm intensity mapping at the SKAO

Gabriele Autieri (SISSA, INFN Trieste, IFPU)

11/06/2025 10:40

The large-scale distribution of neutral hydrogen in the late Universe, mapped through the hydrogen 21cm line emission using radio telescopes, holds significant potential to emerge as a key cosmological probe in the coming years. In the work that I’m going to present, we developed a Gaussian likelihood code for the 21cm intensity mapping power spectrum and the 21cm-galaxy clustering...

38. Baryon-free S8 tension with stage IV cosmic shear surveys

Ottavia Truttero (University of Edinburgh)

11/06/2025 11:30

Accurately modelling matter power spectrum effects at small scales, such as baryonic feedback, is essential to avoid significant bias in the estimation of cosmological parameters with cosmic shear. However, Stage IV surveys like LSST will be so precise that significant information can still be extracted from large scales alone. In this talk, I will present an analysis of LSST Year 1-like mock...

39. Growth of structure using cross-correlation of CMB lensing and cosmic shear

Shabbir Shaikh (Arizona State University)

11/06/2025 11:50

Weak lensing of cosmological sources is an important tool for studying the distribution of total matter in the universe. Cross-correlating weak lensing of the Cosmic Microwave Background (CMB) with weak lensing of galaxies ("cosmic shear") allows a way to place robust constraints on the amplitude of matter perturbations in the universe while minimizing the impact of certain systematic effects...

41. Probing the Cosmological Principle with weak lensing shear

James Adam (University of the Western Cape)

11/06/2025 12:10

The Cosmological Principle is a cornerstone of the standard model of cosmology and shapes how we view the Universe and our place within it. It is imperative, then, to devise multiple observational tests which can identify and quantify possible violations of this foundational principle. One possible method of probing large-scale anisotropies involves the use of weak gravitational lensing. In...

75. Shear calibration for UNIONS

Fabian Hervas Peters (CosmoStat, CEA Paris-Saclay)

11/06/2025 12:30

42. Keynote - Weak lensing and 3x2pt with Euclid

Alex Hall (University of Edinburgh)

11/06/2025 14:50

Euclid is a European Space Agency telescope designed to map the dark Universe and uncover the nature of cosmic acceleration. It is conducting a large survey of galaxies, which will be used to measure the large-scale mass distribution of the Universe through weak gravitational lensing, galaxy clustering, and their combination ('3x2pt'). I will explain how we plan to use Euclid's imaging to...

43. ElFNet: Ellipticity Finding Network

Lucy Reynolds (Institut de Física d'Altes Energies (IFAE))

11/06/2025 15:30

Noise bias is a persistent challenge in shear measurements, particularly for galaxies with low signal-to-noise ratios (SNR), which are critical for Euclid’s cosmic shear analysis. To address this, we present a novel, unsupervised, deep learning denoising technique (ElFNet) to improve galaxy shape measurements. Using a convolutional neural network (CNN), we predict individual galaxy shears...

44. Staying focused: In-flight monitoring of the Euclid space telescope

Dennis Neumann (Leiden Observatory)

11/06/2025 15:50

The Euclid survey was the first Stage IV survey to be commissioned, paving the way for a new era of precision cosmology. The survey's declared scientific goal is to explore the nature of dark matter and dark energy. One of the main probes it utilises is weak gravitational lensing: the coherent distortion of galaxy shapes caused by the large-scale structure of the Universe. Over its lifespan,...

45. Impact of Weak Lensing Mass Mapping Algorithms on Cosmology Inference

Andreas Tersenov (IA&ICS - FORTH)

11/06/2025 16:40

Weak gravitational lensing provides a powerful probe of dark matter distribution in the Universe. Mass mapping algorithms, which reconstruct the convergence field from galaxy shear measurements, are critical for extracting higher-order statistics to constrain cosmological parameters. This study evaluates the impact of different mass mapping algorithms—Kaiser-Squires, inpainting Kaiser-Squires,...

46. Higher-Order Weak Lensing Statistics in Euclid: insights from pre-launch projects and DR1 plans

Filippo Bouchè (Scuola Superiore Meridionale & INFN Sez. Napoli)

11/06/2025 17:00

I will provide an overview of higher-order weak lensing statistics and their relevance to the Euclid mission. The talk will draw on the results of the pre-launch Paper 2, which employed the Fisher formalism to explore the constraining power of these non-Gaussian statistics on cosmological parameters. Emphasis will be placed on the key lessons learned from this preparatory project, highlighting...

47. Weak lensing higher-order statistics in f(R) gravity

Alessandro Vadalà (INAF - Astronomical Observatory of Rome)

11/06/2025 17:20

The problems within the standard cosmological model have sparked the research of alternatives and possible solutions and one way to tackle these problems is to question the validity of General Relativity (GR) as the correct theory of gravitation on cosmological scales, entering the context of modified gravity (MG) theories. In this work, we studied a specific MG model known as f(R) gravity, in...

48. Keynote - Cosmology from Radio Continuum Surveys

Catherine Hale (University of Oxford)

12/06/2025 09:40

Surveys from modern radio telescopes, such as the precursor/pathfinder telescopes for the Square Kilometre Array Observatory (SKAO) are currently transforming the knowledge which we have of the radio skies. Telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP), Low Frequency Array (LOFAR) and MeerKAT are producing a number of radio continuum surveys which have a...

