W. Zimdahl et al., COLLISIONAL EQUILIBRIUM, PARTICLE-PRODUCTION, AND THE INFLATIONARY UNIVERSE, Physical review. D. Particles and fields, 54(10), 1996, pp. 6101-6110
Particle production processes in the expanding universe are described
within a simple kinetic model. The equilibrium conditions for a Maxwel
l-Boltzmann gas with variable particle number are investigated. We fin
d that radiation and nonrelativistic matter may be in equilibrium at t
he same temperature provided the matter particles are created at a rat
e that is half the expansion rate. Using the fact that the creation of
particles is dynamically equivalent to a nonvanishing bulk pressure w
e calculate the back reaction of this process on the cosmological dyna
mics. It turns out that the 'adiabatic' creation of massive particles
with an equilibrium distribution for the latter necessarily implies po
wer-law inflation. Exponential inflation in this context is shown to b
ecome inconsistent with the second law of thermodynamics after a time
interval of the order of the Hubble time.