On the Cancellation Mechanism of Radiation from the Unruh detector

摘要

A uniformly accelerated detector (Unruh detector) in the Minkowski vacuum isexcited as if it is exposed to the thermal bath with temperature proportionalto its acceleration. In the inertial frame, since both of an excitation and adeexcitation of the detector are accompanied by emission of radiation into theMinkowski vacuum, one may suspect that the Unruh detector emits radiation likethe Larmor radiation from an accelerated charged particle. However, it is knownthat the radiation is miraculously cancelled by a quantum interference effect.In this paper, we investigate under what condition the radiation cancels out.We first show that the cancellation occurs if the Green function satisfies arelation similar to the Kubo-Martin-Schwinger (KMS) condition. We then studytwo examples, Unruh detectors in the 3+1 dimensional Minkowski spacetime and inthe de Sitter spacetime. In both cases, the relation holds only in a restrictedregion of the spacetime, but the radiation is cancelled in the whole spacetime.Hence the KMS-like relation is necessary but not sufficient for thecancellation to occur.