Cosmic Rhythms

8 Sept 2026, 09:00 → 12 Sept 2026, 17:00 America/Sao_Paulo

Auditório Ministro João Alberto Lins e Barros (CBPF)

Felipe Falciano, Gabriela A. Marques (CBPF), Guilherme Brando (CBPF), Louis Legrand (Centro Brasileiro de Pesquisas Fisicas), Mariana Penna Lima (UnB), Martin Makler, Miguel Quartin (CBPF)

The Cosmic Rhythms workshop aims to bring together international experts to discuss challenges in the upcoming era of high-precision cosmology, with a particular focus on large-scale structure, the CMB and their cross-correlations.

Topics will include data analysis, statistical methods, and theoretical modeling in light of the latest observations challenging the LCDM paradigm.

The workshop will take place on the 8 to 12 of September 2026 at the Brazilian Center for Research in Physics (CBPF) in Rio de Janeiro. CBPF is one of Brazil’s leading cosmology institutes, offering a fantastic setting near the Sugarloaf Mountain and just a few minutes from Copacabana Beach.

Preliminary Program

A preliminary program is now available here.

 

Participation & Contributions

Participation in the workshop is limited. Interested participants must apply to attend via the Indico registration form.

Scientific contributions will be selected from submitted abstracts. Accepted contributions may be presented either as oral talks or as posters. Poster presenters will also be invited to give a fire slide, consisting of a short 3-minute presentation to advertise their poster and highlight their research interests.

 

Important dates:

• 15th of January: Registration and abstract submission opening
• 15th of March 22nd of March: Deadline for abstract submission
• 30th of March: April 13: Selection of speakers and scientific program
• May 15: registration deadline
• May 21: Payment opens
• June 15: Payment deadline

 

Registration fees and payment:

* 1000 reais (~200 USD)

Registration and payment must be completed exclusively through the PayPal platform. The billing information provided by the participant during registration will be used by Fundação de Apoio e Desenvolvimento da Computação Científica (FACC) for invoice issuance. Please ensure that all billing details are entered correctly, as invoices cannot be modified or reissued with different information after payment confirmation.

Payments are processed via PayPal and may be made by credit card, subject to PayPal’s operational rules and availability. Depending on the payment method and country, additional banking or transaction fees may apply.

Please note that FACC will only issue invoices for registrations completed through the official PayPal registration system. Registrations made outside the platform will not be eligible for invoice issuance.

Cancellation Policy:

Participants may request cancellation and a refund within 7 days after payment confirmation.

Please note that refunds will not be issued in full. Banking fees, PayPal transaction fees, and FACC service charges will be deducted from the refunded amount.

In the case of cancellation requested by the participant, FACC will retain 10% of the registration fee to cover operational and administrative expenses.

If the cancellation is due to reasons attributable to the organizing institution, the registration fee will be refunded in full.

If a registration is completed after the official registration deadline established on the platform, the full amount paid will be refunded to the participant.

 

 

If you need any information please do not hesitate to contact us: cosmicrhythmscbpf@gmail.com

Local Organizing Committee:

• Gabriela Marques
• Louis Legrand
• Guilherme Brando
• Martin Makler
• Miguel Quartin
• Felipe Tovar

Scientific Organizing Committee:

• Clécio De Bom – CBPF
• Felipe Tovar – CBPF
• Gabriela Marques – CBPF
• Guilherme Brando – CBPF
• Louis Legrand – CBPF
• Raul Abramo – USP
• Mariana Penna Lima – UnB
• Martin Makler – CBPF
• Miguel Quartin – CBPF
• Nelson Pinto Neto – CBPF
• Valerio Marra – UFES

 

For more information about the COSMO group at CBPF, please visit: https://cbpf-cosmo.github.io/index_english.html

 

Cosmic_Rhythms_Preliminary_program_v2.pdf

Tuesday 8 September

CMB I

1 Blake Sherwin: ACT lensing DR6 plus

Speaker: Blake Sherwin

2 Giulio Fabbian: Cross-correlations CMB x Euclid

Speaker: Giulio Fabbian (Institut d'Astrophysique Spatiale)

10:30 Coffee break

3 Probing High-Redshift Structure Growth with CMB Lensing–Quasar Cross-Correlations

Recent and upcoming CMB experiments are opening a new window onto the late-time Universe by reaching arcminute-scale resolution. These improvements allow us to extract information from CMB secondary anisotropies, which probe the evolution and distribution of structure over most of cosmic history. I will present new constraints on the amplitude of matter fluctuations over a broad redshift range, obtained by combining CMB lensing observations from ACT DR6 and Planck PR4 with quasars from the Quaia catalogue. By analysing the CMB lensing and quasar overdensity auto-correlations together with their cross-correlation, we are able to put a 12% constraint on the amplitude of matter fluctuations at redshift z~5; which constitutes one of the highest redshift measurements of structure growth to date.

Speaker: Carmen Embil Villagra (University of Cambridge)

4 Cosmology from the cross-correlation of DESI DR2 galaxies and CMB lensing

I will present cosmological results obtained from the cross-correlation of DESI DR2 spectroscopic galaxies with CMB lensing reconstructions from ACT and Planck. This combination of galaxy surveys and CMB lensing provides powerful, percent level constraints on the growth of structure over a wide range of redshifts from $z=0.1$ to $z=2.1$. We further extend the redshift coverage of our analysis with the inclusion of the CMB lensing auto-correlation, reconstructing matter density perturbation out to $z\gtrsim 5$. By combining with Baryon Acoustic Oscillations (BAO), primary CMB observations, and other cosmological proves we place tight constraints on various extended cosmologies including massive neutrinos and evolving dark energy. Beyond cosmological results I will present advances in testing for and mitigating potential systematics in these measurements and our theoretical model.

Speaker: Gerrit Farren (Lawrence Berkeley National Laboratory)

5 Tomographic Galaxy Cross-Correlations with tSZ and CIB: A Bias-Robust Probe of Baryons and Cosmology

The cross-correlation of galaxies at different redshifts with other tracers of the large-scale structure can be used to reconstruct the cosmic mean of key physical quantities and their evolution over billions of years, at high precision. In particular, cross-correlating redshift-sliced galaxy samples with thermal Sunyaev–Zel’dovich (tSZ) and cosmic infrared background (CIB) maps enables measurements of the halo bias–weighted electron pressure ⟨bPe⟩ and star-formation rate density ⟨bρSFR⟩ as a function of redshift.

A key obstacle in this program is the dependence of reconstructed quantities on the clustering properties of the galaxy sample. I will present a systematic exploration of tomographic estimators and demonstrate, using the FLAMINGO hydrodynamic simulations, that a bias-independent estimator can be constructed. This estimator is explicitly insensitive to small-scale galaxy bias and remains robust across different galaxy selections. I will show that ⟨bPe⟩ and ⟨bρSFR⟩ can be reconstructed with 1–3% accuracy over a broad redshift range, and that their interpretation is well described by a halo-model framework provided accurate inputs for the halo mass function and large-scale bias are available.

