arXiv subjects

Ludovic Van Waerbeke

Publications and source records attributed to Ludovic Van Waerbeke.

At least 19 recordsLinked to original sources

arXiv2026

DESI results and Dark Energy from QCD topological sectors

We present a physically motivated model of dark energy (DE) rooted in the topological structure of the Quantum Chromodynamics (QCD) vacuum. In this framework, DE arises from the difference between the QCD vacuum energy in an expanding Universe and in Minkowski spacetime, with the relevant contribution generated by tunnelling between distinct topological sectors. The QCD scale, $Λ_{\rm QCD}\sim100,{\rm MeV}$, naturally produces a vacuum-energy density of the same order of magnitude as the observed one, without introducing new fundamental fields, couplings, or fine-tuning. We show that the same mechanism can naturally accommodate an evolving dark-energy component. The resulting effective equation-of-state parameter $ω_{\rm DE}$ can evolve with redshift, lie on either side of $-1$, and cross the $ω_{\rm DE}=-1$ boundary, while asymptotically approaching $-1$ in the future. The framework offers a common physical origin for both the small amplitude of dark energy and its possible time evolution, the latter being suggested by recent DESI observations. Here, we develop the physical and cosmological aspects of the framework; its confrontation with cosmological data is presented in a companion paper.

astro-ph.CO↗

arXiv2026

Evolving Dark Energy Is Vacuum Energy After All

We investigate a physically motivated model of dynamical dark energy arising from the non-perturbative topological structure of the Quantum Chromodynamics (QCD) vacuum. The model introduces no new fundamental field or propagating degree of freedom: the dark energy (DE) density emerges as a global vacuum response to an expanding spacetime. We develop the first comprehensive cosmological implementation of this QCD-DE scenario and confront it with current observations, including Planck, ACT and SPT-3G cosmic microwave background data, DESI DR2 baryon acoustic oscillation measurements, and Type Ia supernova samples from Pantheon+ and DES-Dovekie. We compare the model with $Λ\mathrm{CDM}$ and $w_0w_a\mathrm{CDM}$ cosmologies. The model provides an excellent fit to the data and reproduces the late-time DE evolution preferred by DESI. The model naturally predicts effective phantom crossing behaviour at intermediate redshifts ($z\sim0.67$) while avoiding the instabilities associated with phantom scalar fields. Using goodness-of-fit statistics and Bayesian model-selection tools, including Akaike and Deviance Information Criteria and Bayesian evidence estimated from Markov-Chain Monte Carlo chains, we find that the QCD-induced model is consistently favoured over $Λ\mathrm{CDM}$ for the full combination of early and late-time datasets. Unlike the conventional descriptions of dynamical DE, support for QCD-DE in Bayesian evidence remains more consistent across datasets, suggesting that a physically motivated departure from a cosmological constant may provide a more economical description of the expansion history preferred by current observations.

astro-ph.CO↗

arXiv2026

The Glow of Axion Quark Nugget Dark Matter: (IV) CMB Spectral and Anisotropy Signatures

Axion quark nuggets (AQNs) are macroscopic dark-matter candidates, with masses of the order of a few grams to a kilogram and sub-micron radius, thought to form at the Quantum Chromo Dynamic era through axion-induced charge separation. This framework naturally links the dark and visible matter abundances ($Ω_{\rm DM} \sim Ω_{\rm visible}$) and provides a mechanism for generating the baryon-antibaryon asymmetry where dark matter is composed of matter AQNs and antimatter AQNs. Although behaving as cold dark matter on cosmological scales, baryons annihilate with antimatter AQNs, producing ionizing high-energy photons. The resulting energy injection may imprint spectral distortions on the cosmic microwave background (CMB) and modify the reionization history. Using a modified version of the \texttt{CLASS} Boltzmann code we compute the impact of this energy injection on the $μ$ and $y$ spectral distortion parameters as well as on the optical depth. We find that (1) the CMB anisotropies remain essentially unaffected by baryon annihilation, and (2) the associated spectral distortion signatures lie within the sensitivity reach of proposed CMB spectral distortion missions. Finally, we discuss the similarities and differences between the AQN scenario and annihilating or decaying dark matter models.

astro-ph.CO↗

arXiv2026

Probabilistic redshift estimation of unresolved galaxies from multi-band background light maps

