  Mixing transformations for a uniformly accelerated observer (Rindler
observer) are analyzed within the quantum field theory framework as a basis for
investigating gravitational effects on flavor oscillations. In particular, the
case of two charged boson fields with different masses is discussed. In spite
of such a minimal setting, the standard Unruh radiation is found to loose its
characteristic thermal interpretation due to the interplay between the
Bogolubov transformation hiding in field mixing and the one arising from the
Rindler spacetime structure. The modified spectrum detected by the Rindler
observer is explicitly calculated in the limit of small mass difference.