Beyond a single fiducial cosmology, I will also discuss how tomographic tSZ cross-correlations respond to changes in halo abundance and structure growth. By extending the analysis to multiple cosmological models, this framework becomes a controlled laboratory to simultaneously test baryonic physics and cosmology. These results establish tomographic cross-correlations as a precision, bias-robust probe for next-generation surveys.

Speaker: Sara Maleubre (University of Oxford)

6 kSZ velocity reconstruction with ACT DR6 and looking forward to SO

The kinetic Sunyaev--Zel'dovich (kSZ) effect is the dominant small-scale CMB blackbody anisotropy, and is sensitive to the electron density field as well as the large scale velocity field of the Universe. It has recently become possible to measure at high significance over a wide sky area with the Atacama Cosmology Telescope (ACT) data, and will be an even more significant signal in Simons Observatory (SO). In combination with a galaxy survey, we can use this signal to measure directly the velocity field of the high-redshift Universe for the first time through a process known as kSZ velocity reconstruction. One exciting application of this method is primordial non-Gaussianity constraints; the fNL constraints from kSZ velocity reconstruction with SO may be the tightest available.

I will present and discuss the first and most recent kSZ velocity measurements with the ACT DR6 data combined with the DESI Legacy galaxies, whereby we measure the velocity field of our Universe at high significance and use the measurement constrain primordial non-Gaussianity. I will present foreground removal techniques for this measurement, particularly relevant for future measurements with photometric surveys like LSST and Euclid. Finally, I will look to the near future and briefly present forecasts on the constraining power we will have on the non-Gaussianity parameter $f_{NL}$ with Simons Observatory

Speaker: Fiona McCarthy

12:00 Questions

12:30 Lunch break

Dark energy and modified gravity

7 Gravity in the Era of Stage IV LSS Surveys

Stage IV Large Scale Structure Surveys are ushering in a new era of precision cosmology!
In this talk, I will explore the effort to test gravity on cosmological scales, highlighting the theoretical advancements aimed at constructing an optimal framework. I will also touch on the synergy with gravitational wave surveys. Additionally, I will provide a detailed review of recent findings based on currently available data and conclude with an outlook on the challenges and future prospects in this field.

Speaker: Alessandra Silvestri

Flash talks and Poster session I

16:00 Coffee break

Dark energy and modified gravity

8 Constraining dark sector models with galaxy clustering and the CMB

In several cosmological scenarios, such as massive neutrinos or ultra-light axions, the dark matter comprises a warm component alongside the cold one. This modifies the late-time evolution of the dark sector, thus making galaxy clustering an ideal probe of these models. We study the non-linear evolution of perturbations in this context, and build an EFTofLSS-based model that allows for a full-shape fit of the galaxy power spectrum. I will present applications to real data, featuring CMB, CMB lensing and spectroscopic clustering from BOSS and DESI, showing how this can be used to consistently constrain ultra-light axions. I will also present some recent developments on higher-order correlation functions for projected clustering to constrain $\Lambda$CDM parameters.

Speakers: Francesco Verdiani (SISSA, Trieste), Francesco Verdiani (SISSA, Trieste)

9 Microphysics of Dynamical Dark Energy

Hints of dynamical dark energy have recently emerged from distance measurements from type Ia supernovae and galaxies through the Baryonic Acoustic Oscillation feature, challenging the current paradigm in cosmology. This new perspective has encouraged the proposal of physical mechanisms able to consistently explain the observations, such as modified gravity and interactions between dark matter and dark energy. While the equation of state is an important property of dark energy, in order to understand its nature and distinguish different candidate models, we must probe its other characteristics. One such quantity is the sound speed, which dictates the evolution of dark energy inhomogeneities and can affect the formation of the large-scale structure of the Universe. In standard analyses, the sound speed is assumed to be equal to one, which suppresses dark energy perturbations inside the horizon. In this talk, I explore the consequences of a non-standard dark energy sound speed, both within General Relativity and in Modified Gravity theories. In particular, I show that Modified Gravity can make a phantom equation of state physically viable and absent of instabilities. When analyzing data from CMB, BAO, supernovae, and cosmic shear, we observe hints for deviations from General Relativity. This work ties dynamical dark energy with modified gravity, two extensions to $\Lambda$CDM that can work together to provide a consistent picture of the Universe.

Speaker: João Victor Silva Rebouças

10 The distribution and nature of dark matter

We combine ESA's Euclid mission and NASA's SuperBIT mission to test the hypothesis that dark matter particles interact with each other, through forces besides gravity. The hypothesis predicts that dark matter’s trajectory through collisions will deviate from the purely gravitational trajectories followed by stars. To test it, we have observed astrophysical versions of dark matter colliders like the Bullet cluster. We compare the location and amount of dark matter (gravitational lensing) with that of stars (optical imaging) and gas (X-ray imaging). Observations are interpreted and calibrated against cosmological simulations that include both beyond-standard model dark matter physics and hydrodynamical processes of galaxy formation.

Speaker: Richard Massey (Durham University)

11 A New Public Framework for Testing Gravity with Full-Shape Galaxy Clustering

Signatures from departures away from the standard model of cosmology justify the search for extended models of gravity. The full shape data from DESI DR2 will provide enhanced precision to test the growth of structure, valuable to constraints extensions beyond the standard model of gravity. We develop a new EFT pipeline for phenomenological tests of gravity, providing a framework for constraining modifications of gravity using full-shape of galaxy clustering. The code implements a 1-loop correction method particularly sensitive to scale-dependent modifications in the growth of structure for both power spectrum and bispectrum, while retaining a high-speed that is suitable for state-of-the-art Stage-IV surveys, including both phenomenological approaches and the Horndeski effective field theory basis.

We perform extensive validation of the analysis pipeline against realistic galaxy mock catalogues in both ΛCDM and modified gravity scenarios, demonstrating its ability to recover unbiased cosmological parameters across a wide range of models while dealing with projection effects. These improvements establish a robust and accurate methodology for testing gravity with spectroscopic large-scale structure data.

Speakers: Cristhian Garcia Quintero (Center for Astrophysics Harvard-Smithsonian), Rafaela Gsponer (EPFL)

12 What drives a high growth index? Insights from dark energy and varying G.

Recent observational determinations of the cosmological growth index suggest values significantly higher than the standard ΛCDM prediction. I will discuss whether two cosmological scenarios can account for such high values. First, I will show that both homogeneous and clustering dark energy models face serious difficulties in producing elevated growth index values (arXiv:2411.00963). Next, I will show that varying-G parametrizations can yield such high values, implying a 2.4σ–3.4σ tension with the constant-G hypothesis, depending on the parametrization (arXiv:2510.15054). I will also address preliminary determinations of the growth index in the w₀wₐ parametrization using more recent cosmological data.