76. Theoretical Predictions for Wavelet ℓ1-Norm in Weak Lensing

Vilasini Tinnaneri Sreekanth (CosmoStat, CEA Paris-Saclay)

12/06/2025 10:20

50. Primordial non-Gaussianity - the effects of relativistic and wide-angle corrections to the power spectrum

Sêcloka Lazare Guedezounme (University of the Western Cape)

12/06/2025 10:40

Wide-angle and relativistic corrections to the Newtonian and flat-sky approximations are important for accurate modelling of the galaxy power spectrum of next-generation galaxy surveys. In addition to Doppler and Sachs-Wolfe relativistic corrections, we include the effects of lensing convergence, time delay and integrated Sachs-Wolfe. We investigate the impact of these corrections on...

51. Keynote - Mapping Neutral Hydrogen: opportunities and challenges on the road to the SKA Observatory

Marta Spinelli (Observatoire de la Cote d'Azur)

12/06/2025 11:30

Intensity Mapping techniques for the 21cm line. In the post-reionization era (z < 6), this will allow us to trace the underlying large-scale distribution of matter, opening a new window on dark matter and dark energy. To unlock the full potential of this technique for the SKAO, an intense data-taking campaign has been carried out using the SKAO precursors. I will describe the status of...

52. Detection of the power spectrum turnover with SKA & some galaxy surveys

Yolanda Dube (University of the Western Cape)

12/06/2025 12:10

Understanding the universe at ultra-large scales offers a unique window into its origins and evolution, particularly the transition from radiation to matter domination. The power spectrum turnover, a subtle yet critical feature of large-scale structure, holds the key to unraveling these mysteries. In this study, we explore the potential of next-generation surveys, including the Square...

37. Probing Neutrino Mass using the Cosmic Web

Leonor Simões (University College London)

12/06/2025 12:30

We explore the effects of massive neutrinos and baryons on the cosmic web using the FLAMINGO simulations. With NEXUS+, we classify the cosmic web into voids, sheets, filaments, and clusters, and find that massive neutrinos affect the environment by decreasing the amount of filaments and sheets. The effect of baryons is 10% smaller. Constructing the minimum spanning tree (MST) from the haloes...

54. Keynote - SPT-3G

Silvia Galli (IAP)

12/06/2025 14:50

56. The impact of dark energy on the thermal Sunyaev-Zel'dovich effect

Emma Ayçoberry (CEA / DAp)

12/06/2025 15:30

The distribution of matter in the Universe is a powerful probe of cosmology. Measuring the efficiency with which gravity produces clusters against expanding Universe is the key to understanding, e.g. the equation of state of dark energy. The thermal Sunyaev-Zel’dovich (tSZ) effect, being sensitive to the baryonic content of the Universe, also shows sensitivity to dark energy. In this work, I...

79. Follow up on COLOURS School communication exercise

Samuel Farrens (CosmoStat, CEA Paris-Saclay)

12/06/2025 15:50

59. Pannel discussion with Keynote speakers - What did we learn in Stage III? What do we hope to learn in Stage IV? What do we expect for the future?

12/06/2025 17:00

60. Keynote - DES

Daniel Gruen (LMU Munich)

13/06/2025 09:40

61. Dark Energy Survey Year 6: Magnification modeling and impact on galaxy clustering and weak lensing cosmology

Elisa Legnani (IFAE Barcelona)

13/06/2025 10:20

Gravitational lensing magnification affects the observed spatial distribution of galaxies and must be accounted for to avoid biases in cosmological probes of large-scale structure. I will present the methodology used to evaluate its impact on the Dark Energy Survey Year 6 (DES Y6) galaxy clustering and galaxy-galaxy lensing analyses. We quantify the redshift-dependent magnification bias using...

63. The future of cosmological inference

Alessio Spurio Mancini (Royal Holloway - University of London)

13/06/2025 10:40

In this talk I will introduce a new paradigm for cosmological inference, enabled by recent advances in machine learning and its underlying technology. By combining emulation, differentiable and probabilistic programming, scalable gradient-based sampling, and decoupled Bayesian model selection, this framework scales to extremely high-dimensional parameter spaces and enables complete Bayesian...

77. Forward modelling UNIONS survey for Implicit Likelihood Inference

Sacha Guerrini (CosmoStat, CEA Paris-Saclay)

13/06/2025 11:30

64. Machine learning in cosmology: Using emulators to accelerate inference for Stage-IV surveys

Ivan Sladoljev (Royal Holloway)

13/06/2025 11:50

In my talk, I will talk about the development of a large emulator library, designed to streamline the exploration and inference of different cosmological models being used in the Stage-IV survey analysis. This library serves as a bridge between different theoretical predictions and observational data, offering fast, accurate interpolations of key cosmological quantities. Built upon a suite of...

66. Forward-modelling Stage IV galaxy surveys for precise cosmological measurements

Luca Tortorelli (LMU Munich)

13/06/2025 12:10

Stage IV experiments are set to provide the stringent constraints ever on cosmological parameters. However, to achieve this aim, we need careful control of the systematics, especially those related to the accurate knowledge of the tomographic redshift distributions. The forward-modelling of photometric and spectroscopic galaxy surveys, a method that bridges cosmology with galaxy evolution,...

69. Closing

Samuel Farrens (CosmoStat - CEA Paris-Saclay)

13/06/2025 12:30