Conformal anomalies and massless particle generation in a Fridman universe

The general structure of conformai anomalies of the energy-momentum tensor is established. The energy density of massless particles generated during the cosmological expansion is calculated in the lowest-order perturbation theory. Estimates are made that indicate that the energy density of generated massless particles in the early universe can significantly exceed the energy density of the generated massive particles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 54–58, August, 1984.We are grateful to E. S. Fradkin, V. P. Frolov, I. V. Tyutin, and B. L. Voronov for useful discussions.