We study the interplay between coherence and mixedness in meson and neutrino systems. The dynamics of the meson system is treated using the open quantum system approach taking into account the decaying nature of the system. Neutrino dynamics is studied in the context of three flavor oscillations within the framework of a decoherence model recently used in the context of LSND (Liquid Scintillator Neutrino Detector) experiment. For meson systems, the decoherence effect is negligible in the limit of zero CP violation. Interestingly, the average mixedness increases with time for about one lifetime of these particles. For neutrino system, in the context of the model considered, the decoherence effect is maximum for neutrino energy around 30 MeV. Further, the effect of CP violating phase is found to decrease (increase) the coherence in the upper 0 < δ < π (lower π < δ < 2π) half plane.

Many facets of nonclassicality are probed in the context of three flavour neutrino oscillations including matter effects and CP violation. The analysis is carried out for parameters relevant to two ongoing experiments NOνA and T2K, and also for the upcoming experiment DUNE. The various quantum correlations turn out to be sensitive to the masshierarchy problem in neutrinos. This sensitivity is found to be more prominent in DUNE experiment as compared to NOνA and T2K experiments. This can be attributed to the large baseline and high energy of the DUNE experiment. Further, we find that to probe these correlations, the neutrino (antineutrino) beam should be preferred if the sign of mass square difference Δ 31 turns out to be positive (negative).

Gravity induced neutrino-antineutrino oscillations are studied in the context of one and two flavor scenarios. This allows one to investigate the particle-antiparticle correlations in two and four level systems, respectively. Flavor entropy is used to probe the entanglement in the system. The well known witnesses of non-classicality such as Mermin and Svetlichly inequalities are investigated. Since the extent of neutrino-antineutrino oscillation is governed by the strength of the gravitational field, the behavior of non-classicality shows interesting features as one varies the strength of the gravitational field. Specifically, the suppression of the entanglement with the increase of the gravitational field is observed which is witnessed in the form of decrease in the flavor entropy of the system. The features of the Mermin and the Svetlichny inequalities allow one to make statements about the degeneracy of neutrino mass eigenstates.

29182 stars observed at mountain altitudes in Kenya are analysed statistically. The analysis gives: -(1) An absorption thickness of 149 g/cm 2 near the geomagnetic equator.(2) The star frequency as a function of the total number of prongs in a star is the result of the composition of the emulsion. (3) The empirical formula of T euch er for the energy of the star producing particle can be used in our experiments. (4) The variation in the number of shower particles with the complexity of the star and the altitude appears to be in agreement with the Heisenberg theory of the plural production of mesons.

We study the geometric phase for neutrinos at various man-made facilities, such as the reactor and accelerator neutrino experiments. The analysis is done for the three flavor neutrino scenario, in the presence of matter and for general, noncyclic paths. The geometric phase is seen to be sensitive to the CP violating phase in the leptonic sector and the sign ambiguity in ∆31. We find that for neutrino experimental facilities where the geometric phase can complete one cycle, all the phase curves corresponding to different values of CP violating phase, converge to a single point, called the cluster point. There are two distinct cluster points for positive and negative signs of ∆31. Thus the geometric phase can contribute to our understanding of the neutrino mass hierarchy problem.