Key points are not available for this paper at this time.
The production of particles by gravitational fields is calculated within the framework of quantum field theory. It turns out that the expansion of the universe---giving rise to a time-dependent gravitational field---does not lead to an appreciable production at present, since the frequencies involved are too low. Particle production was, however, of importance during the first 10^-20 sec after a "big bang. " This mechanism of particle creation leads to equal numbers of particles and antiparticles.
Sexl et al. (Tue,) studied this question.