Particle production from nonlocal gravitational effective action - art. no. 104045

In this paper we show how the nonlocal effective action for gravity, obtain ed after integrating out the matter fields, can be used to compute particle production and spectra for different space-time metrics. Applying this tec hnique to several examples, we End that the perturbative calculation of the effective action up to second order in curvatures yields exactly the same results for the total number of particles as the Bogolyubov transformations method, in the case of massless scaler fields propagating in a Robertson-W alker space-time. Using an adiabatic approximation we also obtain the corre sponding spectra and compare the results with the traditional WKB approxima tion. [S0556-2821(99)02920-3].