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... 

We know the matter can curve the space-time according to the general theory of relativity. On the other hand Quantum Field Theory has been formulated in a flat space-time and we cannot use most of its techniques within a curved space-time. Formulating the Quantum Field Theory in curved space-time is important for various subjects in physics like early universe or black hole physics. We will review the formulating QFT in cosmological background and will look for observable consequences on Cosmological Microwave Background in this thesis  

In the second half of the 20th century, the standard cosmology was encountered some problems like flatness problem and horizon problem. The inflation theory proposed by Alan Guth in the 1980s, not only solved these problems but also predicted some primordial fulctuations for the universe that as a source for the fluctuations of cosmic microwave background, could explain our observations.The fluctuations predicted by simple inflationary models, are Gaussain. Although we have not found a valid observational result suggesting Non-Gaussianity in the primordial fluctuations so far, but these simple single scalar field inflationary models, are very specific. So it is very probable that in the... 

Temerature fluctuation of the Cosmic Microwave Background (CMB) is one of the key observebles of the modern cosmology. Today, it is widely believed that quantum fluctuation that are stretched to horizon scales during a period of acceleration expansion -- at the onset of evolution of the universe-- are responsible for these perturbations. In the simplest scenarios of the inflation, a scalar field is responsible for both nearly expansional expansion of the universe and the proimordial fluctuations. In this thesis, we investigate the models of inflation with an additional light degree of freedom. In particular, we employ the method of the Effective Field Theory to study the general structure...