Speaker: Ronaldo Batista (Federal University of Rio Grande do Norte)

13 Non-linear matter power spectrum for interacting dark sector models

Interacting dark sector (IDS) models provide a commonly explored extension of the standard $\Lambda$CDM cosmology, allowing for non-gravitational energy--momentum exchange between cold dark matter (CDM) and dark energy (DE). Although such models can reproduce similar background expansion history as dynamical DE models, their impact on the growth of cosmic structures is fundamentally different and requires a careful treatment of cosmological perturbations. In this work, we develop the one-loop Standard Perturbation Theory (SPT) formalism for IDS cosmologies without invoking the Einstein--de~Sitter (EdS) approximation. We show that even weak dark sector interactions induce a non-trivial time dependence in the perturbative kernels, leading to a breakdown of the EdS approximation commonly assumed in $\Lambda$CDM analyses. By deriving and numerically solving the evolution equations for the second- and third-order kernels, we compute the corresponding one-loop corrections to the matter power spectrum and find that the resulting deviations can significantly exceed the percent level, even for small interaction strengths. Our results demonstrate that nonlinear corrections are systematically enhanced in IDS models and that neglecting the full time dependence of the kernels can lead to biased predictions on mildly nonlinear scales. We also propose a separable time-dependent solution for the non-linear kernels that agree with the full solution in about 1%. These findings establish the necessity of a time-dependent perturbative treatment for IDS scenarios and provide a robust framework for precision tests using nonlinear large-scale structure (LSS) observables.

Speaker: Rodrigo von Marttens (Federal University of Bahia)

18:00 Questions

Wednesday 9 September

Baryonic Physics & Feedback I

14 Bit by Bit: Building Galaxy Cluster Simulations for Euclid

Galaxy clusters are the most massive gravitationally bound objects in the Universe, and their abundance and spatial distribution make them powerful probes of cosmology. Extracting this information from upcoming surveys such as Euclid, however, requires theoretical predictions that are accurate enough to match the quality of the data. In this seminar, I will present recent work within the Euclid Collaboration aimed at improving three key ingredients of cluster cosmology: the halo mass function, which predicts the abundance of clusters as a function of mass; the halo bias, which describes how clusters trace the underlying matter distribution; and the impact of baryonic feedback, which can shift cluster masses away from the dark-matter-only expectation.

Speaker: Tiago Batalha de Castro (USP)

15 Alexandra Amon: Impact of Baryons for WL

Speaker: Alex Amon

10:30 Coffee break

16 Towards robust cross-correlations of LSS with X-ray observations

Diffuse X-ray emission from hot intracluster gas and emission from active galactic nuclei (AGN) provide complementary tracers of large-scale structure, encoding rich information about baryonic feedback, black hole and galaxy formation, and cosmology. These observables are particularly promising for cross-correlation studies with upcoming wide-field X-ray surveys.

We present a simulation-based framework to model a suite of X-ray observables. First, we introduce a baryonification-based model for stacked X-ray surface brightness profiles. Applying this model to XMM-Newton CHEX-MATE clusters and eROSITA eFEDS groups, we obtain consistent fits across multiple mass and redshift bins and derive constraints on the strength of baryonic feedback. We then extend this framework to generate diffuse X-ray emission maps from baryonified $N$-body lightcones.

Finally, we introduce a simulation-based model for X-ray AGN emission based on subhalo abundance matching. Together, these components provide a promising basis for forward-modelling and cross-correlation analyses of upcoming wide-field X-ray surveys such as eROSITA.

Speaker: Jozef Bucko (ETH Zurich)

17 Baryonified Lightcones: A Unified Framework for LSS–CMB Cross‑Correlation Cosmology

Understanding the impact of baryonic feedback on the matter distribution is a major challenge for precision cosmology, especially for analyses combining large-scale structure tracers with CMB secondary anisotropies. We recently showed that combining kinematic Sunyaev–Zel’dovich measurements from ACT with gas‑fraction data from eROSITA provides strong constraints on gas thermodynamics in massive halos, with the BFC baryonification framework favoring strong‑feedback models consistent with FLAMINGO.

In the first part of this talk, I will summarize these results and illustrate how combining CMB and X‑ray observables constrains baryonic feedback.

In the second part, I will present our extension of the baryonification framework to full cosmological lightcones. Starting from dark‑matter‑only shells from the CosmoGrid simulation suite, we apply the updated BFC displacement model to generate self‑consistent gas, stellar, and dark‑matter fields, enabling forward‑modeling of multiple observables within a unified framework.

I will then show first results, including high‑resolution thermal and kinematic SZ maps on the HEALPix grid. This approach provides an efficient path from dark‑matter‑only simulations to realistic CMB secondary anisotropies and supports consistent modeling of correlations between LSS tracers and CMB signals.

Finally, I will discuss validation against FLAMINGO and extensions to additional probes such as X‑ray emission and weak‑lensing shear. By jointly modeling LSS tracers with tSZ and kSZ effects, this framework enables unified multi‑probe analyses that constrain both cosmology and baryonic feedback.

Speaker: Michael Kovac (University of Manchester)

18 Toward a consensus picture of baryon feedback: Joint X-ray, Sunyaev-Zeldovich, and weak lensing measurements

There is no consensus on how baryon feedback shapes the underlying matter distribution from either simulations or observations. We confront the uncertain landscape by jointly analyzing the kinetic and thermal Sunyaev-Zel’dovich (kSZ) effects and X-ray gas mass fractions, each characterized with galaxy-galaxy lensing. Across group and clusters masses and between $0<z<1$, we find consistent evidence of more efficient gas expulsion beyond the virial radius than predicted by most state-of-the-art simulations, implying significant suppression of the matter power spectrum on small scales. We incorporate these constraints into data-driven priors for cosmic shear, significantly improving cosmological constraining power on small scales. By jointly constraining the halos’ gas density, gas pressure, and total matter profiles, we are investigating the physical mechanism behind this gas expulsion.

Speaker: Jared Siegel Siegel (Princeton University)

19 A robust view of feedback in the TNG model

We present a new analysis of the IllustrisTNG galaxy formation model based on a set of simultaneous multi-zoom hydrodynamical simulations of halos embedded within a common cosmological volume. This framework allows us to efficiently probe galaxy populations across a wide range of masses and environments while maintaining full cosmological context. We compare predictions for the galaxy stellar mass function and gas fractions in groups and clusters to current observational measurements, using Gaussian-process emulation to explore model variations at low computational cost. Our results quantify where IllustrisTNG provides a robust description of galaxy populations and identify regimes in which tensions with the data reveal limitations of the model-assumptions.

Speaker: Francisco Germano Maion

12:00 Questions

12:30 Lunch break

SBI and Field level inference

20 Fabian Schmidt: Simulations and IA for future analyses

Speaker: Fabian Schmidt

21 Simulation-based inference for multi-probe cosmology

Cosmology is entering an era in which inference can be performed directly from maps and fields, using simulation-based inference (SBI) across both large-scale structure and CMB surveys, offering a way to trace the underlying rhythms of the cosmos across multiple probes and scales.

I will begin by motivating field-level inference as a powerful approach to extracting cosmological information from cosmic structure and reconstructing the initial conditions of the Universe. I will present and benchmark a range of field-level methods, from differentiable forward modeling to machine-learning approaches, and show the significant gains they deliver for DESI BAO. I will then present an SBI pipeline for large-scale CMB B modes in current ground-based experiments, showing how combining Needlet-ILC with neural posterior estimation allows us to marginalize over complex Galactic foregrounds while improving constraints on the tensor-to-scalar ratio, r.

I will conclude by presenting methods to make SBI robust, interpretable, and efficient, and by outlining its broader role in next-generation cosmology, including simulations being developed within the Simons Observatory ecosystem to enable SBI for multi-probe cross-correlations.

