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Restriction of cosmological parameters using large-scale structure data

Grant number: 17/05549-1
Support type:Scholarships in Brazil - Post-Doctorate
Effective date (Start): October 01, 2017
Effective date (End): September 30, 2020
Field of knowledge:Physical Sciences and Mathematics - Physics - Elementary Particle Physics and Fields
Principal researcher:Nathan Jacob Berkovits
Grantee:Antonino Troja
Home Institution: Instituto de Física Teórica (IFT). Universidade Estadual Paulista (UNESP). Campus de São Paulo. São Paulo , SP, Brazil
Associated research grant:16/01343-7 - ICTP South American Institute for Fundamental Research: a regional center for theoretical physics, AP.TEM


Observations of the Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) of the Universe allow us to better understand the physics that drives the evolution of the primordial perturbation all the way to the large-scale distribution of galaxies we see today, leaving, however, important open problems. For example, the latest Planck results show that the Universe is composed only for the approx. 4% of the total energy density by ordinary baryonic matter. The remaining 96% is unknown, composed by non-baryonic matter (the so-called dark matter approx. 26%) and the mysterious dark energy (approx. 70%).It is impossible to directly observe dark matter, since it interacts only gravitationally. Since the galaxy distribution is the only observable in photometric surveys, we need to know as precisely as possible the relation between dark matter and galaxies. To this end, it is crucial to understand the statistical properties of the galaxy distribution. It is possible to describe the galaxy distribution as a non-Gaussian 3-dimensional field, in which non- Gaussianity arises from the highly non-linear clustering process, which introduces non-linear coupling between different scales.At first order, the galaxy distribution is analyzed by taking its power spectrum, i.e. the Fourier transform of the 2-point correlation function, which parametrizes the excess prob- ability of finding two galaxies at a certain distance. Unfortunately, the amplitude of the power spectrum (parametrized by the amplitude of dark matter fluctuations at 8h-1Mpc, sigma8) is degenerate with the bias parameters, leading to weak constraints. For this reason, the bispectrum is now one of the main tools in constraining cosmological parameters. Like the power spectrum, the bispectrum is the Fourier counterpart of 3-points correlation function, which parametrizes the excess probability of finding three galaxies in a given triangular configuration. The dependence of the cosmological parameters on a particular triangular configuration (equilateral, isosceles, squeezed, etc...) allows to constrain different parameters by taking different bispectrum configuration, thus removing the degeneracy.Following previous attempts, my idea is to analyze the photometric distribution of the galaxies, in order to constrain its angular spectrum and bispectrum . We can indeed treat the photometric galaxy distribution as a spherical field, allowing us to use angular statistics. Due to its power in removing degeneracy, in view of present and forthcoming photometric surveys like DES and Euclid, the angular bispectrum is likely to become one of the main tools in the analysis of photometric of datasets.The application of my estimator to real datasets could provide new constraints to cosmological parameters, for example bias and fNL. In view of this, the DES survey represents the best framework in which introduce the estimator I provided, in order to get stronger and statistical more reliable cosmological constraints comparing to the currently planned more traditional approach. (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
ANDRADE-OLIVEIRA, F.; CAMACHO, H.; FAGA, L.; GOMES, R.; ROSENFELD, R.; TROJA, A.; ALVES, O.; DOUX, C.; ELVIN-POOLE, J.; FANG, X.; et al. Galaxy clustering in harmonic space from the dark energy survey year 1 data: compatibility with real-space results. Monthly Notices of the Royal Astronomical Society, v. 505, n. 4, p. 5714-5724, . (17/05549-1, 19/04881-8)

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