Primordial Non-Gaussianity as a Probe of High Energy Physics

The inflationary scenario is the well-established cosmological model which provides the initial states of our universe. It might be one of the highest energy ( 1014 GeV) phenomenon we can observe. It is a natural idea to pioneer the high energy frontier with cosmic inflation. In the first part of the thesis, we introduce the holographic approach to inflation. Inflation is also an ideal avenue to study quantum gravity via the holographic principle. Holography states that gravity in the bulk should be fully encoded by a quantum field theory on the boundary. The inflationary universe is described by a quasi de Sitter space, and there may exist a corresponding deformed conformal field theory on the boundary. The time evolution history of inflation corresponds to the renormalization group flow on the boundary quantum field theory. We implement the holographic principle to study the symmetry perspective of the CMB. We used the holographic principle to the general single field inflation and studied its dual quantum field theory. In the second part of the thesis, we explore the imprints of massive fields on the primordial non-Gaussianities, so called cosmological collider physics. We study the regime where the inflaton is strongly coupled to massive fields, its power spectrum and non-Gaussianities. Then we study the scenario where our universe starts from an initial state with finite temperature, the imprints of the heavy particles will not be as small as people usually expected. We have also shown the smoking gun of phase transition during inflation. We also introduce the interplay between scattering amplitudes and cosmology.