INFLATION IN A SELF-INTERACTING GAS UNIVERSE - ART. NO. 063503

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].