Jorma Louko, University of Nottingham
How long does a uniformly accelerated observer need to interact with a quantum field in order to record thermality in the Unruh temperature? In the limit of large excitation energy, the answer turns out to be
sensitive to whether (i) the switch-on and switch-off periods are stretched proportionally to the total interaction time T, or whether (ii) T grows by stretching a plateau in which the interaction remains at constant strength but keeping the switch-on and switch-off intervals of fixed duration. For a pointlike Unruh-DeWitt detector, coupled linearly to a massless scalar field in four spacetime dimensions and treated within first order perturbation theory, we show that letting T grow polynomially in the detector's energy gap E suffices in case (i) but not in case (ii), under mild technical conditions. These results limit the utility of the large E regime as a probe of thermality in time-dependent versions of the Hawking and Unruh effects, such as an observer falling into a radiating black hole. They may also have implications on the design of prospective experimental tests of the Unruh effect.
(Joint work with Christopher J Fewster and Benito A Juarez-Aubry)