How at the beginning of this universe the fields as proposed in quantum fields theory get excited?? How exactly these fields originated?
Unfortunately, this question is one which is under active -- and so far fruitless -- investigation by the theoretical physics community. Anyone who could answer it would have the choice of publishing here and getting +450 reputation or so, and a couple of badges. Or they could publish in Nature of Phys Rev and get at least one Nobel Prize.
Bottom line: No one knows yet.