Accurate knowledge of the redshift distributions of unresolved galaxy populations is essential for extracting the cosmological information encoded in the cosmic optical background. We present the first framework for estimating these distributions directly from multi-band maps of unresolved background light, using conditional normalising flows trained on realistic image simulations. For imaging qualities comparable to those expected from the synergy between the Euclid and Rubin LSST surveys, our model achieves sub-per cent accuracy in both the mean and standard deviation of the flux-weighted redshift distributions when the training and target samples are statistically well matched. Furthermore, the network proves highly resilient to incomplete photometric coverage when combined with tailored data imputation strategies. To address the challenge of statistical mismatches between simulations and real observations, we propose incorporating observational quantities into the target variables, providing a built-in diagnostic to assess model reliability and uncertainty from the predictions themselves. We also demonstrate the feasibility of map-based tomographic analyses, showing that the model retains sufficient pixel-level detail to recover redshift distributions for tomographically defined subsamples with near sub-per cent accuracy across all bins. These results establish conditional normalising flows as a viable tool for redshift estimation of unresolved sources, opening new opportunities for component separation, signal interpretation, and cosmological inference using multi-band optical background fluctuations.

astro-ph.CO↗

arXiv2026

Measuring satellite galaxy subhalo masses in redMaPPer clusters with UNIONS weak lensing data

In this work, we present the observed galaxy-galaxy lensing signal of satellite galaxies in rich clusters obtained from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). Such observations are crucial for understanding dark matter halo physics and interaction dynamics in the cluster environment. Our goal is to investigate the tidal stripping of cluster subhalos. Theoretical predictions, supported by recent studies, suggest that as satellite galaxies fall into clusters, their dark matter halos are stripped and dispersed into the cluster's main halo, while their stellar mass remains relatively intact. A robust method to probe this phenomenon is through statistical measurements of the excess surface mass density of satellite galaxies at different cluster-centric distances. Our results reveal a significant lensing signal, with strong statistical power from the large number of lens-source pairs. A simple model used in the fitting process to constrain subhalo masses effectively reproduces the observed lensing signal at relevant satellite-centric distances. However, it lacks the complexity to accurately fit the excess surface density at larger distances, where the host cluster halo dominates. We measure the subhalo-to-stellar mass ratio as a function of cluster-centric radius and find a strong positive trend. These results confirm tidal stripping or other environmental processes that impact the relative masses of a satellite galaxy's stellar component and its dark matter halo.

astro-ph.CO↗

arXiv2026

Revisiting the 'Lensing is Low' Problem with UNIONS

We present new measurements of the galaxy-galaxy lensing (GGL) signal around Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies using background sources from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). With high-quality imaging of background sources and a survey overlap of approximately 2650 square degrees, we obtain precise large-scale GGL measurements. Building on these new measurements, we revisit the so-called 'lensing is low' problem, wherein galaxy-halo connection models calibrated on galaxy clustering (GC) data over-predict the GGL signal by 20-40% assuming CMB-based cosmological parameters. We model the galaxy-halo connection using a halo occupation distribution (HOD), and perform joint fits to both GGL and GC signals across a wide range of scales, as well as a GC-only fit. In contrast to previous work, we do not find a significant 'lensing is low' effect in the CMASS sample, although the best joint fits are achieved by decreasing the amplitude of the matter power spectrum slightly relative to the Planck cosmological parameters. Overall, we find that two models describe our observables similarly well: one where HOD and cosmological parameters are free, and one where HOD, cosmological, and feedback parameters are free. Importantly, we emphasise the role of large scales in constraining the lensing is low effect, shifting the narrative away from an exclusively small-scale issue.

astro-ph.CO↗

arXiv2026

QCD-driven dark matter: AQNs formation and observational tests

The nature of dark matter remains a central problem in cosmology. A compelling possibility is that dark matter is macroscopic, consisting of composite objects formed in the early Universe. We introduce the QCD-AQN framework, a well-motivated scenario in which dark matter is composed of dense aggregates of quark and antiquark matter stabilised by axion domain walls. The framework proposes a unified explanation for both dark matter and the observed matter-antimatter asymmetry. Particular emphasis is placed on existing observational constraints and on observational tests. Finally, we explore a possible QCD-based scenario for dark energy.

hep-ph↗

arXiv2025

Cluster properties as a function of dynamical state in the DESI Legacy x UNIONS surveys

We investigate how the dynamical state of galaxy clusters influences their galaxy populations and mass distributions. Using photometrically selected clusters from the DESI Legacy Imaging Survey cross-matched with the UNIONS galaxy shear catalogue, we classify clusters as evolved or evolving based on their rest-frame r-band magnitude gaps and stellar mass ratios between the brightest cluster galaxies (BCGs) and bright satellites. We measure the stellar mass functions, weak-lensing profiles, and radial number density and red-fraction profiles of stacked clusters in both subsamples. Evolved clusters exhibit more concentrated lensing profiles, bimodal stellar mass functions dominated by massive BCGs, and a deficit of intermediate-mass satellites, while evolving clusters show flatter central lensing signals and an excess of massive satellites. Applying the same selection to IllustrisTNG clusters reproduces these trends and links the observed differences to distinct mass accretion histories. These results demonstrate the close link between cluster galaxy populations and the overall dynamical state of their underlying dark matter halo.

