Particle creation in the early Universe: achievements and problems
  Results on particle creation from vacuum by the gravitational field of the expanding Friedmann Universe are presented. Finite results for the density of particles and the energy density for created particles are given for different exact solutions for different regimes of the expansion of the Universe. The results are obtained as for conformal as for nonconformal particles. The hypothesis of the origination of visible matter from the decay of created from vacuum superheavy particles identified with the dark matter is discussed. 
A. A. Grib, Yu. V. Pavlov
gr-qc