Acceleration of quantum fields

We analyze the transformation of quantum fields under conformal coordinate transformations from inertial to accelerated frames, in the simple case of scalar massless fields in a two-dimensional spacetime, through the transformation of particle number and its spectral density. Particle number is found to be invariant under conformal coordinate transformations to uniformly accelerated frames, which extends the property already known for vacuum. Transformation of spectral density of particle number exhibits a redistribution of particles in the frequency spectrum. This redistribution is determined by derivatives of phase operators with respect to frequency, that is by time and position operators defined in such a manner that the redistribution of particles appears as a Doppler shift which depends on position in spacetime, in conformity with Einstein equivalence principle. PACS numbers: 12.20 Ds 03.70 42.50 Lc LPTENS 95/30 to appear in Brazilian Journal of Physics, special issue on Quantum Optics, ed. L. Davidovich. Unité propre du Centre National de la Recherche Scientifique, associée à l’Ecole Normale Supérieure et à l’Université de Paris Sud. Unité de l’Ecole Normale Supérieure et de l’Université Pierre et Marie Curie, associée au Centre National de la Recherche Scientifique.