astro-ph.GA↗

arXiv2025

The Glow of Axion Quark Nugget Dark Matter: (III) The Mysteries of the Milky Way UV Background

Axion quark nuggets (AQNs) are hypothetical objects with nuclear density that would have formed during the quark-hadron transition and could make up most of the dark matter today. These objects have a mass greater than a few grams and are sub-micrometer in size. They would also help explain the matter-antimatter asymmetry and the similarity between visible and dark components of the universe, i.e. $Ω_{\text{DM}} \sim Ω_{\text{visible}}$. These composite objects behave as cold dark matter, interacting with ordinary matter and producing pervasive electromagnetic radiation. This work aims to calculate the FUV electromagnetic signature in a 1 kpc region surrounding the solar system, resulting from the interaction between antimatter AQNs and baryons. To this end, we use the high-resolution hydrodynamic simulation of the Milky Way, FIRE-2 Latter suite, to select solar system-like regions. From the simulated gas and dark matter distributions in these regions, we calculate the FUV background radiation generated by the AQN model. We find that the results are consistent with the FUV excess recently confirmed by the Alice spectrograph aboard New Horizons, which corroborated the FUV excess initially discovered by GALEX a decade ago. We also discuss the potential cosmological implications of our work, which suggest the existence of a new source of FUV radiation in galaxies, linked to the interaction between dark matter and baryons.

astro-ph.CO↗

arXiv2025

Cosmology from UNIONS weak lensing profiles of galaxy clusters

Cosmological information is encoded in the structure of galaxy clusters. In Universes with less matter and larger initial density perturbations, clusters form earlier and have more time to accrete material, leading to a more extended infall region. Thus, measuring the mean mass distribution in the infall region provides a novel cosmological test. The infall region is largely insensitive to baryonic physics, and provides a cleaner structural test than other measures of cluster assembly time such as concentration. We consider cluster samples from three publicly available galaxy cluster catalogues: the Spectroscopic Identification of eROSITA Sources (SPIDERS) catalogue, the X-ray and Sunyaev-Zeldovich effect selected clusters in the meta-catalogue M2C, and clusters identified in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey. Using a preliminary shape catalogue from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS), we derive excess surface mass density profiles for each sample. We then compare the mean profile for the DESI Legacy sample, which is the most complete, to predictions from a suite of simulations covering a range of $Ω_{\rm m}$ and $σ_8$, obtaining constraints of $Ω_{\rm m}=0.34\pm 0.06$ and $σ_8=0.77 \pm 0.04$. We also measure mean (comoving) splashback radii for SPIDERS, M2C and DESI Legacy Imaging Survey clusters of $1.39^{+0.21}_{-0.18} {\rm cMpc}$, $1.77^{+0.20}_{-0.18} {\rm cMpc}/h$ and $1.42^{+0.11}_{-0.12} {\rm cMpc}/h$ respectively. Performing this analysis with the final UNIONS shape catalogue and the full sample of spectroscopically observed clusters in DESI, we can expect to improve on the best current constraints from cluster abundance studies by a factor of 2 or more.

astro-ph.CO↗

arXiv2025

UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey

The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program.

astro-ph.GA↗

arXiv2024

UNIONS: a direct measurement of intrinsic alignment with BOSS/eBOSS spectroscopy

During their formation, galaxies are subject to tidal forces, which create correlations between their shapes and the large-scale structure of the Universe, known as intrinsic alignment. This alignment is a contamination for cosmic-shear measurements as one needs to disentangle correlations induced by external lensing effects from those intrinsically present in galaxies. We constrain the amplitude of intrinsic alignment and test models by making use of the overlap between the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) covering $3500 \, \mathrm{deg}^2$, and spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS/eBOSS). By comparing our results to measurements from other lensing surveys on the same spectroscopic tracers, we can test the reliability of these estimates and verify they are not survey dependent. We measure projected correlation functions between positions and ellipticities, which we model with perturbation theory to constrain the commonly used non-linear alignment model and its higher-order expansion. Using the non-linear alignment model, we obtain a $13σ$ detection with CMASS galaxies, a $3σ$ detection with LRGs, and a detection compatible with the null hypothesis for ELGs. We test the tidal alignment and tidal torque model, a higher-order alignment model, which we find to be in good agreement with the non-linear alignment prediction and for which we can constrain the second-order parameters. We show a strong scaling of our intrinsic alignment amplitude with luminosity. We demonstrate that the UNIONS sample is robust against systematic contributions, particularly concerning PSF biases. We reached a reasonable agreement when comparing our measurements to other lensing samples for the same spectroscopic samples. We take this agreement as an indication that direct measurements of intrinsic alignment are mature for stage IV priors.

