LOSS OF QUANTUM COHERENCE THROUGH SCATTERING OFF VIRTUAL BLACK-HOLES

In quantum gravity, fields may lose quantum coherence by scattering of f vacuum fluctuations in which virtual black hole pairs appear and dis appear. Although it is not possible to properly compute the scattering off such fluctuations, we argue that one can get useful qualitative r esults, which provide a guide to the possible effects of such scatteri ng, by considering a quantum field on the C metric. which has the same topology as a virtual black hole pair. We study a scalar field on the Lorentzian C metric background, with the scalar field in the analytic ally continued Euclidean vacuum state. We find that there are a finite number of particles at infinity in this state, contrary to recent cla ims made by Yi. Thus, this state is not determined by data at infinity , and there is loss of quantum coherence in this semiclassical calcula tion. [S0556-2821(97)01022-9].