Recently, the inverse β-decay rate calculated with respect to uniformly accelerated observers (experiencing the Unruh thermal bath) was revisited. Concerns have been raised regarding the compatibility of inertial and accelerated observers' results when neutrino mixing is taken into account. Here, we show that these concerns are unfounded by discussing the properties of the Unruh thermal bath with mixing neutrinos and explicitly calculating the decay rates according to both sets of observers, confirming thus that they are in agreement. The Unruh effect is perfectly valid for mixing neutrinos.

Although the Unruh effect can be rigorously considered as well tested as free quantum field theory itself, it would be nice to provide an experimental evidence of its existence. This is not easy because the linear acceleration needed to reach a temperature 1 K is of order 10 20 m/s 2 . Here, we propose a simple experiment reachable under present technology whose result may be directly interpreted in terms of the Unruh thermal bath. Instead of waiting for experimentalists to perform it, we use standard classical electrodynamics to anticipate its output and fulfill our goal.Introduction: In 1976 Unruh unveiled one of the most interesting effects of quantum field theory according to which linearly accelerated observers with proper acceleration a = constant in the Minkowski vacuum (i.e., no-particle state for inertial observers) detect a thermal bath of particles at a temperature [1] (see also note [2])

Here we discuss the description of flavor neutrinos produced or detected in processes which involve more than one neutrino. We show that in these cases flavor neutrinos cannot be separately described by pure states, but require a density matrix description. We consider explicitly the examples of νe andνµ production in µ + decay and νµ detection through scattering on electrons. We show that the density matrix which describes a flavor neutrino can be approximated with a density matrix of a pure state only when the differences of the neutrino masses are neglected in the interaction process. In this approximation, the pure states are the standard flavor states and one recovers the standard expression for the neutrino oscillation probability. We discuss also the effects of mixing of the three standard light neutrinos with heavy neutrinos which can be either decoupled because their masses are much larger than the maximum neutrino energy in the neutrino production process or because they are produced and detected incoherently. Finally, we discuss the more complicated case of neutrino-electron elastic scattering, in which the initial and final neutrinos do not have determined flavors, but there is a flavor dependence due to the different contributions of charged-current and neutral-current interactions.

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The Unruh effect is essential to keep the consistency of quantum field theory in inertial and uniformly accelerated frames. Thus, the Unruh effect must be considered as well tested as quantum field theory itself. In spite of it, it would be nice to realize an experiment whose output could be directly interpreted in terms of the Unruh effect. This is not easy because the linear acceleration needed to reach a temperature 1 K is of order 10 20 m/s 2 . We discuss here a conceptually simple experiment reachable under present technology which may accomplish this goal. The inspiration for this proposal can be traced back to Atsushi Higuchi's Ph.D. thesis, which makes it particularly suitable to pay tribute to him on occasion of his 60 th anniversary.