Speaker: Adrian E. Bayer Not Supplied (Flatiron Institute / Princeton University)

22 Fast tools for multi-probe forward modelling

Simulation-based inference is going to be play a key role in the upcoming cosmological analyses. For this reason, I will present an end-to-end pipeline designed for multi-probe simulation-based inference.

I first present CosmoGridV1, a suite of lightcone simulations for map-level cosmological inference. The simulation suite spans the wCDM model and includes a fiducial cosmology with 200 independent realisations and a benchmark set with larger boxes, higher particle counts and higher redshift resolution of shells.

I will then discuss Ufalcon, a post-processing tool that generates multi-probe maps from simulations for a range of cosmological probes, including galaxy overdensity, weak-lensing convergence, CMB lensing, and the integrated Sachs-Wolfe (ISW) temperature perturbation.

Finally, I will introduce SwiftCl (Reymond et al, 2026), a fast and differentiable tool for computing angular power spectra beyond the Limber approximation. This tool enables multi-probe analysis for galaxy clustering, weak lensing, CMB lensing, and CMB ISW. Together, these tools provide an complete framework for next-generation cosmological constraints.

Speaker: Laura Reymond (ETH Zürich)

23 Deep learning insights into non-universality in the halo mass function

The abundance of dark matter halos is a key cosmological probe in forthcoming surveys. Placing tight constraints requires modelling the halo mass function to at least percent-level accuracy over a wide cosmological parameter space. However, a theoretical understanding of what is required for such accurate modelling is incomplete, limiting the generalisability of existing halo mass function models. We present a novel approach to gain this understanding using deep learning. Unlike existing approaches, it requires minimal assumptions on the relevant physical quantities or their parametrisations. Instead, the deep-learning model compresses all the relevant quantities into a latent representation, which we interpret using mutual information. We find our model requires only three latent variables to reproduce the halo mass functions from the state-of-the-art Aemulus emulator at $z=0$ to within 0.25% residuals over $M = 10^{13.2-15} \mathit{h}^{-1} M_\odot$ in a $w$CDM$+N_\mathrm{eff}$ parameter space. Interpreting the latent representation, we find that in addition to information expected from the extended Press-Schechter formalism, it also captures non-universality (information beyond mass variance) that is required for accurately modelling cosmology dependence. We find this additional information is strongly correlated with the recent growth history since dark energy domination, which can be parametrised by the linear growth rate at $z\sim 0.05$ for lower mass halos in our mass range, and by $\Omega_m$ for our highest mass halos. Non-universality additionally depends on the effective neutrino number $N_\mathrm{eff}$. The compact representation our model learnt can also inform the design of emulator training sets to achieve high emulator accuracy with fewer simulations.

Speaker: Ningyuan (Lillian) Guo (Royal Holloway, University of London)

24 How much cosmology is encoded in galaxies?

Galaxies are the primary tracers of the large-scale structure of the Universe and are traditionally used through summary statistics such as correlation functions and power spectra to constrain cosmological models. However, galaxies themselves are complex systems whose spatial distribution, internal properties, and environments may encode additional cosmological information beyond these traditional summaries. In this talk, I explore how modern machine learning techniques can help uncover this information directly from galaxy populations. I will present recent work using graph neural networks (GNNs) to infer cosmological parameters from galaxy catalogs, studies investigating the cosmological information content of individual galaxies, and ongoing efforts to extract reliable galaxy properties such as redshift from imaging and photometric data. Together, these approaches suggest new ways to connect galaxies and cosmology, potentially expanding the information accessible in the era of precision large-scale structure surveys.

Speaker: Mrs Natalí Soler Matubaro de Santi

15:30 Questions

16:00 Coffee break

25 Baojiu Li: Numerical simulations for LSS x CMB analysis

Speaker: Baojiu Li

26 Emulator development efforts within Euclid

In this talk I will present an overview of current cosmological emulator development efforts in Euclid, aimed at enabling efficient and accurate parameter inference in the era of high-precision cosmology. Cosmological emulators are surrogate models trained on high-fidelity theoretical predictions from Boltzmann solvers, or from numerical simulations. Once trained, these models can reproduce complex observables with percent-level accuracy while reducing the computational cost of evaluation by several orders of magnitude. A single emulator prediction can be produced in milliseconds rather than minutes, making these tools essential for modern Bayesian inference methods, which require millions of model evaluations across high-dimensional cosmological parameter spaces.

I will focus in particular on CosmoPower emulators designed to predict both large-scale structure and cosmic microwave background observables in multi-probe cosmological analyses. For large-scale structure, this includes emulators of the linear and nonlinear matter power spectrum used in combined analyses of cosmic shear, galaxy clustering, and galaxy–galaxy lensing. At the linear level, accurate emulation requires reproducing the transfer function and growth history across a wide cosmological parameter space, while at nonlinear scales additional complexity arises from gravitational collapse and baryonic feedback processes.

I will also present recent work on CMB power spectrum emulators, which provide fast predictions for temperature and polarization spectra and enable efficient joint analyses combining CMB and large-scale structure probes. Finally, I will discuss ongoing efforts to extend emulator coverage beyond the standard ΛCDM models, with emphasis on training strategies, validation, and the propagation of emulator uncertainties into cosmological constraints.

Speaker: Ivan Sladoljev (Royal Holloway)

27 Forward-Modelling Galaxy Surveys: A Robust Analytic Model for Projected Galaxy Bias

How can we accurately test extensions to ΛCDM when unmodelled baryonic dynamics obscure the galaxy-halo connection? While galaxies are vital tracers of large-scale structure, residual uncertainties in their distribution often obstruct cosmological inference, especially in two-dimensional projections where halo-level information is incomplete. I present an analytic galaxy bias model in projection that incorporates stochasticity and non-locality at linear order while enforcing physical consistency.
By calibrating the model to hydrodynamical simulations, I demonstrate that it matches two-point statistics down to the simulation resolution and recovers the bispectrum down to 10 Mpc up to z=3. The model outperforms standard local bias approaches by capturing non-linearities driven by mode coupling and phase correlations across a wide range of halo masses. This framework improves the robustness of joint clustering and galaxy-galaxy lensing tests, allowing one to successfully separate astrophysical systematics from genuine scale-dependent structure growth. Finally, this model enables efficient field-level forward modelling of galaxy positions, providing a principled and practical route for simulation-based inference with upcoming surveys like Euclid and Rubin LSST.

Speaker: Maximilian von Wietersheim-Kramsta (Durham University)

28 Simulation-based emulators for DESI galaxy clustering

I will present a pipeline to emulate galaxy clustering statistics at the two-point level and beyond, down to the non-linear regime, including many alternative summary statistics for which no complete analytic models exist in the literature, including the wavelet scattering transform, density-split clustering, Minkowski functionals, void statistics, and more. Our theory models are based on neural networks trained on high-fidelity N-body simulations that meet the requirements to reproduce the properties of the luminous red galaxy sample from the Dark Energy Spectroscopic Instrument. We test the performance of our pipeline at recovering cosmological parameters within the context of the LCDM model and its extensions, and validate its applicability beyond the halo occupation distribution framework that is used to model the connection between dark matter halos and galaxies. We combine the bits of each summary statistic that maximize the Fisher information into a single data vector through a greedy algorithm, which achieves the tightest cosmological constraining power in all cases that are studied.

