  The standard wave function approach for the treatment of neutrino
oscillations fails in situations where quantum ensembles at a finite
temperature with or without an interacting background plasma are encountered.
As a first step to treat such phenomena in a novel way, we propose a unified
approach to both adiabatic and non-adiabatic two-flavor oscillations in
neutrino ensembles with finite temperature and generic (e.g. matter)
potentials. Neglecting effects of ensemble decoherence for now we study the
evolution of a neutrino ensemble governed by the associated Quantum Kinetic
Equations, which apply to systems with finite temperature. The Quantum Kinetic
Equations are solved formally using the Magnus expansion and it is shown that a
convenient choice of the quantum mechanical picture (e.g. the interaction
picture) reveals suitable parameters to characterize the physics of the
underlying system (e.g. an effective oscillation length). It is understood that
this method also provides a promising starting point for the treatment of the
more general case in which decoherence is taken into account.

High Energy Physics - Phenomenology;High Energy Physics - Theory