Relativistic Effects and Novel Observables in Cosmology

9 Jul 2024, 08:30 → 12 Jul 2024, 14:35 Europe/Zurich

University of Geneva

Camille Bonvin, Julien Carron

The coming generation of surveys is expected to provide an incredible amount of data over a very large volume of the universe, allowing us to probe the laws of gravity, and the nature of dark matter and dark energy in an unprecedented way. The level of precision expected from these surveys, as well as the range of scales that will become accessible, necessitates a precise modelling of observables, including general relativistic effects. In parallel, it becomes crucial to develop new techniques and observables to extract information from these data, in an optimal and model-independent way. This workshop continues the series of meetings on GR effects that took place in Cape Town (2016), Zurich (2017), Sexten (2018), Zurich (2019) and Porto (2022). The idea is to extend the topic to include the development of novel observables and techniques in large-scale structure and CMB surveys, allowing to probe the fundamental properties of our universe.   

There are no conference fees; lunches and coffee breaks are offered to all participants. Due to space limitation, we may not be able to accept all applications.

zoom link: https://unige.zoom.us/j/69341889325

Meeting ID: 693 4188 9325

Organising committee: Camille Bonvin, Stefano Camera, Julien Carron, Chris Clarkson, José Fonseca and Roy Maartens

List of invited speakers

David Alonso (University of Oxford)

Luca Amendola (University of Heidelberg)

David Bacon (University of Portsmouth)

Emanuele Castorina (University of Milan)

Stefano Camera (University of Turin)

Julien Carron (University of Geneva)

Ruth Durrer (University of Geneva)

Enrique Gaztanaga (ICG Portsmouth & ICE/IEEC Barcelona)

Alex Hall (Royal Observatory Edinburgh)

Asta Heinesen (University of Copenhagen)

Martin Kunz (University of Geneva)

Ofer Lahav (University College London)

Julien Larena (University of Montpellier)

Francesca Lepori (University of Zurich)

Antony Lewis (University of Sussex)

Christian Marinoni (Aix-Marseille University)

Sabino Matarrese (University of Padova)

Cyril Pitrou (Institut d'Astrophysique Paris)

Yann Rasera (Paris Observatory)

Blake Sherwin (University of Cambridge)

Isaac Tutusaus (Midi-Pyrénées Observatory)

Jaiyul Yoo (University of Zurich)

 

Tuesday, 9 July

08:30 → 09:00 Registration

09:00 → 09:10 Welcome speech

Speaker: Camille Bonvin

info.pdf

09:10 → 10:40 Invited talks

Convener: Camille Bonvin

09:10 Testing General Relativity with cosmological large scale structure observations

General relativity has been tested in the solar system and with other astrophysical observations and passed all tests with flying colours. However, these were essentially tests of the vacuum Einstein equations. Cosmology is different. Not only do we test GR on much larger scales, but it is also a very essential non-vacuum solution of the theory.
Observing LSS we cannot only measure the density distribution and velocities, but, when considering relativistic effects, we can also measure the metric. In my talk I shall present a few examples on how LSS observations can provide tests of General Relativity.

Speaker: Ruth Durrer (Département de physique théorique, Université de Genève)

cosmoGR.pdf

09:40 Gravitational Redshift of Galaxies in Clusters

Speaker: Ofer Lahav

Lahav_GravZ_Geneva_9July2024.pdf

10:10 Predicting relativistic effects and constraining local Primordial Non-Gaussianities with galaxy surveys: a few lessons learnt

In this talk I will review recent work on understanding the importance of GR effects in the correlation function or power spectrum of spectroscopic data, with an emphasis on Infra-Red cancellations and their physical meaning. I will then discuss how any quantitative accurate statement about GR effects cannot be made without taking into account a large number of observational effects that become important at large scales. Finally, I will highlight some features of a power spectrum analysis searching for local Primordial Non-Gaussianities and their relation to GR effects.

Speaker: Emanuele Castorina

3_emanuele_Geneve.pdf

10:40 → 11:10 Coffee break

Coffee break

11:10 → 12:40 Short talks

Convener: Chris Clarkson (Queen Mary University of London)

11:10 GaPSE.jl: a model for the Galaxy Power Spectrum Estimator

In the next few years, the upcoming large-scale structure surveys such as DESI, Euclid, and particularly SPHEREx, are expected to significantly enhance sensitivity in detecting the signature of primordial local non-Gaussianities (PNG), through the scale-dependent bias on the large scale limit of the galaxy power spectrum.
However, on such large scales, this PNG could be confused with general relativistic (GR) effects arising from the full relativistic expressions of the galaxy number counts (GNC).
For this reason, we developed an open-source code, GaPSE.jl [1], that computes efficiently and accurately the observed power spectrum including GR and wide-angle effects, with any realistic survey geometry for single and multi tracers. In this talk, I will present the main features of GaPSE and its basic uses.

[1] Foglieni, Pantiri, Di Dio, Castorina, Large Scale Limit of the Observed Galaxy Power Spectrum (2023), Phys. Rev. Lett. 131, 111201, DOI: 10.1103/PhysRevLett.131.111201

Speaker: Matteo Foglieni (Leibniz Rechenzentrum)

presentation_GaPSE.pdf

presentation_GaPSE.pptx

11:25 General relativistic effects in the Spherical Fourier Bessel power spectrum with SPHEREx

SPHEREx is a full-sky galaxy survey that will launch in early 2025. It will detect ~500 Million galaxies over a redshift range 0 to ~4 with spectro-photometric redshifts. SPHEREx is designed to measure the scale-dependent galaxy bias due to primordial non-Gaussianity on large scales. However, general relativistic effects show a similar scale dependence in the power spectrum and are projected to have similar signal size as non-Gaussianity. Furthermore, typical power spectrum estimators are afflicted by wide-angle effects stemming from the geometry of the curved sky, and these wide-angle effects interact with relativistic effects. To avoid wide-angle effects, we use the spherical Fourier Bessel basis that is the harmonic basis in spherical coordinates, thus having a natural separation of angular and line-of-sight effects. This makes it the ideal basis for measuring large-scale perturbations and relativistic effects. I will present how GR effects such as lensing magnification enter the SFB power spectrum and how it affects the non-Gaussianity measurement, especially with an eye towards the SPHEREx mission.

Speakers: Henry Grasshorn Gebhardt (Caltech) , Yunfei (Robin) Wen (California Institute of Technology)

Gebhardt_Wen_Geneva_SPHEREx.pdf

11:40 Wide-angle and Doppler corrections to the power spectrum

The distortions in the galaxy number count introduced by perturbations in the spacetime can be measured by the Fourier power spectrum and bispectrum. The study of these spectra often uses the distant observer approximation where the line-of-sight (LOS) vectors are always parallel. But, it has been shown that going beyond this plane-parallel assumption introduces wide-angle corrections to the power spectrum and bispectrum. For the bisector LOS definition, the wide-angle effects are non-negligible and can potentially contaminate local f_{NL} measurements. In this work, we generalize the results, both in the single and multi-tracer cases, for all possible LOS definitions that can be parameterized by a free parameter in the power spectrum. We focus on low redshifts where the wide-angle effects are larger and therefore, we can safely neglect the lensing contribution. We consider the non-integrated redshift-space distortions and relativistic Doppler and Sachs-Wolfe terms in our perturbative expansion of the wide-angle corrections and include the primordial non-Gaussianity through the bias tracers.

