ar X iv : g r - qc / 9 90 50 41 v 1 1 3 M ay 1 99 9 Particle creation , renormalizability conditions and the mass - energy spectrum in gravity theories of quadratic

Massive scalar particle production, due to the anisotropic evolution of a five-dimensional spacetime, is considered in the context of a quadratic Lagrangian theory of gravity. Those particles, corresponding to field modes with non-vanishing momentum component along the fifth dimension, are created mostly in the neighbourhood of a singular epoch where only their high-frequency behaviour is of considerable importance. At the one-loop approximation level, general renormalizability conditions on the physical quantities relevant to particle production are derived and discussed. Exact solutions of the resulting Klein-Gordon field equation are obtained and the mass-energy spectrum, attributed to the scalar field due to the cosmological evolution, is being further investigated. Finally, analytic expressions regarding the number and the energy density of the created particles at late times, are also derived and discussed.