Neutrinos And Quantum Fields In The Universe

The first part of this work focuses on the information that neutrinos from core-collapse supernovae (CCSNe) can provide with in the context of multi-messenger astronomy. A CCSN serves as nature’s very own laboratory. Neutrinos from the various phases of a CCSN can be used to gain insights and understanding in a much broader context. The localization of a star using presupernova neutrinos is studied and it is shown that their topology can give the direction to the star with an error of ~ 60 degrees. A new phenomenological description of the neutrino gravitational wave memory effect is built, highlighting its detectability, and physics potential in the present context. It is shown that this effect will be detectable in the near future, for a galactic supernova, at deci-Hertz GW interferometers. A novel idea of how observations of the neutrino GW memory from CCSNe will enable time-triggered searches of supernova neutrinos at megaton (Mt) scale neutrino detectors is also presented. This combination of a deci-Hz GW and a Mt-neutrino detector will allow the latter to detect ~ 3 - 30 supernova neutrino events/Mt/per decade of operation.The second part of this work focuses on studying quantum fields in time and space- dependent backgrounds. Generically, such quantum fields get excited (a phenomenon known as particle production) and the quantum excitations then backreact on the background. This scenario is important in all areas of physics, specifically in the context of gravitation and cosmology. This work discusses some simplified models pertaining to this. In particular, the dynamics of a classical field rolling down a linear potential while it is bi-quadratically coupled to a quantum field is studied. The formation of global topological defects in d-dimensions as a result of spontaneous symmetry breaking during a quantum phase transition is also studied. Furthermore, a sine-Gordon kink-antikink collision in the presence of interactions with a scalar field is considered and the regimes of breather and long lived oscillon formation are found.