Speaker: SECLOKA LAZARE GUEDEZOUNME (DEPARTMENT OF PHYSICS & ASTRONOMY, UNIVERSITY OF THE WESTERN CAPE, SOUTH AFRICA)

workshop_unige_July24_Guedezounme.pdf

11:55 The importance of accuracy in the modeling of large scale galaxy clustering

Future galaxy surveys will observe tens of million of sources over large fraction of the sky and various cosmic epochs. Currently, statistical analyses of galaxy distributions and their clustering are performed employing simplifying assumptions such as the flat sky and plane parallel ones. In order to obtain not only precise, but accurate analyses for future datasets, a more precise formalism will be required. In this talk I will show that a proper 3D modeling of galaxy correlations is needed in order to avoid systematic errors when performing tests of cosmological models with future large scale structure experiments.

Speaker: Francesco Spezzati (University of Padova)

SPEZZATI_GENEVE.pdf

12:10 Exact Modeling of Power Spectrum Multipole through Spherical Fourier-Bessel Basis

The three-dimensional galaxy power spectrum is a powerful probe of primordial non-Gaussianity and additional general relativistic effects, which become important on large scales. At the same time, wide-angle (WA) effects due to differing lines-of-sight (LOS) on the curved sky also become important with large angular separation. In this talk, we present a new way to non-perturbatively model WA and GR effects present in the commonly used power spectrum multipoles (PSM). We accurately model WA and GR effects using the spherical Fourier-Bessel (SFB) formalism, before transforming the result into the PSM. Moreover, for the first time, we can compute the analytical PSM Gaussian covariance on large scales, exactly including WA-induced mode-couplings, without resorting to any plane-parallel approximations.

Speaker: Yunfei (Robin) Wen (California Institute of Technology)

Wen_Geneva_GR.pdf

12:25 Cosmological cartography - The full-sky Spherical Fourier-Bessel power spectrum in general relativity

As our maps of Large Scale Structure increase in scale and precision and larger volumes are probed, it is crucial to properly model the observable quantities to construct robust predictions and maximize the information extracted by these new surveys. We present a full methodology for analyzing galaxy clustering on the lightcone with the 2-point correlation in the Spherical Fourier-Bessel (SFB) formalism. SFB is a natural choice to account for all wide-angle and relativistic (GR) effects, allowing to efficiently extract information from large volume galaxy surveys. We extend previous studies using SFB by including all projection and GR effects, and we develop an efficient numerical implementation that does not rely on commonly (mis)used approximations and includes a full non-diagonal covariance. We investigate the impact of neglecting GR corrections in cosmological parameter constraints, focusing on Primordial Non-Gaussianity and bias parameters. We also present a novel prescription for multi-bin correlations that allow to significantly boost the detectability of GR effects, opening a new window on general relativity testing.

Speaker: Federico Semenzato (University of Padova)

Semenzato_Geneva.pdf

12:40 → 14:00 Lunch break

14:00 → 15:30 Invited talks

Convener: Stefano Camera (Universita degli studi di Torino)

14:00 Novel biases in standard weak lensing and galaxy clustering analyses

Forthcoming weak lensing and galaxy clustering surveys, such as Euclid and LSST, offer unprecedented statistical precision. If new physics is to be discovered from these data sets, standard analysis methods that have previously sufficed must be carefully scrutinised. I will present recent calculations of several subtle biases that arise from neglecting non-linearity in the underlying density field and sub-optimal measurement choices. I will discuss how these effects might impact attempts to measure relativistic effects on large scales. Finally, I will look ahead to Euclid DR1, a rich data set for the community due for public release in 2026.

Speaker: Alex Hall (University of Edinburgh)

HALL_Geneva_2024.key

HALL_Geneva_2024.pdf

14:30 First measurement of the Weyl potential evolution from DES Y3 data

In this talk I will present a new methodology to measure the Weyl potential, which is the sum of the spatial and temporal distortions of the Universe's geometry, in a model independent way. I will then present how combining galaxy clustering and galaxy-galaxy lensing data from the Dark Energy Survey Year 3 measurements we can provide the first direct measurement of the evolution of the Weyl potential at four different redshifts. I will end by showing the forecast precision of such measurements with stage IV surveys.

Speaker: Isaac Tutusaus (IRAP-OMP)

itutusaus_Weyl_DESY3.pdf

15:00 Cosmic shear with Einstein rings

Massive galaxies, acting as gravitational lenses, can form greatly distorted images of background galaxies in so called strong lensing events. When background galaxy and lens are almost aligned along the line of sight, the image take the shape of an Einstein ring whose shape encodes basic properties of the lens. However, since lenses are not isolated objects in an otherwise perfectly homogeneous universe, these Einstein rings are sligthly altered by further weak lensing along the line of sight coming from the large scale matter distribution in the universe in front and behind the lens. This coupling between strong and weak lensing offers a novel opportunity to probe cosmic shear, in a regime that is not plagued by the same systematics as standard weak lensing shear. We will present this new method and its perspectives for the Euclid survey.

Speaker: Julien Larena (Université de Montpellier/ LUPM)

LOS_Shear_Geneva.pdf

15:30 → 16:00 Coffee break

16:00 → 17:45 Short talks

Convener: Enea Di Dio (University of Geneva)

16:00 A multi-tracer approach to constrain primordial non-Gaussianity: radio-optical synergies and the analysis of MeerKAT data

Speaker: Matilde Barberi Squarotti

Geneva_GR_MBS.pdf

16:15 Multipoles of the galaxy bispectrum on a relativistic light cone

New surveys of the large-scale structure will offer the chance to probe up to the Hubble scale to with percentage level precision. Therefore, in order to accurately infer information from these scales, we must consider percentage level corrections to our theoretical corrections that affect our observables. These include contributions from Doppler-type relativistic projection effects as well as wide separation effects, which are induced as we correlate points separated by large distances. In this talk we investigate these contributions to the bispectrum in some detail, including both wide angle effects and, for the first time, radial redshift effects. We show how they are intrinsically dependent on the choice of line of sight, and how we can make better choices of LOS to mitigate these effects. We investigate how they mix with the relativistic corrections and are of the same order, appearing similarly in the odd and even multipoles and can add additional relativistic signal through their mixing which is typically ignored. Further, if unaccounted for, we show they can mimic local type $f_{NL} \sim \mathcal{O}(10)$ in the worst cases.

Speaker: Christopher Addis (Queen Mary University of London)

Geneva.pdf

Geneva.pptx

16:30 Amplitude and Importance of Relativistic Contributions to the Galaxy Bispectrum

Upcoming galaxy surveys aim to map the universe with unprecedented precision, depth and sky coverage. The galaxy bispectrum is a prime source of information as it allows us to probe primordial non-Gaussianity (PNG), a key factor in differentiating various models of inflation. On the scales where local PNG is strongest, Doppler and other relativistic effects become important and need to be included. In this work, we investigate the detectability of relativistic and local PNG contributions in the galaxy bispectrum. We compute the signal-to-noise ratio for the detection of the bispectrum including such effects. Furthermore, we perform information matrix forecasts on the local PNG parameter fNL and on the parametrised amplitudes of the relativistic corrections. Finally, we quantify the bias on fNL from neglecting relativistic effects. Our results show that detections of both first- and second-order relativistic effects are promising with forthcoming spectroscopic survey specifications – and are largely unaffected by the uncertainty in fNL. Conversely, we show for the first time that neglecting relativistic corrections in the galaxy bispectrum can lead to almost 3σ bias on the detected value of fNL, highlighting the importance of including relativistic effects in our modelling.

