W. Zimdahl et Ab. Balakin, INFLATION IN A SELF-INTERACTING GAS UNIVERSE - ART. NO. 063503, Physical review. D. Particles and fields, 5806(6), 1998, pp. 3503
We show that de Sitter spacetime is a solution of Einstein's field equ
ations with the energy momentum tensor of a self-interacting, classica
l Maxwell-Boltzmann gas in collisional equilibrium. The self-interacti
on is described by a four-force which is quadratic in the (spatially p
rojected) particle four-moments. This force does not preserve the part
icle number and gives rise to an exponential increase in the comoving
entropy of the universe while the temperature of the latter remains co
nstant. These properties of a gas universe are related to the existenc
e of a ''projector-conformal'' timelike Killing vector representing a
symmetry which is in between the symmetries characterized by a Killing
vector and those characterized by a conformal Killing vector. [S0556-
2821(98)07016-7].