  This thesis is devoted to the development of a nonperturbative quantum field
theoretical approach to flavour physics, with special attention to cosmological
applications. Neutrino flavour oscillation is nowadays a fairly
well-established experimental fact. However, the formulation of flavour
oscillations in a relativistic field theoretical framework presents non-trivial
difficulties. A nonperturbative approach for building flavour states has been
proposed by Blasone, Vitiello and coworkers. The formalism implies a
non-trivial physical vacuum (called "flavour vacuum"), which might act as a
source of Dark Energy. Furthermore, such a vacuum has been recognized as the
effective vacuum state arising in the low energy limit of a string theoretical
model, D-particle Foam Model. In the attempt of probing the observable
phenomenology of the D-particle foam model, a simple toy model (two scalars
with mixing \`a la Blasone & Vitiello on a adiabatically expanding background)
has been studied, proving that the flavour vacuum might behave as Dark Energy
under certain assumptions. The first work presented in this thesis represents a
development of this approach. A more realistic model is considered, which
includes two flavoured Dirac fermions on a generic Friedmann-Robertson-Walker
universe. In this framework we show that the flavour vacuum presents different
features, which are incompatible with Dark Energy. Motivated by this
discrepancy, we next embark on the analysis of a simple supersymmetric model in
flat spacetime (free Wess-Zumino), proving that the bosonic component of
flavour vacuum acts as Dark Energy, whereas the fermionic as a source of Dark
Matter. Finally we develop a new method of calculation that open the way to a
nonperturbative extension of these results for interactive theories.