Speaker: Enrique Paillas (University of Arizona)

29 Field Level Inference: Bayesian Hierarchical Models for Next-Generation Large-Scale Structure Analysis

Field-level inference – the direct statistical reconstruction of cosmological fields from observational data – is emerging as a transformative paradigm for next-generation galaxy surveys like Euclid, LSST, and DESI. Unlike traditional summary statistics, this approach infers latent fields (e.g. matter density, weak-lensing, cmb convergence) and their uncertainties directly, leveraging the full information content of the data to break degeneracies in cosmological parameters.

In this talk, I contrast two Bayesian frameworks enabling this paradigm: Almanac, a hierarchical method for joint reconstruction of full-sky fields and their power spectra from masked, noisy data; and BORG, which uses physics-based priors from structure formation to infer the initial conditions of the Universe. Applied to the Quaia quasar sample, we validate the BORG field-level reconstruction through cross-correlations with CMB lensing. Building on Almanac, I also present FLINCH, an extension that propagates field-level inference to cosmological parameter space; applied to CMB simulations, it improves cosmological constraints by up to 40% compared to conventional summary-statistic analyses. Together, these advances demonstrate how scalable Bayesian frameworks can unify data and theory, maximising the scientific return of the upcoming new era of cosmic surveys.

Speaker: Dr Arthur Loureiro (Stockholm University)

18:00 Questions

Thursday 10 September

Large scale sctructure I

30 Luca Amendola: 6 × 2pt method: supernova velocities meet multiple tracers

Speaker: Luca Amendola (University of Heidelberg)

31 Henrique Rubira: Novel results in perturbation theory for LSS

Speaker: Henrique Rubira (LMU/Cambridge)

32 Growth rate measurement with DESI DR1 peculiar velocities

Peculiar velocities are a great probe of gravity allowing us to test the validity of general relativity on cosmic scales. I will describe the latest measurement of the growth rate of structures at redshift z = 0.07 using a combination of galaxy positions and direct peculiar velocities from the DESI Peculiar Velocity survey. Our measurements significantly contribute to constraining cosmological parameters encoding deviations from GR, such as the growth index.

Speaker: Julian Bautista (Aix-Marseille Univ - CPPM)

10:30 Coffee break

Primordial non-Gaussianity

33 SPHEREx Overview and Status

SPHEREx, a satellite in NASA’s Medium Explorer program, was launched in March 2025 and is currently conducting the first all-sky near infrared spectral survey from 0.75 to 5 microns. Using linear variable filters mounted on six H2RG detector arrays, SPHEREx obtains low resolution spectra across the entire sky in 102 spectral channels with a resolving power of about 35 to 130. The mission is designed to address three primary science goals: probing the physics of cosmic inflation through large scale structure, tracing the origin of water and biogenic molecules in the form of interstellar ices, and studying the formation and evolution of galaxies across cosmic time. During its nominal mission SPHEREx will produce four full sky spectral maps that together form a unique legacy archive for the astronomical community. The survey will include spectra for hundreds of millions of galaxies and stars and a large sample of ice absorption measurements in the interstellar medium. This talk will provide a general overview of the SPHEREx mission and current survey status, and will highlight early analysis efforts including progress toward measurements of the extragalactic background light and other emerging science results.

Speaker: Howard Hui (Caltech)

34 The SPHEREx All-Sky Galaxy Catalog: Probing Primordial Non-Gaussianity and Synergy Opportunities

SPHEREx is a near-infrared satellite mission launched in March 2025, currently conducting the first all-sky near-infrared spectral survey. Its primary cosmological objective is to constrain primordial non-Gaussianity through 3D galaxy clustering, using the all-sky galaxy catalog built from SPHEREx high-resolution photometric spectra. This talk will begin with an overview of the SPHEREx cosmology analysis, with emphasis on preliminary efforts to construct and validate the SPHEREx redshift catalog and to optimize the multi-tracer analysis for primordial non-Gaussianity constraints. I will conclude by discussing potential synergies between the SPHEREx galaxy catalog and a range of current and upcoming CMB and LSS surveys.

Speaker: Yun Ting Cheng

35 Colliders in the Sky: Constraining High-Energy Physics with CMB and LSS Observations

Inflation is amongst the most mysterious phenomena in physics. With an energy scale potentially reaching 10^13 TeV, its physical description likely lies far beyond the realm of the standard model. This leaves many questions unanswered: what fields were present during inflation? how did they interact with each other? In this talk, I will discuss how modern cosmological datasets can be used to shed light on the early Universe by searching for the tell-tale signs of “primordial non-Gaussianity”. In particular, I will present new searches for inflationary signals in Cosmic Microwave Background and Galaxy Survey data, which allow for a detailed study of the primordial three- and four-point functions. Leveraging an array of theoretical and computational tricks, these methods can place constraints on the microphysics of inflation and directly probe particle scattering processes in the early Universe, acting as a “cosmological collider”. I will close by discussing future avenues of exploration and prospects for upcoming galaxy surveys.

Speaker: Oliver Philcox (Stanford University)

36 Primordial non-Gaussianity from LSS and its cross-correlations: status and prospects

Measuring the local primordial non-Gaussianity parameter, fNL, is crucial for understanding the nature of inflation, as it can rule out or confirm the various inflationary models. Although the current best constraint on fNL is achieved by the cosmic microwave background (CMB) bispectrum, datasets from large surveys (DESI, Euclid, LSST) are providing this decade another cosmic window to fundamental physics through the scale-dependent bias effect. The main challenge for performing fNL measurements from LSS are observational systematics, and a way to mitigate their impact is to perform cross-correlations with observables sensitive to different systematics like the CMB lensing. In this presentation, I will review the current status of the fNL measurements from LSS and discuss new methodologies for improving them. In particular, I will highlight the results from Bermejo-Climent et al. (2026), where we measure fNL with an uncertainty about ~14 from the Quaia quasar catalog by using a new observable called 'angular redshift fluctuations', in combination with quasar density and CMB lensing. This methodology improves by ~30% the previous analysis and is currently being applied to DESI and Euclid data.

Speaker: Dr Jose Bermejo (Konkoly Observatory)

37 Primordial non-gaussian bias from the time evolution of tracer number counts

The presence of additional light fields during inflation can be robustly inferred (or ruled out), if signatures of primordial non-Gaussianity (PNG) of the local type are found (or not found) in upcoming cosmological surveys. In fact, upcoming measurements of the distribution of large-scale structures (LSS) in our Universe will have enough sensitivity to reach important theoretical thresholds distinguishing the single and multi-field regimes. This is only possible due to a well-known scale-dependent modulation in the distribution of biased tracers, such as galaxies, in comparison to the underlying matter field. Unfortunately, in this scale-dependent bias effect the amplitude of PNG is exactly degenerate with an unknown PNG bias coefficient, which hence needs to be independently estimated in order to produce a measurement of PNG from LSS observations. In this talk I show how the time evolution of tracer number counts can be used to estimate the PNG bias coefficient, using both N-body and Hydrodynamical simulations of LSS formation. I will argue that observational selection effects of specific surveys can be accounted for, and comment on applying this strategy to existing and upcoming datasets.