Speaker: Samantha Rossiter (Università degli Studi di Torino)

Amplitude and importance of relativistic contributions to the galaxy bispectrum-2.pdf

16:45 Relativistic matter bispectrum of cosmic structures

Upcoming surveys of cosmic structures will probe scales ranging from the nonlinear regime to scales close to the cosmological horizon. This opens up the possibility of probing the ΛCDM model, as well as early universe scenarios with non-Gaussianity. Modeling the galaxy bispectrum is challenging, as it involves general relativity, radiation, and large nonlinearities. In this talk, I will present the latest developments we have achieved in the numerical and theoretical modeling of the matter angular bispectrum on the light cone, including relativistic and radiation effects. This is a crucial step towards modeling the observable bispectra, i.e., the galaxy number count bispectrum and the weak lensing bispectrum.

Speaker: Thomas Montandon (University of Montpellier)

ThomasMontandon_REgeneva.pdf

17:00 Relativistic effects and the streaming model

There are several effects that distort the clustering of galaxies, the largest of which being the well-known redshift-space distortion. In this talk I will discuss the more subtle effect of gravitational redshift. The impact of this non-kinematic effect in the auto-correlations is suppressed relative to RSD and is best probed in the odd multipoles of the cross-correlation function between distinct tracers. Here the dipole has emerged as the best prospect for detecting the gravitational redshift from large-scale structure. Recent work however has shown that the strongest detection will likely be from mildly nonlinear scales, presenting a modelling challenge. To this end, I will describe recent modelling efforts. In particular, I will show how to generalise the workhorse model of the correlation function, the so-called streaming model, to include in a compact way not only the gravitational redshift but several other important effects (wide-angle effects, evolution effects, nonlinearities, magnification bias, etc). Several insights related to computing correlations in redshift space will be discussed.

Speaker: Lawrence Dam (University of Geneva)

dam_geneva_july24.pdf

17:15 Relativistic dipole in galaxy-ellipticity correlations

We investigate the effects imprinted in a cross-correlation function between galaxy positions and intrinsic galaxy shapes (GI correlation). We present an analytical model of the GI correlation function, from which we find that the relativistic effects induce non-vanishing odd multipole anisotropies.We then estimate the signal-to-noise ratio and show that the GI dipole induced by the relativistic effects is detectable in future large-volume galaxy surveys.

Speaker: Shohei Saga (Kobayashi-Maskawa Institute)

saga.pdf

17:30 Towards Rigorous Modeling of Counts-in-Cells Statistics

We study the simplest non-perturbative statistics -- the one-point probability distribution function (PDF) for the averaged matter density inside spherical cells. The leading part to the PDF is defined by spherical collapse dynamics, whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from short modes and must be renormalized. We propose a new approach to renormalization by modeling the effective stress-energy tensor for short perturbations. The model contains three free parameters. Two of them are related to the counterterms in the one-loop matter power spectrum and bispectrum, one more parameterizes their redshift dependence. This relation can be used to impose priors in fitting the model to the PDF data. We confront the model with the results of high-resolution N-body simulations and find excellent agreement for cell radii $r_∗ ≥ 10\, {\rm Mpc/h}$ at all redshifts down to $z = 0$.

Additionally, we explore the sensitivity of the one-point PDF to the cosmological parameters. Our results suggest that our PDF model is sensitive to the value of $\sigma_8$ at the sub-per cent level. Another promising direction is to model the counterterm parameters in the Effective Field Theory of Large Scale Structure. Our PDF model provides comparable or better constraints on the counterterm coefficients than the correlation functions.

The talk is based on the published paper -- https://iopscience.iop.org/article/10.1088/1475-7516/2023/08/079.

Speaker: Anton Chudaykin (University of Geneva)

Relativistic_effects_pdf.pdf

Wednesday, 10 July

09:00 → 10:30 Invited talks

Convener: Nastassia Grimm (University of Geneva)

09:00 New observables in large-scale structure

In this talk I will discuss several new probes and considerations for large-scale structure measurements, which go beyond the most common 2x3pt shear and galaxy clustering measurements for cosmology. Firstly, I will discuss newly discovered cross-correlations between gravitational shear and flexion, including their surprising anticommutative properties. Secondly, I will discuss our latest understanding of cross-correlations between lensing and radio intensity mapping, which do not vanish due to foreground removal as might be supposed. Finally, I will discuss the latest higher order statistics LSS techniques and results in current cosmological surveys.

Speaker: David Bacon (University of Portsmouth)

Bacon Geneva.pdf

09:30 The many faces of scalar-tensor perturbation mixing in Cosmology

Going beyond linear perturbation theory in cosmology brings several novel phenomena, among which the unavoidable mixing of scalar and tensor perturbation modes. While some of such effects - such as the generation of the so-called Scalar-Induced-Gravitational-Wave background - are nowadays quite popular and largerly analyzed, there are other effects which are less known and deserve attention:
Tensor-Induced-Density-Perturbations, gravitational waves induced by scalar-tensor mixing, effects of scalar modes on the propagation of gravitational waves beyond the geometric optics limit.
I will review these various faces of non-linear perturbation theory in General Relativity, also mentioning some Modified Gravity extensions.

Speaker: Sabino Matarrese (Dipartimento di Fisica e Astronomia G. Galilei, Università degli Studi di Padova, Italy)

Matarrese_Geneva_2024.pdf

10:00 Covariant Cosmography with the Expansion Rate Fluctuations Field

Is it possible to construct a detailed model of local spacetime in a completely model-independent and non-perturbative manner? Specifically, this would involve developing an observationally viable and physically meaningful method for identifying and classifying angular distortions present in the distance-redshift relation, without relying on the cosmological principle or the notion of peculiar velocities. The first difficulty along this path is the meaningful generalization of the notion of the cosmic expansion rate at an arbitrary point P in a generic spacetime. This involves defining covariant cosmographic parameters, which are a set of line-of-sight dependent functions, with finite degrees of freedom, characterizing deviations from isotropy and critically dependent on the observer's state of motion. The second challenge revolves around the optimal estimation of anisotropies in the expansion rate using observational data. To this end, we define the expansion rate fluctuation field η, an observable designed to maximize measurement accuracy while minimizing potential biases.
Using analytical models, we analyze the virtues and limitations of this formalism. Current results and future survey prospects for constraining the shape of the expansion rate field in the local universe will also be presented.

Speaker: Christian Marinoni (Centre de Physique Théorique, Aix-Marseille Univ.)

Talk_geneva_Marinoni.pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Short talks

Convener: Stefano Camera (Universita degli studi di Torino)

11:00 Estimating covariant cosmographic parameters in the local universe

We present a comparative analysis of the fluctuation field in the expansion rate of the local universe ($z<0.1$) using galaxy samples (Cosmicflows-4) and supernova samples (Pantheon+). Employing spherical harmonic decomposition, we examine the anisotropy patterns across different redshift shells and observe a significant coherence in these patterns extending to the deepest regions investigated. We extract the multipole moments of relevant covariant cosmographic parameters characterizing the distance-redshift relation (up to third order in redshift).  We finally show how our analysis serves as a crucial tool for determining the motion of the matter-comoving frame relative to the cosmic microwave background (CMB) frame at varying distances from the terrestrial observer.

