Resumen de Cross-correlations in the dark energy survey: from redshift distribution inference to probes of gravity with the cosmic microwave background
During the past decades, we have been witnesses to unprecedented advances in the understanding of our universe dynamics and evolution. Indeed, together with the theory of General Relativity (GR) by Albert Einstein 100 years ago, the improvement of observational tools have led to the establishment of the Standard Model of Cosmology, the so-called $\Lambda$-Cold-Dark-Matter ($\Lambda CDM$), model which is so far the simplest model that describes best our universe, considering the observations. However, this standard model suffers from caveats, more specifically the presence in the theory of two unknown components, Dark Energy and Dark Matter. Understanding the mystery behind these two components has become the leading objective of observational cosmology today, and of current experiments, as it is the case of the Dark Energy Survey (DES), that will after six years of observations image about 300 million galaxies with an unprecedented depth covering one eighth of the sky ($5000$ sq. deg.). This thesis is based on the analysis of the first year of observation of DES (DESY1) and more in particular on the use of cross-correlation techniques in cosmological analyses. Here, we expose two different uses of cross-correlations. Namely, we first show how cross-correlation techniques have been employed as a tool to infer the redshift distribution of objects using the so-called clustering-redshift methodologies. And, moreover, how for the first time these techniques have entered the cosmological analyses to correct the mean of the redshift distributions of the DESY1 galaxy catalog with measured shapes (the weak lensing sample) inferred by typical photometric techniques. We explain how using simulations we have evaluated the systematics errors induced by our methodology and present the full methodology employed for redshift distribution determination of the DESY1 Weak lensing sample. Secondly, we show how we have been using cross-correlations as a probe of the $\Lambda CDM$ cosmology measuring the cross-correlation between cosmic voids identified in the DESY1 catalogs and the lensing map from the Planck satellite. More specifically, recent results have suggested an excess signal in the observed imprint of void catalogs in the Cosmic Microwave Background temperature maps with respect to the $\Lambda CDM$ predictions. We reiterate the procedure using this time the lensing maps of the CMB. After optimizing our void catalogs in simulations, looking for populations of voids responsible for the more significant detection, we detect the imprint of DESY1 cosmic voids with a significance of $\sim 7-12\sigma$ with a discrepancy of $\sim 3-9\sigma$, with respect to $\Lambda CDM$ simulations.
