Effects of primordial non-Gaussianity in the CMB and the large-scale structure

Open Access
Adhikari, Saroj
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
May 04, 2016
Committee Members:
  • Sarah Elizabeth Shandera, Dissertation Advisor
  • cosmology
  • early universe
  • cosmic microwave background
  • primordial non-Gaussianity
  • large-scale structure
We study the imprints and effects of non-Gaussian primordial perturbations in the cosmic microwave background (CMB) and the large-scale structure (LSS) of the Universe. Primordial non-Gaussianity, if detected, has the potential to discriminate between different classes of inflationary models. For example, inflationary models with just a single degree of freedom can be ruled out if long wavelength modes are found to be correlated with shorter wavelength modes. The effects of primordial non-Gaussianity can be seen in the CMB and the LSS---the two important observational probes of the primordial statistics and therefore the early universe. This thesis consists of studies in both of these observational probes. First, in the CMB front, we study the effect of primordial non-Gaussianity on the statistical anisotropy of the CMB temperature fluctuations. This is motivated by recent CMB results that indicate such statistical anisotropies at large CMB scales. We show that the probability of such observations increase in the case that primordial fluctuations are non-Gaussian. For this, we derive and use a general framework to describe statistical anisotropies in the power spectrum in the presence of primordial non-Gaussianity. We expect the formalism to be of use beyond the specific application that we have done. Second, in the large-scale structure front, we study the effect of primordial non-Gaussianity generated from two fields on the mass function of massive cluster of galaxies, scale-dependent halo bias, and large-scale stochasticity. We derive physically motivated analytic expressions for these observables and calibrate the derived expressions on dedicated N-body simulation results. Thus, the final outputs of the investigation are simulation calibrated semi-analytic formulas that can be used to constrain primordial non-Gaussianity beyond the simple single-field local-type that has been mostly studied up until this point. We also discuss the ``position-dependent bispectrum'' as an effective method of measuring the squeezed limit of a primordial trispectrum using large-scale structure galaxy surveys.