Speaker: Basheer Kalbouneh (Aix-Marseille university/ CPT)

11:15 Pantheon+ and friends: an insight on peculiar velocities probes

Peculiar velocities surveys are going to play a key role in testing our knowledge about the nearby universe and our cosmological assumptions. In this talk I will review some recent fundings and analysis that have been developped concerning these novel observables

Speaker: Francesco Sorrenti (University of Geneva - Cosmology Group)

sorrenti_conference.pdf

11:30 Fast and spurious: determining our peculiar velocity with galaxy surveys

To date, the most precise measurement of the observer's peculiar velocity comes from the dipole in the Cosmic Microwave Background. This velocity also generates a dipole in the source number counts. However its amplitude is unfortunately also sensitive to specific properties of the sources, that are difficult to determine precisely. Current studies give dipoles well aligned with the CMB dipole, but with a significantly larger amplitude. In this work, we develop an alternative method to measure our velocity from source counts, by using off-diagonal correlations between neighboring spherical harmonic coefficients. We show that these correlations contain both a term sensitive to the source properties and another more pristine one directly given by the observer velocity. We explore the potential of a Euclid-like survey to measure this second contribution, independently of the characteristics of the population of sources. We find that the method can reach a high enough sensitivity to decide the fate of the present "dipole tension", with a significance of up to 6 sigma. With conservative priors on the source properties, we can even reach a precision of ~4%, corresponding to a detection significance of 24 sigma.

Speaker: Fabien Lacasa (ULB - Université Libre de Bruxelles)

LacasaFabien-v2.pdf

11:45 Parity violation in the observed galaxy trispectrum

Recent measurements of the 4-point correlation function in large-scale galaxy surveys have found apparent evidence of parity violation in the distribution of galaxies. This cannot happen via dynamical gravitational effects in general relativity. If such a violation arose from physics in the early Universe it could indicate important new physics beyond the standard model, and would be at odds with most models of inflation. It is therefore now timely to consider the galaxy trispectrum in more detail. While the intrinsic 4-point correlation function, or equivalently the trispectrum, its Fourier counterpart, is parity invariant, the observed trispectrum must take redshift-space distortions into account. Although the standard Newtonian correction also respects parity invariance, we show that sub-leading relativistic corrections do not. We demonstrate that these can be significant at intermediate linear scales and are dominant over the Newtonian parity-invariant part around the equality scale and above. Therefore when observing the galaxy 4-point correlation function, we should expect to detect parity violation on large scales.

Speaker: Pritha Paul (Queen Mary University of London)

Geneva Presentation .pdf

Geneva Presentation .pptx

12:00 Examining Late-Time Anisotropy With Weak-Lensing B-Modes and Tomography

One of the cornerstones of the standard model of cosmology is the assumption that, on large scales, the Universe is homogeneous and isotropic. Some dark energy and modified gravity models, however, naturally lead to large-scale anisotropies. Thus, it is of great importance to test this broad assumption. One possible method of probing these anisotropies involves the use of weak gravitational lensing. More specifically, the imprints that these anisotropies would have on the weak shear of light beams on cosmological scales could be analysed in upcoming surveys like Euclid, SKA, and LSST. We outline how we applied the perturbative formalism developed by Pitrou et al. (arXiv:1503.01125,1503.01127) in order to estimate the magnitude of $B$-mode shear generated in the weak lensing signal by large-scale, late-time anisotropic expansion. We examine the possibility of using tomographic lensing in order to break the degeneracy between anisotropic expansion histories. Finally, we investigate how coupling between non-linearities and anisotropic expansion may affect observed $B$-mode power spectra.

Speaker: James Adam (University of the Western Cape)

James_Adam_Geneva_July_2024.pdf

12:15 Towards Classifying Our Universe with Neural Networks

In this talk, I will discuss the possibility of inferring properties of our Universe using a suitably trained neural network classifier. These properties can range from the nature of the gravitational interaction, to the energy content, to the presence of relativistic phenomena at cosmological scales. I will also discuss the difficulties faced by this approach, particularly in error modeling, and the ongoing work to overcome these.

Speaker: Benjamin Bose (University of Edinburgh)

Geneva_10.07_BenB.pdf

Geneva_10.07_BenB.pptx

Google slides link

12:30 → 14:00 Lunch break

14:00 → 16:00 Invited talks

Convener: Julien Carron

14:00 The ESA Euclid mission: status and outlook

In my presentation I will start with an overview of the Euclid satellite, discuss its current status and show some recent early results. I will then give a brief outlook of the expected science results in the coming years.

Speaker: Martin Kunz

Dropbox link to pptx

Euclid_07_2024_mk_unrolled.pdf

Euclid launch movie (dropbox)

14:30 The bispectrum of peculiar velocities.

Speaker: Stefano Camera (Universita degli studi di Torino)

StefanoCamera_GRinLSS_Geneva2024.pdf

15:00 Toward Robust Measurements of Relativistic Effects in Galaxy Clustering with DESI and Euclid

Gravitational redshift and Doppler effects give rise to an antisymmetric component of the galaxy correlation function when cross-correlating two galaxy populations or different tracers. Relativistic effects can be isolated from density and redshift space distortions (RSDs) clustering signals by splitting the galaxy population into two catalogs and using adapted estimators, such as the dipole of the cross-correlation function. Spectroscopic galaxy surveys, specifically the Dark Energy Spectroscopic Instrument (DESI) at low redshift and Euclid at higher redshift, will allow us to extract the signal with high significance across a wide range of scales. In this talk, I will discuss the prospects of measuring this observable in the near future. I will present forecasts for DESI and Euclid based on N-body simulations and discuss the potential challenges in modelling this signal on large and small scales.

Speaker: Francesca Lepori (University of Zurich)

Geneva2024_Lepori.key

Geneva2024_Lepori.key

Geneva2024_Lepori.pdf

15:30 The Black Hole Universe and Its Connection to the Einstein-Rosen Bridge

A homogeneous spherical cloud of pressureless matter ( M ) at rest will eventually collapse into a black hole characterized by its gravitational radius ( R_s = 2GM ). This forms what we term a Black Hole Universe (BHU). The BHU necessitates a boundary term to ensure that nothing can escape ( R_s ). This boundary term modifies Einstein’s field equations by adding a component that behaves identically to the observed cosmological constant (\Lambda = 3/R_s^2 ). Furthermore, we explore the quantum aspects of this boundary, offering a novel perspective on the Einstein-Rosen bridge. Our findings are supported by measurements of parity asymmetry in the Cosmic Microwave Background temperature perturbations, providing empirical evidence for this new theoretical framework.

