Abstract
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 largescale 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 nonbaryonic matter (the socalled 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 nonGaussian 3dimensional field, in which non Gaussianity arises from the highly nonlinear clustering process, which introduces nonlinear coupling between different scales.At first order, the galaxy distribution is analyzed by taking its power spectrum, i.e. the Fourier transform of the 2point 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 8h1Mpc, 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 3points 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)
