In the early universe, the dynamics of the Higgs field can give rise to many interesting phenomena. In the first part of this thesis, we study the behavior of the Higgs field during the reheating... Show moreIn the early universe, the dynamics of the Higgs field can give rise to many interesting phenomena. In the first part of this thesis, we study the behavior of the Higgs field during the reheating phase after cosmological inflation. We investigate the stability of the electroweak vacuum when the Higgs field is nonminimally coupled to gravity. We also study reheating in the scenario where the Higgs field itself drives inflation. In the second part, we study the possibility of generating the asymmetry between matter and antimatter during the electroweak phase transition -- the moment when the Higgs field starts to give mass to the other particles of the Standard Model. We show that it is not possible to constrain this process in a model-independent way. We also demonstrate that the predicted value of the baryon asymmetry is enhanced when leptons are included in the computation. Show less
Although the Standard Model of elementary particles successfully describes the Universe up to the smallest known scales, we know that there exists a number of observational phenomena, which do not... Show moreAlthough the Standard Model of elementary particles successfully describes the Universe up to the smallest known scales, we know that there exists a number of observational phenomena, which do not find explanation in the framework of this theory. Among these problems are Neutrino Oscillations, Dark Matter and the Baryon Asymmetry of the Universe. In this thesis, we are studying the Neutrino Minimal Standard Model (nuMSM), a minimalistic extension of the Standard Model, which can explain all these three phenomena simultaneously, by adding only three right-handed neutrinos to the known three left-handed neutrinos. It is shown that the two heavier sterile neutrinos with masses below the mass of pi-meson, could have been present in such large amounts in the early Universe that they spoil the otherwise excellent agreement between the Standard-Model prediction of light nuclei production during the Big-Bang Nucleosynthesis and the astrophysical observations. In this way, masses of sterile neutrinos are excluded from below, which reduces the potentially interesting parameter space for future accelerator searches. Another effect of sterile neutrinos in the early Universe that is studied is the production of large-scale magnetic fields due to the so-called Chiral Magnetic Effect. Show less
