Executive Summary : | Neutrinos, the lightest neutral leptons, are the second most abundant particle in the universe and can come in three flavors of neutrinos: electron neutrinos, muon neutrinos, and tau neutrinos. Each type of neutrino also has an antimatter partner, called an antineutrino. The important discovery of neutrino oscillation by various solar, atmospheric, and reactor neutrino experiments revealed that neutrinos have non-zero mass and change from one flavor to another while propagating. The standard three-flavor neutrino oscillation is parametrized by three mixing angles, two mass square differences, and one Dirac CP phase. There are various current ongoing/future upcoming neutrino oscillation experiments, including T2K, DUNE, NOvA, etc., dedicated to determining unknown oscillation parameters such as (i) CP-violation in the leptonic sector and precise measurement of delta-CP phase, (ii) neutrino mass hierarchy, (iii) octant of theta-23 etc. The violation of charge-conjugation and parity reversal (CP) symmetry can be measured if the oscillations of neutrinos are fundamentally different from the oscillations of antineutrinos. The study of CP-violation is a topic of fundamental importance in particle physics and is intimately connected to the matter-antimatter asymmetry of the universe. The goal of the project is to study theoretically the effects of neutrino decay and decoherence in neutrino oscillation for estimation of CP-violation using various analytic approximation such as OMSD, alpha-s13 and perturbation series methods. These effects will provide the important contributions to the neutrino oscillation probabilities and will affect the precise measurement of unknown neutrino parameters like mass-hierarchy, octant sensitivity. The neutrino decay can be incorporated in the Hamiltonian in the well known Schrodinger wave equation describes the time evolution of the neutrino states. However, the neutrino decay term destroys the hermicity of the Hamiltonian. Therefore, we will utilize mathematical techniques like Baker-Campbell-Hausdorff (BCH) formula to find the eigenvalues and neutrino oscillation probabilities, including decay effects. The importance of the study lies in the fact that the invisible decay of neutrinos to final states can probe the nature of neutrinos to be Dirac or Majorana, depending upon the mode of decay. The role of decoherence effects in neutrino oscillation and anayltic estimation of their sensitivity to CP-violation can be studied using density matrix formalism (Von Neumann equation) and by the Lindblad master equation. The study of CP-violation in neutrino oscillation is one of the important science goal of current and future planned neutrino oscillation experiments, such as T2K, DUNE, NOvA. The analytic understanding of CP-violation in neutrino oscillation including decay and decoherence effects using various adopted approximations considered in the current proposal will be complementary study to these experiments. |