Speaker: Enrique Gaztanaga (Institute of Cosmology and Gravitation, U. Portsmouth)

Geneva2024_gazta.pdf

16:00 → 16:30 Coffee break

16:30 → 18:00 Short talks

Convener: Camille Bonvin

16:30 Detecting Relativistic Doppler in Galaxy Clustering via Multi-tracing a Single Galaxy Population

The description of gravity, i.e. the theory of general relativity, plays a crucial role in our understanding of the universe. However, confirmations of the validity of this theory on cosmological scales have hitherto eluded us. In this context, 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 instead 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-scales usually plagued by cosmic variance. Cross-correlation power spectra seem to be much more promising than auto-correlation ones, due to the presence of the relativistic effect in a non-vanishing imaginary term that might be relevant even at intermediate scales. Moreover, relativistic Doppler is sample-dependent, so different galaxy populations display different contributions in their power spectra. In the search for the optimal galaxy samples to achieve a detection of the relativistic term, we can split a galaxy population according to luminosity, and even perform a multi-tracer analysis with auto-correlations of the two sub-samples and their cross-power spectrum. We are thus able to devise a technique enjoying multi-tracer benefits out of a single dataset and obtain a detection well above 5σ.

Speaker: Federico Montano (University of Turin)

FedericoMontano_Geneva2024_RelativisticEffectsConference.pdf

16:45 Accurate modeling of 3D large-scale galaxy clustering

Future surveys will measure galaxy clustering on unexplored regimes and with better than ever precision.
In my talk I will discuss some investigations on how this precision will be wasted if not matched by a comparable level of accuracy.
I will present the recent developement of a formalism for including radial modes information and new observables based on it.
Furthermore, I will show studies quantifying the mis-estimation of cosmological parameters when taking approximations that were acceptable until now but will not be for future surveys.
Finally, I will present a new proposal for a galaxy survey measuring the clustering at very high redshift.

Speaker: Alvise Raccanelli (University of Padova)

Modeling UTC Geneva 2024.key

Modeling UTC Geneva 2024.pdf

17:00 Unequal Time Effects in Large Scale Structure Correlators

Large scale structure correlators will be one of the most important probes of fundamental physics in the years to come. The results of redshift surveys which are used to measure these correlators sort their results into redshift bins for convenient analysis. In this short talk, we will discuss the implementation of corrections to account for differences in redshift between observables in the context of what we call field and spectrum level projections, which are built upon Fourier transforming expansions around assumed redshifts and deriving correlators from the ensuing fields.

Speaker: Theo Steele (University of Sussex)

Projection_Effects.pdf

17:15 Unequal-time corrections to the power spectrum

Upcoming galaxy survey data will reach unprecedented precision, which calls for a matching level of accuracy in the theoretical modeling of our observables. Recently, a novel formalism has been developed to account for unequal-time corrections in the two-point correlations, when the two objects being correlated are not at the same redshift. In this talk, for the first time, I include general relativistic effects in the formalism and I provide an estimate of the relevance of such corrections for future surveys.

Speaker: Eleonora Vanzan (University of Padova)

UT_Vanzan.pdf

17:30 Complex Evaluation of Angular Power Spectra - Case Study

The angular power spectrum is a key observable for upcoming high-precision cosmological surveys. However, modelling them typically involves the numerical evaluation of highly oscillatory 3-dimensional integrals that are computationally expensive using brute-force methods. In recent years, there has been increased interest in numerical methods that go beyond the well-known Limber approximation to robustly calculate angular power spectra in a wide parameter regime. Building on Picard-Lefshetz theory, we propose a new method to evaluate the angular power spectrum in the complex plane. Using a saddle point approximation, the computation is reduced to a one-dimensional integral, resulting in a significant increase in computation speed. This method elegantly complements the Limber approximation in the low-multipole regime and can be straightforwardly extended to include general integrands and redshift-space distortions. An application to typical survey kernels is presented. A publicly available code is under development.

Speaker: Benjamin Hertzsch (University of Edinburgh)

BHertzsch presentation.key

BHertzsch presentation.pdf

17:45 Simulating HI galaxies with Semi-Analytical Models in preparation for the SKAO late-time cosmology case

With the advent of next-generation radio observations, HI Galaxy surveys will be able to probe the late-time Universe with unprecedented sensitivity, offering the possibility to constraint cosmology in a complementary manner to standard spectroscopic surveys.
In preparation for this innovative scientific case, realistic simulations of large-sky volumes with good resolution are needed. In this talk I will discuss Semi-analytical models (SAM) that combine the advantages of relatively large box sizes and resolutions fine enough to resolve galaxy substructures. In particular, I will present a study of HI galaxies 21cm lines based on the state-of-the-art Galaxy Evolution and Assembly (GAEA) SAM. We employ the characteristic double-peak feature of the 21cm lines to obtain predictions for the HI Tully Fisher relation and validate the simulation by comparing to observations and exploring systematic effects. These type of study are key for understanding the realistic constraining power of peculiar velocity surveys with the SKAO. I will thus conclude discussing the next challenges and the roadmap for the future.

Speaker: Joël Mayor (ETH Zürich)

24-07-10_Relativistic_effects.pdf

Thursday, 11 July

09:00 → 10:30 Invited talks

Convener: Chris Clarkson (Queen Mary University of London)

09:00 Monopole fluctuations in galaxy surveys

Galaxy clustering provides a powerful way to probe cosmology. This requires understanding of the background mean density of galaxy samples, which is estimated from the survey itself by averaging the observed galaxy number density over the angular position. The angle average includes not only the background mean density, but also the monopole fluctuation at each redshift. Here for the first time we compute the monopole fluctuations in galaxy surveys. The monopole fluctuations vary as a function of redshift, and it is correlated with other fluctuations, affecting the two-point correlation function measurements. The rms fluctuation at z = 0.5 can be as large as 7% of the two-point correlation function in amplitude at the BAO scale, and it becomes smaller than 1% at z > 2. The monopole fluctuations are unavoidable, but they can be modeled. We discuss its relation to the integral constraint and the implications for the galaxy clustering analysis.

Speaker: Jaiyul Yoo (University of Zurich)

monopole_yoo.pdf

09:30 Cosmological Geometry and Gravity with non-linear clustering

A new avenue was recently developed for analyzing large-scale structure data with a model-independent approach, in which the linear power spectrum shape is parametrized with a large number of freely varying wavebands rather than by assuming specific cosmological models. Here we show, using a Fisher matrix approach, that the precision of this method for the case of the one-loop power spectrum is greatly improved with the inclusion of the tree-level bispectrum. We also show that accuracy can be similarly improved by employing perturbation theory kernels whose structure is entirely determined by symmetries instead of evolution equations valid in particular models (like in the usual Einstein-de Sitter approximation). We also present preliminary results of an application to real data from the BOSS survey. Finally, we show how these results can test cosmic geometry and gravity in a model-independent way.

Speaker: Luca Amendola (University Heidelberg)

Geneva2024.pdf

Geneva2024.pptx

10:00 High(ish)-redshift cosmology with the Quaia quasar catalog

Large-Scale Structure cosmology has made tremendous progress in the last few years, and is now able to place constraints on cosmological parameters with a precision rivalling that achieved by CMB experiments. In this process, the concordance Lambda CDM model has been shown to provide a very reasonable description of the evolution of the Universe's structure and expansion at late times. However, small cracks in the model have appeared, in the form of moderate tensions between parameters measured directly from low-redshift data and those inferred from the CMB. Elucidating the origin of these has been a key task for the community in the last few years. However, the evidence for these tensions comes, predominantly, from data at fairly low redshifts (distance ladder, cosmic shear). The intermediate-redshift universe (1<z<6) remains relatively unconstrained by current data, and its study may be able to throw light on the origin of these tensions, as well as provide key confirmation of the Lambda CDM predictions. I will discuss recent progress in our study of this regime using the Gaia - unWISE quasar catalog, Quaia, as well as prospects for future exploration of the mid-high-redshift Universe with this and other future datasets.