Speaker: Caio B. de S. Nascimento (Perimeter Institute)

38 Updates on the Search for Cosmic Topology (COMPACT Collaboration)

The question of whether our universe is finite or infinite remains an open enigma in cosmology. While most studies assume a spatially infinite universe, statistical anomalies in the Cosmic Microwave Background (CMB) and significant methodological limitations in previous analyses call this assumption into question. In this talk, I will present recent findings from the COMPACT collaboration, focusing on the search for cosmic topologies and their potential implications for explaining CMB anomalies.

Speaker: Dr Thiago Pereira (Universidade Estadual de Londrina)

12:30 Questions

Friday 11 September

CMB II

39 Simons Observatory

Speaker: Jo Dunkley

40 Discoveries from CMB-HD

CMB experiments have contributed powerful constraints on the fundamental physics and astrophysics of the Universe. Current CMB experiments, such as the Simons Observatory, are poised to extend this progress even further. However, CMB experiments still have a wealth of information to offer beyond near-term facilities, including probing the properties of dark matter, inflation, and light relic particles. In particular, a much lower-noise and higher-resolution wide-area CMB survey can cross a number of critical fundamental physics thresholds and open a relatively untapped window of small-scale, late-time CMB anisotropies. Here I will discuss CMB-HD, a next-generation CMB facility, as well as the discoveries it can enable.

Speaker: Neelima Sehgal

41 CMB spectral distortions

Speaker: Nabila Aghanim

10:30 Coffee break

42 Precision Cosmology from the Atacama Cosmology Telescope's New CMB Lensing Maps

The gravitational lensing of the Cosmic Microwave Background (CMB) provides a powerful and robust probe of the projected matter distribution across cosmic time, offering unique sensitivity to the growth of large-scale structure, cosmic expansion, and fundamental physics such as the sum of neutrino masses. As cosmology enters a high-precision era, CMB lensing has become a cornerstone observable for testing the standard ΛCDM model and characterizing emerging tensions.
In this talk, I will present results from the final data release of the Atacama Cosmology Telescope (ACT), including state-of-the-art CMB lensing maps covering 30% of the sky. These maps combine improved nighttime and daytime ACT observations with large-scale CMB data from Planck, delivering high-fidelity lensing reconstructions that substantially advance over previous measurements. I will discuss updated constraints on the amplitude of structure growth, neutrino mass upper limits, and other key cosmological parameters derived from these maps, as well as their implications for current cosmological tensions and possible extensions beyond ΛCDM.

Speaker: Frank Qu (Stanford)

43 The high cost of a low optical depth

The past decade has seen the rise of high-precision cosmological observations accompanied by emerging tensions among various datasets when interpreted within the standard cosmological model (ΛCDM). Recently, baryonic acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) have shown a mild discrepancy with current cosmic microwave background (CMB) data. While a time-dependent dark energy component offers a better fit to the combined BAO+CMB dataset, it comes at the high cost of introducing two new phenomenological parameters and has the undesirable feature of exacerbating the Hubble tension. I'll briefly summarize alternative new-physics proposals and primarily focus on a (speculative, but minimal) scenario in which the optical depth to reionization is underestimated. I'll discuss the plausibility of this scenario in light of several recent rebuttals, the current status of an ongoing reanalysis of Planck large-scale polarization, and will conclude with open questions and time for discussion.

Speaker: Noah Sailer (Stanford University)

44 Leveraging simulations to study the millimetre sky

Observations of the millimetre sky contain a wealth of signals from across the history of the Universe. Current observations have reached the sensitivity where we able to make precision measurements of the signals sourced by the large-scale structure of the Universe, known as CMB secondary anisotropies. Optimally analyzing many of these signals is challenging as CMB secondaries are highly non-Gaussian and thus it is challenging to derive sufficient statistics that extract all their astrophysical and cosmological information. In this presentation I will introduce the Backlight program that leverages a set of realistic non-Gaussian mocks of CMB secondaries and correlated signals to develop novel analysis methods.

Speaker: Will Coulton

12:00 Questions

12:30 Lunch break

Large scale sctructure II

Flash talks and Poster session II

16:00 Coffee break

Large scale sctructure II

45 The ESA Euclid mission: from dreams to reality

I shall describe the ESA Euclid mission, from its adoption by ESA in 2011 to its current status. I will provide an overview of its capabilites, scientific goals and the coordinated effort undertaken by the collaboration to deliver the upcoming first Data Release (DR1).

Speaker: Dr Pablo Fosalba (Institute of Space Sciences (ICE-CSIC, IEEC))

46 Cosmology Likelihood for Observables in Euclid

I will provide a description of the code implementation and structure of Cosmology Likelihood for Observables in Euclid (CLOE), developed by members of the Euclid Consortium. CLOE is a modular Python code for computing the theoretical predictions of cosmological observables and evaluating them against state-of-the-art data from galaxy surveys such as Euclid in a unified likelihood. This primarily includes the core observables of weak gravitational lensing, photometric galaxy clustering, galaxy-galaxy lensing, and spectroscopic galaxy clustering, but also extended probes such as the clusters of galaxies and cross-correlations of galaxy positions and shapes with the cosmic microwave background. While CLOE has been developed to serve as the unified framework for the parameter inferences in Euclid, it has general capabilities that can serve the broader cosmological community. It is different from other comparable cosmological tools in that it is written entirely in Python, performs the full likelihood calculation, and includes both photometric and spectroscopic observables. I will focus on the primary probes of Euclid and will describe the overall code structure, unique features, and speed optimization strategies needed to inform us about the underlying nature of the Universe

Speakers: Prof. Shahab Joudaki (CIEMAT, Spain), Shahab Joudaki (CIEMAT)

47 Detecting gravitational wave-galaxy cross-correlations

Gravitational waves (GWs) are emerging as a potentially powerful probe of the Universe on large scales. Notably, they may contribute in the coming years to addressing the Hubble tension, as both the number of observed GW events increases and the capacity of current detectors to localise their sources improves. In this talk, I will discuss a new method for measuring the Hubble constant using GWs, based on their 3D cross-correlations with galaxies—known as Peak Sirens. I will present our recent work where we detected for the first time those cross-correlations, at 5.9$\sigma$, with the GWTC-3 and GLADE+ catalogs. We obtained the first measurement of the Hubble constant from this method, and the first bounds whatsoever on the gravitational wave clustering bias. This work opens a new window for analysing GW sources as tracers of the large scale structures.

Speaker: Isabela Santiago de Matos (University of Portsmouth)

48 Cosmology with LVK Dark Sirens and Euclid latest catalogs available

We present a study aimed at using the galaxy catalog released by Euclid for Gravitational-wave (GW) cosmology. I will firstly present an overview of the galaxy catalogs released and planned to be released with Euclid, focusing on their overlap with current GW detections. We identified six candidate events with significant spatial overlap with Euclid. I then focus on presenting the characterization of the luminosity function and completeness of galaxies in Euclid Data Release 1 (DR1) and explain how these key studies are at the base of the dark siren method for GW cosmology. Our results represent an initial step toward establishing Euclid as a key resource for dark siren analyses in gravitational-wave cosmology.

