Transition probabilities of atomic systems between moving walls

The transition probabilities of a quantum system introduced between parallel conducting walls approaching or receding from each other with arbitrary constant relative speed are evaluated in the dipole approximation. The interaction with the vacuum fluctuations of the quantum electromagnetic field inside the box induces modifications in the spontaneous emission probabilities. While the transition probabilities in free space are recovered in the ultrarelativistic limit, and enhancement or inhibition of the spontaneous emission in the non-relativistic limit is expected according to the dipole moment orientation of the detector. These results are discussed in the context of photon generation by the moving walls.