Les supernovae de type Ia sont des chandelles standardisables : leurs distances retracent l’histoire de l’expansion de l’Univers jusqu’à un redshift d’environ 2. La plupart de mes tests indépendants de tout modèle partent des compilations de supernovae (JLA, Pantheon, Pantheon+ et DES), reconstruites par lissage itératif ou par processus gaussiens.
Combinées aux oscillations acoustiques baryoniques, aux mesures de croissance ou aux amas de galaxies, ces reconstructions testent la platitude de l’Univers, la métrique FLRW et la relativité générale. Elles aident aussi à identifier des effets systématiques, comme les hyper-paramètres des courbes de lumière ou la matrice de covariance de Pantheon+, et à prévoir ce qu’apporteront Rubin/LSST et Roman.
From a model-independent expansion history reconstructed from supernovae, we infer with iterative smoothing how the hydrostatic mass bias of galaxy clusters depends on mass and redshift, using X-ray gas fractions. Reconciling clusters with CMB constraints requires this bias to evolve with time.
arXiv:2603.13763Amas de galaxiesSupernovae IaLissage itératifAvec mes étudiants
L’Univers est-il plat ? Un test avec DESI DR2
We reconstruct distances and the Hubble rate from Pantheon+ and DES supernovae without assuming any dark energy model, and combine them with DESI DR2 baryon acoustic oscillations to test the FLRW metric and measure the spatial curvature. With Pantheon+ and DESI DR2 we find , consistent with flatness and with Planck 2018.
DOI · arXiv:2601.20293Articles clésCourbure et FLRWSupernovae IaBAOLissage itératifAvec mes étudiants
Des tests décisifs pour Rubin et DESI
Reconstructing the expansion history from simulated LSST supernovae and combining it with simulated DESI 5-year BAO, we forecast constraints of up to ±4% on the curvature and ±0.1 on , without assuming any form of dark energy.
DOI · arXiv:2407.07847Articles clésCourbure et FLRWSupernovae IaBAOLissage itératifPremier auteur
The best-fit ΛCDM of Pantheon+ is unusually small, and its residuals scatter less than the covariance matrix predicts, pointing to errors overestimated by about 7%. After accounting for this, no deviation from ΛCDM is found.
DOI · arXiv:2212.07917
Bien utiliser les processus gaussiens
The choice of mean function and hyperparameters biases Gaussian process reconstructions of supernova distances: a zero mean gives unphysical results and a best-fit ΛCDM mean biases them. Marginalising over a family of mean functions and over the hyperparameters removes the bias, whatever the kernel.
DOI · arXiv:2206.15081Articles clésSupernovae IaProcessus gaussiensAvec mes étudiants
Gaussian processes reconstruct the dark energy density from forecast stage-IV supernova, BAO and redshift-space-distortion data, assuming only a flat FLRW universe that becomes matter-dominated at high redshift, which also yields the growth history. Several dark energy models can be distinguished from ΛCDM at or more.
DOI · arXiv:2206.13820Énergie noireSupernovae IaBAOCroissance des structures (RSD)Processus gaussiens
On simulated Roman supernova data, Bayesian model selection finds the true model when it is among the candidates, but otherwise only picks the least wrong one. A frequentist test based on iterative smoothing can instead conclude that all tested models are false.
DOI · arXiv:2110.10977Énergie noireSupernovae IaLissage itératifSélection de modèles
Likelihood distributions derived from the non-parametric iterative smoothing method let us test a dark energy model and estimate its parameters without comparing it to an alternative. On WFIRST-like mocks we quantify how confidently different dark energy models can be distinguished.
DOI · arXiv:2009.12045Énergie noireSupernovae IaLissage itératifSélection de modèles
Reconstructing the expansion history from JLA supernovae with iterative smoothing while sampling the light-curve hyper-parameters, we find hyper-parameters consistent with those from ΛCDM, CPL and PEDE fits, and no significant redshift evolution.
DOI · arXiv:2001.10887
From redshift-space distortion data alone, we reconstruct the growth history with crossing statistics and Gaussian processes, derive the expansion history from it, and fit supernovae to constrain and . The results are consistent with flat ΛCDM and General Relativity.
DOI · arXiv:1906.05991Gravité modifiéeCroissance des structures (RSD)Supernovae IaProcessus gaussiensPremier auteur
Gaussian process regression can remove the bias in reconstructing from gravitational-wave standard sirens, and combined with supernovae it tests and ΛCDM. Dark-siren redshifts need close to spectroscopic precision to avoid significant bias.
DOI · arXiv:1905.10216
A model-independent analysis of the Pantheon supernovae shows deviations from ΛCDM at . They vanish with a simple Malmquist-like correction, but neither tests nor Gaussian processes find that this extra correction is statistically required.
DOI · arXiv:1812.03623
Combining model-independent expansion reconstructions from Pantheon supernovae and BAO, we test the FLRW metric and flatness, and use eBOSS DR14Q growth data to constrain , and . Everything is consistent with a flat FLRW universe, General Relativity and , with some tension at .
DOI · arXiv:1804.04320Articles clésCourbure et FLRWGravité modifiéeSupernovae IaBAOCroissance des structures (RSD)Lissage itératif
We reconstruct the expansion history from supernovae and fit growth-rate data to constrain , the growth index and without a dark energy model. The results agree with ΛCDM in General Relativity, and requiring a positive dark energy density tightens them further.
DOI · arXiv:1712.04865Articles clésGravité modifiéeSupernovae IaCroissance des structures (RSD)Premier auteurAvec mes étudiants
Tester ΛCDM sans le supposer
Combining BOSS DR12 BAO with JLA supernovae, we measure without assuming a cosmological model and introduce the diagnostic of the flat-FLRW metric. The results are consistent with a flat FLRW universe within .
DOI · arXiv:1606.06832Articles clésCourbure et FLRWSupernovae IaBAOLissage itératifPremier auteur