Speaker: Sarah FERRAIUOLO (AMY&Sapienza)

49 Cosmological and astrophysical aspects of 21 cm intensity mapping surveys

Intensity mapping (IM) of the redshifted 21 cm line emission from neutral hydrogen is an efficient technique for surveying the large-scale structure of the Universe. In this talk, I discuss cosmological and astrophysical aspects of 21 cm IM, addressing instrumental limitations that affect clustering measurements, the role of cross-correlations between radio and photometric galaxy surveys, and the extraction of cosmological constraints from summary statistics through machine learning. These topics are explored in the context of current and upcoming radio telescopes, illustrating how 21 cm IM can contribute to testing fundamental assumptions of the standard cosmological model and constraining its parameters.

Speaker: Camila Novaes (Instituto Nacional de Pesquisas Espaciais)

18:00 Questions

Saturday 12 September

Large scale sctructure III

50 Environmental dependent clustering in modified gravity simulations

I'll showcase the study of environment-dependent clustering using the marked correlation function applied to Hu-Sawicki $f(R)$ modified gravity simulations. This gravity theory enriches the structure formation by enhancing gravity in a scale-dependent form. By employing a multi-scale cosmic structure finder algorithm, we define the cosmic environments divided in: nodes, filaments, walls and voids. We find a stronger impact of modified gravity in nodes and filament, which together dominate the information content by more than a factor of four relative to other environments. Combining environmental information further enhances the expected signal-to-noise ratio for CMASS- and DESI-like mock samples, particularly in configurations including filaments. Overall, marked correlation functions that incorporate environmental structure increase the information content by about a factor of two compared to standard density-based marks applied to the full galaxy sample. These results demonstrate the importance of environmental information, especially from filaments, in improving the constraining power of galaxy clustering tests of modified gravity.

Speaker: Joaquin Armijo (IFUSP)

51 Cosmology with Galaxys and Quasars in narrow-band large-sky surveys

This talk presents a research project centered on the construction and scientific exploitation of the galaxy and quasar catalogs in J-PAS and S-PLUS surveys. Building upon expertise developed within the S-PLUS survey, this project utilizes Machine Learning (ML) techniques - such as Bayesian Neural Networks, FlexCoDE, and foundation models - to enhance classification and photometric redshift estimation of galaxies and quasars by combining narrow-band and broad-band filters with near-infrared data. A central component of the research involves developing and validating new ML tools. We will present an analysis to identify systematics, compute galaxy and quasar bias, allowing us to use the large-scale structure traced by these objects to place constraints on cosmological parameters.

Speakers: Dr Lilianne Nakazono (ON, Brazil), Lilianne Nakazono (ON/MCTI)

52 Detection of cosmological dipoles aligned with transverse velocities

On large scales, peculiar velocities encode a wealth of cosmological information. While line-of-sight components are routinely probed through redshift-space distortions and the kinetic Sunyaev–Zel’dovich effect, measuring transverse velocities has remained challenging. I will present a detection of dipolar patterns on angular scales of tens of degrees imprinted on the Cosmic Microwave Background through the integrated Sachs–Wolfe effect and gravitational lensing. These dipoles are aligned with large-scale transverse velocities and therefore provide a handle to extract cosmological information from them. I will discuss how such measurements can be used to constrain cosmological parameters and test general relativity.

Speaker: Yan-Chuan Cai (University of Edinburgh)

53 UltraLevin: A NumCosmo Algorithm for Efficient Non-Limber Angular Power Spectrum Computation

Two-point correlation functions are among the most powerful probes of cosmology. Additional information is obtained from cross-correlations, which help mitigate systematic effects and break parameter degeneracies. Their numerical evaluation, however, is computationally demanding because it requires multi-dimensional integrations of highly oscillatory functions involving probe kernels and spherical Bessel functions.

The Limber approximation is commonly used to simplify these calculations, but its range of validity becomes limited for the accuracy and angular scales targeted by upcoming surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) and the Euclid mission.

In this work we introduce UltraLevin, a Levin-type algorithm for oscillatory cosmological integrals that combines a reformulation of the Bessel integrals with a spectral ODE solver based on ultraspherical polynomials. The algorithm is designed to evaluate batches of multipoles simultaneously and to automatically identify the effective support of the probe kernels, reducing the computational cost of the integrations.

We validate the approach and compare its numerical accuracy and computational performance with existing implementations, including the non-Limber angular power spectrum calculation available in the Core Cosmology Library (CCL). We also identify the regimes where the Limber approximation remains valid for galaxy clustering, CMB lensing, and galaxy weak lensing.

The method is implemented in the Numerical Cosmology Library (NumCosmo), providing an efficient tool for precision cosmology analyses.

Speaker: Sandro Dias Pinto Vitenti (Universidade Estadual de Londrina)

10:00 Questions

10:30 Coffee break

Baryonic Physics & Feedback II

54 Calibration of baryonic effects using joint modeling of weak lensing, Sunyaev-Zel'dovich effects and galaxies

Future weak lensing surveys are poised to deliver unprecedented cosmological constraints, but their statistical power on small scales is fundamentally limited by systematic uncertainties in baryonic feedback. This feedback alters the total matter power spectrum in a way that is degenerate with key cosmological parameters. We introduce a self-consistent halo model that leverages the kinetic Sunyaev-Zel'dovich (kSZ) effect to directly calibrate baryonic physics. kSZ tomography provides a measurement of the galaxy-electron power spectrum, $P_{ge}$, which is a direct probe of the feedback-induced redistribution of the electron distribution in and around halos. We construct a unified framework that combines a stellar mass-based Halo Occupation Distribution (HOD) model for the galaxy-halo connection, a ``baryonification'' scheme for the distribution of gas and dark matter, and a consistent derivation of thermodynamic observables. We forecast how an upcoming measurement of $P_{ge}$ can be used as a prior to break degeneracies within this model. We forecast that this kSZ calibration as well as tSZ cross-correlation statistics significantly improves constraints on baryonic feedback parameters, allowing for the robust inclusion of small-scale weak lensing and galaxy-galaxy lensing data. This, in turn, sharpens cosmological constraints on parameters like $S_8$ and $\Omega_m$, effectively recovering the information that would otherwise be lost to systematic uncertainty.

Speaker: Shivam Pandey (University of Arizona)

55 The impact and interplay of analysis choices in upcoming cosmic shear studies

Achieving robust cosmological constraints from cosmic shear involves several stages and many different analysis choices. Recent galaxy weak lensing analyses (DES & KiDS 2023) have shown that small shifts in parameter constraints are exacerbated by some combinations of analysis choices. As constraining power from cosmic shear improves, more complex modelling and accounting of systematics is required. Galaxy lensing is affected by baryonic feedback, primarily through active galactic nuclei redistributing matter at the centre of galaxies, when measuring small scales. We have performed a full mock-Rubin cosmic shear analysis and have found that removing data that is strongly affected by baryonic feedback would mean excluding almost 80% of the data, however marginalising over baryonic feedback parameters without any external information leads to minimal improvements in constraining power. This is because data from the Rubin Observatory is so precise that even a small effect is detectable. For baryon systematics we are currently dependent on cosmological hydrodynamical simulations, however cross-correlations with external probes such as X-ray or CMB measurements provide a more direct way to constrain baryons. We will present results on the potential impact of baryons on cosmic shear with Rubin Observatory and the interplay between baryons and other cosmic shear systematics.

