The precision of cosmological constraints derived from key observations in imaging surveys hinges on accurately measuring the true redshift distributions of tomographic redshift bins, particularly their mean redshifts.
Two approaches are commonly used. One involves using photometry with spectroscopic (or deep-photometry) counterparts. This approach is based on matching the fluxes of...
Interpretability and accuracy are pivotal challenges in the application of machine learning to cosmology. If machines find something humans don't understand, how can we check (and trust) the results? In this presentation, I contend that addressing this concern is not always obligatory, when machine learning is used to build an emulator of an expensive model. I will elucidate this argument...
With already more than 3,000 Type Ia supernovae (SNe Ia) ready for cosmology, ZTF will be in future years the state-of-the-art low-redshift sample needed to anchor Stage IV supernovae surveys, e.g. LSST.
I will first introduce the ZTF survey, as well as the DR2 SN Ia sample. I will then present an overview of DR2 results, which focuses on supernovae diversity and astrophysical biases. I...
The Dark Energy Spectroscopic Instrument (DESI) collaboration has recently released measurements of baryon acoustic oscillation (BAO) from the first year of observations.A joint analysis of DESI BAO, CMB, and SN Ia probes indicates a preference for time-evolving dark energy. We evaluate the robustness of this preference by replacing the DESI distance measurements at $z<0.8$ with the SDSS BAO...
Despite its global successes, the LambdaCDM standard model of cosmology
faces currently a number of tensions and anomalies, due to some
mismatch between early and late cosmic time physical representations. Indeed, in the era of precision cosmology, large scale inhomogeneities can no more be neglected. Fortunately, an exact GR solution exists, which is perfectly well suited for this purpose....
We present the Lemaitre project, an independent effort to measure the Dark
Energy equation of state (w,wa) using (1) a new set of type Ia supernovae (SNe
Ia) from the ZTF, SNLS (years 4 and 5), and Subaru/HSC surveys, covering the
redshift range 0.02 < z < 1.3, (2) a completely new cosmology inference
pipeline. The Lemaitre effort aims to address the tension between recent...
The galaxy cluster count is a particularly effective probe to constrain cosmological parameters and study the limits of the $\Lambda$CDM model. Indeed, the abundance of galaxy clusters is strongly correlated with cosmological parameters such as $\Omega_m$, $\sigma_8$, and the dark energy equation of state. Future surveys such as Euclid will enable us to acquire astrophysical data on a very...
The tension on the Hubble constant can be reformulated as a tension on the matter density parameter $\omega_M$. This has the advantage that $\omega_M$ is more directly connected to the CMB-derived parameters, unlike the Huble constant. With the recent DESI measurement, the tensoin is raised up to over6 $\sigma$, stronger than the tension on the Hubble constant.
Understanding the expansion of the Universe remains a profound challenge in fundamental physics. The complexity of solving General Relativity equations in the presence of intricate, inhomogeneous flows has compelled cosmological models to rely on perturbation theory in a homogeneous FLRW background. This approach accounts for a redshift of light encompassing contributions from both the...
The unprecedented statistics of detected Type Ia supernovae (SNe Ia) brought by the Zwicky Transient Facility (ZTF) enable us to probe the impact of the large-scale structure (LSS) on the properties of these objects. With a volume-limited selection of ZTF-Cosmo-DR2 SNe Ia overlapping with the SDSS-DR7 survey footprint, we investigated the distribution of their properties with regard to voids...
With the increase in data quality and quantity, the concordance cosmological model is under increasing tension. Therefore, it has become necessary to test the various hypotheses underlying the model: is the metric Friedman-Robertson-Lemaître-Walker? Is the Universe flat? Is dark energy the cosmological constant? Using state-of-the-arts data and analysis methods, I will show litmus tests of...