astro-ph.CO↗

arXiv2024

The Glow of Axion Quark Nugget Dark Matter: (I) Large Scale Structures

Axion quark nuggets (AQNs) are hypothetical objects with a mass greater than a few grams and sub-micrometer size, formed during the quark-hadron transition. Originating from the axion field, they offer a possible resolution of the similarity between visible and dark components of the Universe. These composite objects behave as cold dark matter, interacting with ordinary matter and resulting in pervasive electromagnetic radiation throughout the Universe. This work aims to predict the electromagnetic signature in large-scale structures from the AQN-baryon interaction, accounting for thermal and non-thermal radiations. We use Magneticum hydrodynamical simulations to describe the distribution and dynamics of gas and dark matter at cosmological scales. We calculate the electromagnetic signature from radio, starting at $ν\sim$ 1 GHz, up to a few keV X-ray energies. We find that the AQNs signature is characterized by monopole and fluctuation signals. The amplitude of both signals strongly depends on the average AQN mass and the ionization level of the baryonic environment. We identify a most optimistic scenario with a signal often near the sensitivity limit of existing instruments, such as FIRAS and the South Pole Telescope for high-resolution. Fluctuations in the Extra-galactic Background Light caused by the AQN can be tested with space-based imagers Euclid and James Webb Space Telescope. We also identify a minimal configuration, still out of reach of existing instruments, but future experiments might be able to pose constraints on the AQN model. We conclude that this is a viable dark matter model, which does not violate the canons of cosmology, nor existing observations. The best chances for testing this model reside in 1) ultra-deep IR and optical surveys, 2) spectral distorsions of the CMB and 3) low-frequency (1 GHz < $ν$ < 100 GHz) and high-resolution ($\ell > 10^4$) observations.

astro-ph.CO↗

arXiv2024

The Glow of Axion Quark Nugget Dark Matter: (II) Galaxy Clusters

(abridged) We analyze the emission of axion quark nuggets in a large sample of 161 simulated galaxy clusters using the SLOW simulation. These clusters are divided into a sub-sample of 150 galaxy clusters, ordered in five mass bins ranging from $0.8$ to $31.7 \times 10^{14} \,M_\odot$, along with 11 cross-identified galaxy clusters from observations. We investigate dark matter-baryonic matter interactions in galaxy clusters in their present stage at redshift $z=0$ by assuming all dark matter consists of axion quark nuggets. The resulting electromagnetic signatures are compared to thermal Bremsstrahlung and non-thermal cosmic ray synchrotron emission in each galaxy cluster. We further investigate individual frequency bands imitating the observable range of the WMAP, Planck, Euclid, and XRISM telescopes for the most promising cross-identified galaxy clusters hosting detectable signatures of axion quark nugget emission. We propose that the Fornax and Virgo clusters represent the most promising candidates to search for axion quark nugget emission signatures.

astro-ph.CO↗

arXiv2023

Exploring the mass and redshift dependence of the cluster pressure profile with stacks on thermal SZ maps

We provide novel constraints on the parameters defining the universal pressure profile (UPP) within clusters of galaxies, and explore their dependence on the cluster mass and redshift, from measurements of Sunyaev-Zel'dovich Compton-$y$ profiles. We employ both the $\textit{Planck}$ 2015 MILCA and the ACT-DR4 $y$ maps over the common $\sim 2,100\,\text{deg}^2$ footprint. We combine existing cluster catalogs based on KiDS, SDSS and DESI observations, for a total of 23,820 clusters spanning the mass range $10^{14.0}\,\text{M}_{\odot}<M_{500}<10^{15.1}\,\text{M}_{\odot}$ and the redshift range $0.02<z<0.98$. We split the clusters into three independent bins in mass and redshift; for each combination we detect the stacked SZ cluster signal and extract the mean $y$ angular profile. The latter is predicted theoretically adopting a halo model framework, and MCMCs are employed to estimate the UPP parameters, the hydrostatic mass bias $b_{\rm h}$ and possible cluster miscentering effects. We constrain $[P_0,c_{500},α,β]$ to $[5.9,2.0,1.8,4.9]$ with $\textit{Planck}$ and to $[3.8,1.3,1.0,4.4]$ with ACT using the full cluster sample, in agreement with previous findings. We do not find any compelling evidence for a residual mass or redshift dependence, thus expanding the validity of the cluster pressure profile over much larger $M_{500}$ and $z$ ranges; this is the first time the model has been tested on such a large (complete and representative) cluster sample. Finally, we obtain loose constraints on the hydrostatic mass bias in the range 0.2-0.3, again in broad agreement with previous works.

