RT Journal Article T1 Particle production from nonlocal gravitational effective action A1 Dobado González, Antonio A1 López Maroto, Antonio AB In this paper we show how the nonlocal effective action for gravity, obtained after integrating out the matter fields, can be used to compute particle production and spectra for different space-time metrics. Applying this technique 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-Walker space-time. Using an adiabatic approximation we also obtain the corresponding spectra and compare the results with the traditional WKB approximation. [S0556-2821(99)02920-3]. PB American Physical Society SN 0556-2821 YR 1999 FD 1999-11-15 LK https://hdl.handle.net/20.500.14352/58720 UL https://hdl.handle.net/20.500.14352/58720 LA eng NO ©1999 The American Physical Society.A.L.M acknowledges support from SEUID-Royal Society. This work has been partially supported by Ministerio de Educación y Ciencia (Spain) CICYT (AEN96-1634). NO Ministerio de Educación y Ciencia (Spain) NO CICYT DS Docta Complutense RD 8 jun 2025