Speaker: David Alonso (University of Oxford)

Slides

10:30 → 11:00 Coffee break

11:00 → 12:30 Short talks

Convener: José Fonseca (Institute of Astrophysics and Space Sciences)

11:00 Infrared-safe cosmological probes in any gravity theory

A distinctive feature of relativistic effects in the cosmological probes is the presence of terms that scale with negative powers of $k$ relative to the matter density fluctuations. Perturbative calculations in $\Lambda$CDM have shown that the infrared divergences that these terms could in principle cause are cancelled out, in agreement with the equivalence principle.
In this talk, I will show that it is possible to derive a simple set of general conditions that control the infrared sensitivity of cosmological probes by working at linear order in relativistic perturbation theory and without assuming any gravity theory. Given the simplicity of our general conditions, I will show that it is possible to recover the $\Lambda$CDM cancellations mentioned above without performing any calculations. Finally, I will comment on the possibility of applying these conditions to gravity theories other than general relativity.
The importance of this work lies in the clear identification of the physical reasons that underlie the infrared sensitivity of the cosmological probes.

Speaker: Matteo Magi

INFRARED SENSITIVITY OF COSMOLOGICAL OBSERVABLES.pdf

11:15 Testing gravity through the distortion of time

The distribution of galaxies provides an ideal laboratory to test deviations from General Relativity. In particular, constraints on gravity modifications are commonly obtained by measuring the growth of cosmic structures through redshift-space distortions. However, such constraints rely on the validity of the weak equivalence principle, which has never been tested for the dark matter component. In my talk, I will show that dropping this restrictive assumption leads to severe degeneracies and makes it challenging to distinguish fundamental gravity modifications from interactions in the dark sector. Luckily, I will demonstrate that it is possible to break such degeneracies and recover tight constraints thanks to measurements of the distortion of time expected from upcoming galaxy surveys.

Speaker: Sveva Castello (University of Geneva)

SvevaCastello_Geneva_talk.pdf

11:30 Impact of Peculiar Velocities on Color Selection and the Large Scale Structure of Galaxy Surveys

In this study, we examine the novel effects of peculiar velocities on color selection in galaxy surveys, with a focus on their implications for the analysis of large-scale structure. Our work quantifies the interplay between the peculiar velocities of Emission Line Galaxies (ELGs) and the color filters employed in the DESI survey. We show that these velocities can shift spectral emission features into or out of filter bands, modifying galaxy colors and thereby influencing selection criteria. This phenomenon mimics the effect of evolution bias but can exceed it by as much as an order of magnitude. We illustrate that ELGs’ susceptibility to minor spectral shifts induced by peculiar velocities stems from their notably intense emission lines. Our results underscore that peculiar velocities markedly affect the ELG-LRG (Luminous Red Galaxy) multi-tracer dipole power spectrum and also impart smaller, yet significant, changes to the ELG single tracer statistics. This work highlights the essential need for careful consideration of spectral-dependent biases caused by peculiar velocities during the selection phase of galaxy surveys, to ensure an unbiased analysis of cosmological surveys.

Speaker: Batia Friedman-Shaw (Perimeter Institute)

relativistic_effects_friedman-shaw.pdf

11:45 Combining the Weyl potential and galaxy velocities: new measurements of E_G

The novel observable \hat{J}, capturing the evolution of the combined gravitational potential Ψ + Φ, provides a powerful and model-independent test of gravity. As I will demonstrate in this talk, its full capacity comes into play when being combined with further cosmological observables. Together with measurements of the growth of structure \hat{f}, accessible via redshift-space distortions, the quantity \hat{J} enables us to reconstruct the so-called E_G statistic. This statistic has been introduced as a robust consistency check of general relativity. However, previous measurements of E_G necessitated a single spectroscopic galaxy sample to measure both galaxy clustering and velocity-density correlations, to cancel the impact of the galaxy bias. In our recent work (NG, C. Bonvin & I. Tutusaus, 2024), we present a novel approach to measuring E_G which is free of this limitation: It directly combines two model-independent observables - \hat{f} and \hat{J}. Our method leads to four new measurements of E_G which provide a considerable improvement in precision compared to previous ones. We find a confirmation of general relativity at three redshifts, and a mild tension of 2.5\sigma at z=0.47.

Speaker: Nastassia Grimm (University of Geneva)

4_Grimm_Presentation_GRWorkshop.pdf

12:00 Non-Gaussianities in the Hubble-Lemaitre diagram

Local effects in a clumpy Universe affect photon paths and give rise to non-Gaussian features in the large-scale structure. We evaluate the higher-order moments for the distribution of the luminosity distance by adopting the averaging formalism on the past light cone. We compute the skewness in the Hubble-Lemaître diagram at the leading order in the cosmological perturbative expansion of the gravitational potential. In particular, we focus on perturbations of the luminosity distance due to gravitational lensing. We discuss our findings in view of recent numerical relativistic simulations, confirming that the skewness of the distance-redshift relation primarily originates from the late-time matter bispectrum as a signature of the interplay between photons and cosmic structures.

Speaker: Tiziano Schiavone (Galileo Galilei Institute for Theoretical Physics)

talk-Schiavone.pdf

12:15 Cross-correlations with gravitational waves in luminosity distance space

Third generation gravitational waves (GWs) observatories such as Einstein Telescope and Cosmic Explorer will yield an abundance of extra-galactic transient objects. Cross-correlations using GW merger events offer novel and powerful insights into the large-scale distribution of matter in the universe. These sources carry information on their luminosity distance, but remain uninformative about their redshifts; hence their clustering analyses and cross-correlations need to be carried out in luminosity distance space, as opposed to redshift space. Further, the large volumes accessible to these surveys imply that we may need to include relativistic corrections, such as lensing and Doppler magnification. However, the amplitude of these effects depends on the magnification and evolution biases of the transient sources, which are not yet understood. In this talk, I present a comparison of the number count angular power spectra between luminosity distance and redshift spaces, highlighting the inaccuracy of GWs clustering analysis when carried out in a different space, particularly at larger scales. Then, we employ Fisher forecasts to constrain the clustering, magnification and evolution biases of GWs from binary black hole (BBH) mergers in luminosity distance space, accounting for all relativistic effects. Constraining the bias parameters effectively implies constraining properties of the BBH population responsible for GWs emissions, thus potentially inferring both their redshift and mass distributions.

Speaker: Stefano Zazzera (Queen Mary University of London)

Zazzera_genevappt.pptx

zazzerapdf.pdf

12:30 → 14:00 Lunch break

14:00 → 15:30 Invited talks

Convener: Martin Kunz

14:00 Do we understand cosmic structure growth? Insights from new CMB lensing measurements with the Atacama Cosmology Telescope

One of the most powerful tests of our cosmological model is to verify the predicted growth of large-scale structure with time. Intriguingly, many recent measurements have reported tensions in such tests of structure growth, which could hint at systematic errors or even new physics. Motivated by this puzzling situation, I will present new determinations of cosmic structure growth using CMB gravitational lensing measurements from the Atacama Cosmology Telescope (ACT). These ACT DR6 CMB lensing measurements allow us to directly map the dark matter distribution in projection out to high redshifts; new cross-correlations of CMB lensing with unWISE and DESI galaxies also allow us to probe the matter tomographically. I will discuss the implications of our lensing results for the validity of our standard cosmological model as well as for key cosmological parameters such as the neutrino mass and Hubble constant.