astro-ph.CO↗

arXiv2022

X-ray annual modulation observed by XMM-Newton and Axion Quark Nugget Dark Matter

The XMM-Newton observatory shows evidence, with a 11$σ$ confidence level, for seasonal variation of the X-ray background in the near-Earth environment in the 2-6 keV energy range (Fraser et al. 2014). The authors argue that the observed seasonal variation suggests a possible link with dark matter. We propose an explanation which involves the Axion Quark Nugget (AQN) dark matter model. In our proposal, AQNs can cross the Earth and emit high energy photons at their exit. We show that the emitted spectrum is consistent with (Fraser et al. 2014), and that our calculation is not sensitive to the specific details of the model. Our proposal predicts a large seasonal variation, on the level of 20-25%, much larger than conventional dark matter models (1-10%). Since the AQN emission spectrum extends up to $\sim $ 100 keV, well beyond the keV sensitivity of XMM-Newton, we predict the AQN contribution to the hard X-ray and $γ$-ray backgrounds in the Earth's environment. The Gamma-Ray Burst Monitor (GBM) instrument, aboard the FERMI telescope, is sensitive to the 8 keV-40 MeV energy band. The NuSTAR (Nuclear Spectroscopic Telescope Array) is a NASA space based X ray telescope which operates in the range 3 to 79 keV is also sensitive to higher energy bands. We suggest that the multi-year archival data from the GBM or NuSTAR could be used to search for a seasonal variation in the near-Earth environment up to 100 keV as a future test of the AQN framework.

astro-ph.HE↗

arXiv2022

ShapePipe: a new shape measurement pipeline and weak-lensing application to UNIONS/CFIS data

UNIONS is an ongoing collaboration that will provide the largest deep photometric survey of the Northern sky in four optical bands to date. As part of this collaboration, CFIS is taking $r$-band data with an average seeing of 0.65 arcsec, which is complete to magnitude 24.5 and thus ideal for weak-lensing studies. We perform the first weak-lensing analysis of CFIS $r$-band data over an area spanning 1700 deg$^2$ of the sky. We create a catalogue with measured shapes for 40 million galaxies, corresponding to an effective density of 6.8 galaxies per square arcminute, and demonstrate a low level of systematic biases. This work serves as the basis for further cosmological studies using the full UNIONS survey of 4800 deg$^2$ when completed. Here we present ShapePipe, a newly developed weak-lensing pipeline. This pipeline makes use of state-of-the-art methods such as Ngmix for accurate galaxy shape measurement. Shear calibration is performed with metacalibration. We carry out extensive validation tests on the Point Spread Function (PSF), and on the galaxy shapes. In addition, we create realistic image simulations to validate the estimated shear. We quantify the PSF model accuracy and show that the level of systematics is low as measured by the PSF residuals. Their effect on the shear two-point correlation function is sub-dominant compared to the cosmological contribution on angular scales <100 arcmin. The additive shear bias is below 5x$10^{-4}$, and the residual multiplicative shear bias is at most $10^{-3}$ as measured on image simulations. Using COSEBIs we show that there are no significant B-modes present in second-order shear statistics. We present convergence maps and see clear correlations of the E-mode with known cluster positions. We measure the stacked tangential shear profile around Planck clusters at a significance higher than $4σ$.

astro-ph.CO↗

arXiv2021

Constraining AGN feedback model with SZ profile

Relativistic jets from AGN have a wide range of impacts on galaxy groups and clusters and are key for understanding their formation and physical properties. However, this non-gravitational process is not well understood. Galaxy groups with shallow gravitational potentials are ideal laboratories to study and constrain the AGN feedback model. We studied hot gas in ~66,000 SDSS LRG halos with an average halo mass of 3 x 10^13 Msun using the Planck tSZ map. We have detected their average tSZ radial profile at ~17 sigma and compared it with the cosmo-OWLS cosmological hydrodynamical simulations with different AGN feedback models. The best agreement has been obtained for the AGN 8.0 model in the simulations. We have also compared our measured tSZ profile with the prediction from the universal pressure profile assuming the self-similar relation and found them consistent if the model accounts for the clustering of neighboring haloes via a two-halo term.

astro-ph.CO↗