Sharif Digital Repository

This thesis is divided into two major parts. In the first half of the thesis we introduce and study primordial non-Gaussianity in the context of Inflationary Cosmology. Most recent cosmological observations indicate that Universe has experienced an inflationary phase during its very early moments of existence. Not only Inflation is a possible solution of FRW cosmology problems, but also it acts as the generator of all the structure in the Universe. According to standard Inflationary cosmology, the primordial fluctuations which are considered to be the seeds of the entire structure in the Universe are scale-invariant, adiabatic and Gaussian.However there is the possibility to have an... 

The observations of the cosmic background radiation and large-scale structures show that the standard cosmological model is in good agreement with observational data. The standard model is based on the cosmological constant, dark matter, and Gaussian, nearly scale-invariant, adiabatic, and isotropic initial conditions. Although this model has been phenomenologically successful, but the problems of dark energy, dark matter, missing baryons and early universe remain unresolved. One of the most important theoretical questions in cosmology is whether the cosmological constant is the reason for accelerated cosmic expansion. In other words, is Einsteinian gravity the correct theory on the cosmic... 

One of the most important studies in cosmology is the study of Large Scale Structure of cosmos, where one of the useful and valuable tools is Excursion Set Theory(EST). EST or Extended Press-Schechter is a theory based on stochastic processes which gives us the distribution function(mass function) of dark matter halos. In order to having smoothed density feld Excursion Set Theory uses a specifc window function(flter) called sharp k-space, which is a top-hat in Fourier space. If one use this specifc window function the process of density feld with respect to variance will be a Markov process, with any other window function the process won’t be a Markov process. Excursion Set Theory using the... 

The standard model of cosmology with nearly Gaussian, isotropic, scale invariant and adiabatic initial conditions describes the cosmological observations. However, the study of any deviation from the mentioned conditions will open up a new window to the physics of early universe. In this work we study the effect of the oscillatory and step in potential inflationary models in late time large scale structure observations. Almost we study the matter power spectrum, number density of the structures, the halo bias an the bulk flow in mentioned models. We assert that inflationary models with step functions which deviates from the standard model in small scales l ≤ 1Mpc can be confirmed by Large... 

Although general relativity is the underlying assumption in modern cosmology, there are still many simplifying assumptions neglecting higher order general relativistic effects. Given the precision cosmology and future surveys and the amount of data on large scales, higher order relativistic effects are to be taken into account. We will consider two categories of relativistic effects on large scale structures. First, the inhomogeneities between the source and the observer may lead to observable effects neglected so far. As future surveys will probe the universe on large scales, these effects have been the focus of recent studies. The observables being defined first, are cosmic rulers and... 

Neutrino flavor oscillations are clear evidence of massive neutrinos. It has been for more than a decade that neutrino physics became one of active topics in the field of particle physics and various experiments started studying the flavor oscillation of neutrinos. Unfortunately, experiments studying the flavor oscillations are only sensitive to the mass square difference, and they are incapable of providing more information about the absolute mass scale of neutrinos. Additionally, sterile neutrinos having non-standard interactions are under vast investigations and studies. Determination of neutrino masses and their effective number is among the most challenging problems by which... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a... 

n this thesis, the formation of cosmic structures in the presence of fuzzy dark matter (FDM) is investigated using the Gevolution code. In the FDM model, dark matter is composed of ultralight bosons. In fact, the mentioned bosons are the remnants of a scalar field present in the early universe. Simulations of structure formation in the presence of FDM that have been carried out so far (for example with Gadget and RAMSES) are based on Newtonian gravity, which have a number of limitations. The Gevolution code is an N-Body simulation that, unlike other existing simulations, is based on General Relativity, which can lead to interesting results. In fact, in this simulation, the weak field limit... 

The purpose of this research is to provide a model to explain the dependence of the galaxy distribution within voids on redshift and the density of the environment. The study of the formation of large-scale structures in the universe, as one of the most important observables in cosmology, is of great importance. Investigating the formation of these structures is possible by going beyond the linear regime and using theories such as the Press-Schechter and the excursion set. Also, by developing this type of approach, theories have been made possible to study the statistics of halos in environments such as voids, which can be useful for a better understanding of the formation and evolution of...