Speaker: Naomi Robertson (University of Edinburgh)

56 Constraining baryonic physics in shear analyses using the kSZ power spectrum

The traditional, real-space stacking estimator for the kinematic Sunyaev Zeldovich (kSZ) effect can be expressed as a simple angular power spectrum of two quantities: the CMB temperature field, and the galaxy momentum field. This power spectrum approach is mathematically equivalent to the stacking estimator, and comes with a number of advantages: it is fast to compute, easily connected to Fourier-space theory predictions, and its covariance is straightforward to compute -- without having to rely on simulations or empirical methods. Taking advantage of the already existing power spectrum infrastructure, it is also incredibly easy to seamlessly combine this kSZ measurement into any power spectra analyses: consistent scales cuts can be applied to the measurements, and the covariance of any pair of power spectra can be easily derived from the data.

Introducing the kSZ into analysis pipelines is especially useful to self-calibrate baryonic effects. The kSZ effect is sensitive to the baryonic physics on the line of sight -- namely, the electron density -- and therefore can provide a better handle on nuisance parameters introduced when modelling baryonic effects in LSS analyses. I will show results from a cosmic shear analysis on the DESI photometric Luminous Red Galaxies sample, which also includes the corresponding kSZ measurement.

Speaker: Lea Harscouet (Oxford University)

57 Mass dependence of halo baryon fractions from the kinetic Sunyaev-Zeldovich effect

We detect the kinetic Sunyaev-Zeldovich imprint of peculiar motions of galaxy groups and clusters, using the photometric DESI Legacy Survey together with cosmic microwave background (CMB) maps from the Atacama Cosmology Telescope (ACT). We develop a comprehensive forward model based on the AbacusSummit cosmological simulations: mock galaxy group catalogues and synthetic kSZ maps are generated, together with a reconstructed peculiar velocity field that allows for photo-$z$ errors, redshift-space distortions, and survey masks. We investigate possible contamination from the cosmic infrared background (CIB), finding that CIB effects are subdominant to the kSZ signal in the relevant ACT frequency channel. We then predict the kSZ signal expected when stacking CMB temperature maps around groups, taking account of their estimated radial velocities. Comparing the model with observations, we are able to constrain the total baryon fraction within haloes, as well as their internal gas profiles. We find evidence for mass dependence of the halo baryon fraction within the virial radius. The gas fraction in massive groups is consistent with the universal baryon fraction, but low-mass groups ($10^{12.5} \lesssim M\, /\, \mathrm{M}_\odot \lesssim 10^{14}$) are depleted to $0.38 \pm 0.11$ times the universal baryon fraction. We find this low virial baryon fraction to be consistent with an extended gas profile, for which the total baryon content reaches the universal value well beyond the virial radius. This conclusion is consistent with previous analyses using X-ray, kSZ, and weak lensing, and plausibly reflects energetic feedback processes from the galaxies in these haloes.

Speaker: Finn Roper (University of Edinburgh)

12:00 Questions

12:30 Lunch break

Large scale sctructure III

58 Intrinsic Alignments Around Cosmic Voids: Insights from the Euclid Flagship Simulation

In this talk, I will present a measurement of the intrinsic alignment (IA) signal of galaxies around cosmic voids using the Euclid-like Flagship simulation from the Euclid Collaboration. While IA has been extensively studied in overdense environments, its behaviour in underdense regions remains largely unexplored and may represent a systematic for future void–lensing analyses. We analyse red and blue galaxy populations separately and compare the signal with predictions from the linear alignment model. The redshift evolution of the IA amplitude is consistent with that of the general galaxy population. Our modelling also provides an estimate of the void bias which increases with redshift as expected.

Speaker: Pauline VIELZEUF (cppm)

59 The shape of emptiness: improving the signal from cosmic voids using reconstruction

Cosmic voids, the vast, underdense regions of the Universe, are emerging as powerful cosmological laboratories. Far from being empty, they carry unique imprints of the growth of structure and the underlying physics driving cosmic acceleration. Among the most promising observables in this context is the void-galaxy cross-correlation function, which encodes both the geometry and dynamics of the cosmic web. In this talk, I will explore how the shape of voids can serve as a sensitive probe of cosmology, offering complementary constraints to traditional large-scale structure measurements. I will present recent developments demonstrating how void shapes respond to different cosmological models, and how systematic effects, particularly those related to redshift-space distortions, can be mitigated through advanced velocity reconstruction techniques.

These results highlight the growing potential of void-based analyses in the era of Stage IV spectroscopic surveys, such as Euclid, DESI and Roman, where they will play a crucial role in refining our understanding of gravity and dark energy.

Speaker: Giulia DEGNI (CPPM - AMU)

60 How to measure cosmology from nothing: void-galaxy cross-correlation with DESI

Cosmic voids provide a novel probe of structure formation and cosmic expansion. They are sensitive to structure growth, dark energy, modified gravity, and sum of neutrino masses. Using the DESI spectroscopic data, we perform void identification and present the preliminary measurements of the void-galaxy cross-correlation function. By measuring the void-galaxy cross correlation function we can extract constraints on the content of the Universe and the growth rate of structures through the Alcock Paczynski test and by modeling redshift space distortions. The work I will present highlights the potential of cosmic voids for testing cosmological models with DESI.

Speaker: Katayoon GHAEMI (CPPM)

61 Measuring cosmic bulk flow with kinetic Sunyaev-Zel'dovich (kSZ) velocity reconstruction

The average large-scale velocity of matter in the universe, known as bulk flow, is a fundamental test of the Cosmological Principle. Traditionally, this has been measured only out to $R\lesssim 100$ megaparsecs (Mpc). We present an application of kinetic Sunyaev-Zel'dovich (kSZ) velocity reconstruction to constrain bulk flow on cosmological scales more than $10\times$ larger, extending out to $R\sim 2000$ Mpc. kSZ velocity reconstruction isolates the Doppler shifting of CMB photons scattered by the electron plasma in galaxies to reconstruct the underlying velocity field.

We use galaxy data from two catalogs (unWISE and WISExSCOS) combined with CMB maps (from Planck) to reconstruct velocities in six redshift bins ranging from $0.1\lesssim z \lesssim 1.5$. We place some of the tightest constraints on bulk velocity at $500 \lesssim R\ [{\rm Mpc}] \lesssim 2000$, finding results fully consistent with the standard cosmological model, $\Lambda$CDM.

Furthermore, our constraints are relevant for the cosmic dipole anomaly, a persistent tension where measurements of galaxy number counts imply a bulk flow $\gtrsim 5\times$ larger than the standard theoretical expectation. Our constraints are in $\sim 2\sigma$ tension with the leading number-count dipole measurement from CatWISE, challenging their interpretation of the dipole anomaly as an excess coherent bulk flow, and reinforcing the standard cosmological model.

Speaker: Suroor Seher Gandhi (Perimeter Institute for Theoretical Physics)

15:00 Questions