Speaker: Blake Sherwin

GenevaWorkshopTalkBDSherwi.pdf

14:30 Spherical bispectrum expansion and quadratic estimators

Quadratic estimators (used notably for current most precise CMB lensing measurements) are a wide class of estimators efficient in capturing small signals of anisotropies. They will provide sub-percent contraints on the growth structure in the near future. After discussing how these estimators relate to bispectra, I will describe a general expansion of spherical (full-sky) bispectra into a set of orthogonal modes, with the aim to separate physically-distinct signals. The expansion uses a new set of discrete polynomials that are pairwise orthogonal with respect to the relevant Wigner 3j symbol, and reduce as desired to Chebyshev polynomials (i.e. Fourier series) in the flat-sky limit for both parity-even and parity-odd cases. We use the full-sky expansion to construct a tower of orthogonal CMB lensing quadratic estimators and construct estimators that are immune to foregrounds like point sources or noise inhomogeneities. In parity-even combinations (such as the lensing gradient mode from TT, or the lensing curl mode from EB) the leading two modes can be identified with information from the magnification and shear respectively, whereas the parity-odd combinations are shear-only.

Speaker: Julien Carron

Carron.pdf

15:00 How to measure lensing rotation

First-order gravitational lensing is a pure gradient, and hence only gives image magnification and shear. But post-Born corrections give rise to an additional small image rotation. I discuss the impact of this rotation on galaxies and the CMB temperature and polarization, and explain the challenges in trying to measure it. The rotation is somewhat enhanced for CMB lensing due to the large source path length, but remains small and very challenging to detect directly by CMB lensing reconstruction alone. I show the rotation may be detectable at high significance as a cross-correlation signal between the curl reconstructed with Simons Observatory (SO) or CMB-S4 data, and a template constructed from quadratic combinations of large-scale structure (LSS) tracers. I’ll give forecasts showing that in idealized cases this should be a new signal detectable at over 5 sigma with forthcoming data, and describe some of the theoretical complications. There is a follow-up talk by Mathew Robertson discussing more realistic cases and simulation results.

Speaker: Antony Lewis (University of Sussex)

Geneva24.pdf

Geneva24.pptx

15:30 → 16:00 Coffee break

16:00 → 17:00 Short talks

Convener: Julien Carron

16:00 CMB curl lensing

Lensing rotation (or curl lensing or shear B-modes) vanish at leading order in a concordance cosmology. However, it can be produced from sequential lensing events and is therefore a unique post-Born lensing observable. This rotation forms bispectra with other large-scale structure tracers, which can be leveraged to optimally probe the rotation as a cross-spectrum signal. I describe this process for the CMB lensing case, and with the aid of external tracers I will forecast the detection prospects for upcoming CMB experiments the Simons Observatory (SO) and CMB-S4. I also derive an equivalent curl estimator for the curved-sky, and present detailed validation of the methods using mock data from N-body simulations. This will include sensitivities to non-Gaussianities, state-of-the-art iterative lensing estimators, and robustness against extra-galactic foregrounds. I wrap up with some cosmology forecasts that would accompany a CMB curl detection.

Speaker: Mathew Robertson (University of Sussex)

Geneva_mr.pdf

Geneva_mr_split.pdf

16:15 Testing Gravity with cross-correlations of CMB and LSS

The accelerated expansion of the Universe is canonically attributed to the Dark Energy (DE), encapsulated in the Lambda factor in the Einstein field equations of gravity, but its nature is still not understood. While observations supply strong evidence in favor of the standard model of cosmology Lambda-CDM, a plethora of different modified gravity models (MG) can still arise and describe gravity and DE in another way than a Lambda-constant. In our work, we exploit the Effective Field Theory (EFT) framework which allows us to describe gravity and DE in a general way, encompassing single-field models. The strength of this approach is that we can describe not only general features of gravity but also recover model-dependent results through a mapping procedure. Upon this theoretical setting, we combine CMB and galaxy-clustering observables to discriminate between Lambda-CDM and MG/DE models. One of our main aims is to specifically assess the constraining power of cross-correlations between different probes from wide galaxy surveys, like Euclid, and the high sensitivity maps of the microwave sky delivered by Planck.

Speaker: Guglielmo Frittoli (Università Roma La Sapienza)

Guglielmo_Frittoli.pdf

16:30 Novel Bayesian Inferences from the Cosmic Microwave Background

In the evolving landscape of modern precision cosmology, the continuous progress of ongoing and upcoming surveys has provided us an unprecedented level of statistical power. Throughout my doctoral journey, I have mostly explored the Cosmic Microwave Background (CMB) at small angular scales, seeking to constrain cosmological parameters. My research has been dedicated to the development of robust and optimal estimators, poised to play a crucial role in current and future CMB surveys. In the first part, I will discuss how the motion of our observation frame impacts CMB fluctuations, specifically through aberration and modulation effects. These subtle effects at the smaller scales, violate the statistically isotropic nature of the CMB, and can be captured in the off-diagonal terms of the CMB covariance matrix in harmonic space. In a Bayesian approach, we have estimated our observation frame's motion from the Planck-2018 temperature data employing the Hamiltonian Monte Carlo (HMC) sampling technique. In the second part, I will explore the utilization of the CMB in probing galaxy clusters, which are the largest collapsed structures in the universe. What we are really curious about is figuring out how many of these clusters exist at different masses and ages (redshifts). But measuring their mass is not straightforward. So, we use the weak gravitational lensing of CMB to estimate how massive these clusters really are. In this talk, I present the power of the Maximum-a-posteriori (MAP) method, showcasing its enhanced precision in measuring cluster masses compared to traditional quadratic estimators (QE), for the upcoming CMB-Stage 4 experiment.

Speaker: Sayan Saha (Indian Institute of Science Education and Research (IISER), Dr. Homi Bhabha Road, Pune 411008, India)

Geneva_SAHA.key

Geneva_SAHA.pdf

16:45 non-Gaussian biases on CMB lensing reconstruction

We discuss the impact of non-linear matter clustering and post-Born lensing corrections to CMB lensing reconstruction for next generation surveys. In particular, we will explore the impact of non-Gaussian deflections on Maximum a Posteriori lensing estimators, which are able to provide optimal measurements of the lensing field, in contrast to quadratic estimators. Finally, we will discuss potential ways of mitigating biases.

Speaker: OMAR DARWISH

Short_CMBLensingiterative_nonGaussianity_Geneva_July_2024.pdf

Friday, 12 July

09:00 → 10:30 Invited talks

Convener: José Fonseca (Institute of Astrophysics and Space Sciences)

09:00 Relativistic effects down to non-linear scales: insights from the RayGal simulations

In this talk, I would like to highlight some key results from our RayGal studies of the impact of general relativistic effects on the apparent distribution of large-scale structures down to non-linear scales. We have investigated the dipole of the halo-halo cross-correlation from the 150 Mpc/h scale to the 5 Mpc/h scale. At large scales, we recover the linear expectation while at scales smaller than 30-60 Mpc/h the gravitational redshift contribution dominates together with non-trivial couplings. We have also investigated the impact of the magnification bias on the 3x2pts cross-correlation between gravitational convergence and the matter density field. At linear and quasi-linear scales, we recover Class analytical results while at smaller scales interesting deviations and effects appear (lensing bias, Finger-of-God effects, non-trivial couplings). I would be happy to discuss with workshop participants about new relativistic observables in the non-linear regime of structure formation.

Speaker: Yann RASERA (LUTH/Université Paris Cité/Observatoire de Paris/IUF)

Slides_RayGal_Relativistic_Geneva_Yann_Rasera_2024_v1.pdf

09:30 Global cosmological anisotropy as a long wavelength perturbation

The current concordance model of cosmology has been extremely successful in constraining the global properties of the universe. However, it is based on the assumption of statistical homogeneity and isotropy, and we are thus lead to test this global geometry. In practice, it is sufficient to constrain mild anisotropies, and I will show how anisotropy can be considered as a special long-wavelength perturbation around a Friedmann-Lemaître space-time. Within this framework, the same tools can be used to compute the anisotropic and non-stochastic perturbation, and the statistically isotropic and stochastic ones, allowing to test late anisotropy from all cosmological observables.

Speaker: Cyril Pitrou (CNRS, IAP)

Cyril_Pitrou_Geneve_2024.pdf

10:00 Redshift drift as an (almost) model-independent probe of dark energy

Real-time measurements are becoming feasible in cosmology, where the next generation of telescopes such as the Square Kilometer Array and the Extremely Large Telescope will detect the temporal change of redshifts of individual sources with a precision that will allow a direct detection of the cosmic expansion rate. These detections of cosmic drifts of redshifts are likely to become cornerstones in modern cosmology, where one has otherwise relied on the indirect inference of cosmic expansion by estimation of the slope of the fitted distance-redshift relation. Because of the direct inference of the cosmic time-evolution that is in principle possible with redshift drift, it is a powerful model-independent probe of the kinematics of the Universe. I will present formalism relevant for analysing redshift drift measurements model-independently, i.e., free of any explicit metric assumption. I will explain how one can use redshift drift observations to (almost) model-independently test for violations of the strong energy condition.

Speaker: Asta Heinesen (Niels Bohr Institute)

heinesen_Geneve.pdf

10:30 → 11:00 Coffee break

11:00 → 12:15 Short talks

Convener: Maria Berti (University of Geneva)

11:00 What makes a filament?

The cosmic web is the largest geometric structure in our universe, consisting of an intricate network of empty voids bounded by thin walls, elongated filaments, and dense clusters. Given the array of upcoming cosmological redshift surveys, new analytic tools are needed to study the formation of the various structures, quantify the geometry and topology, and isolate the elements of the cosmic web. New techniques might, for example, help to understand the link between the properties of galaxies and their placement in the large-scale structure. In this talk, I will present my recent developments in the study of the caustic skeleton of the cosmic web. By tracing the phase-space structure of the dark matter sheet, I identify the relevant caustics and illustrate their role in the cosmic web. I will propose a new definition of the filamentary structure of the large-scale structure in terms of the initial density fluctuations. This definition is based on the dynamics of the formation history and will help the systematic study of the properties and interplay of filaments, and their influence on the embedded galaxies.

Speaker: Job Feldbrugge (University of Edinburgh)

1_Job Feldbrugge Presentation.pdf

11:15 Cosmic Voids as Powerful Probe in Next-Generation Surveys

In recent years, cosmic voids have emerged as a promising new tool in cosmology, offering valuable insights complementary to galaxy 2-point statistics. However, to effectively utilize voids as cosmological probes to analyze the huge amount of data expected from upcoming surveys, robust statistical modeling is imperative. In this presentation, we introduce a novel combination of the excursion-set approach with peak theory formalism, providing accurate predictions for both halo and void statistics across a broad spectrum of scales. Specifically, we show that our theoretical framework yields halo mass functions and void size functions that closely match measurements obtained from simulations. Furthermore, we derive Lagrangian void density profiles that accurately match observations from cosmological simulations. Finally, we explore the potential of voids in precision cosmology within the context of upcoming galaxy surveys, such as Euclid and Roman, discussing their complementarity in probing dark energy density, equation of state, and massive neutrinos alongside other cosmological probes.

Speaker: Giovanni Verza (NYU)

Cosmic Voids as Powerful Probe in Next-Generation Surveys

voids_verza.pdf

11:30 Gravitational collapse, cosmic web and (almost) spherical cows

Despite more than a decade of effort, we still need to understand why our inference of cosmological parameters from early and late time Universe probes, most notably the value of the Hubble constant, differ. One of the reasons might be that the Universe, despite being homogeneous and isotropic on very large scales, is highly inhomogeneous at smaller ones, where we live and perform our measurements. In this talk, I will review the analytical tools employed to describe the evolution of the cosmic web, from the tiny fluctuations imprinted in the cosmic microwave background to the complex structures we observe today in the sky.
I'll focus on our understanding of the non-linear gravitational collapse based on a few simplifying assumptions, the most critical being spherical symmetry. I will show a recently proposed generalisation of the spherical collapse to an arbitrary anisotropic shape (described by the Bianchi IX geometry) and its impact on large-scale-structure physics. The emerging picture is one of a homogeneous Universe composed of almost spherical cows. We speculate on their collective behaviour and discuss how one of them, Laniakea, might bias our cosmological inference.

Speaker: Leonardo Giani (The University of Queensland)

Geneva12min.pptx

11:45 Light propagation through discrete dark matter and its relativistic effects

Light propagation in cosmology is usually studied in the geometrical optics approximation which requires the spacetime curvature to be much smaller than the light wavenumber. However, for non-fuzzy particle dark matter the curvature is concentrated in widely separated spikes at particle location. We consider a post-geometrical optics approximation that includes curvature and solve the Maxwell's equation in curved spacetime. We model the dark matter particle as interior Schwarzschild metric and propagate a plane light wave through it. For this, we numerically evolve (using the Einstein Toolkit framework) the Maxwell's equation in curved spacetime. Here, we expect to observe photons gaining a gravity-induced mass when travelling through dark matter, and light paths are not null nor geodesic.

Speaker: Annamalai P. Shanmugaraj (CP3-Origins, University of Southern Denmark)

Light_through_darkmatter_Annamalai.pdf

12:00 21cm IM with HIRAX: Simulation and Parameter Estimation

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio interferometer array currently in development, with an initial 256-element array to be deployed at the SARAO Square Kilometer Array (SKA) site in South Africa. Through 21cm Intensity Mapping, HIRAX will provide a cosmological survey of the distribution of the large-scale structure over the redshift range of $ 0.775 < z < 2.55$ over ~$15,000$ square degrees of the southern sky. I shall talk about parameter estimation for the Dark Energy EOS parameters, $w_0$ and $w_a$, particularly using an end-to-end simulation pipeline based on m-mode formalism for matter power spectrum estimation.

Speaker: Viraj Nistane (Université de Genève)

Geneva2024_VirajNistane.pdf

12:15 → 12:45 Summary talk

Convener: Roy Maartens (University of the Western Cape, South Africa)

12:15 Summary Talk

Speaker: Roy Maartens (University of the Western Cape, South Africa)

Geneva conf summary.key

12:45 → 14:15 Lunch break