FRW Cosmologies with Adiabatic Matter Creation

Some properties of cosmological models with matter creation are investigated in the framework of the Friedman-Robertson-Walker (FRW) line element. For adiabatic matter creation, as developed by Prigogine and coworkers, we derive a simple expression relating the particle number density $n$ and energy density $\rho$ which holds regardless of the matter creation rate. The conditions to generate inflation are discussed and by considering the natural phenomenological matter creation rate $\psi =3 \beta nH$, where $\beta$ is a pure number of the order of unity and $H$ is the Hubble parameter, a minimally modified hot big-bang model is proposed. The dynamic properties of such models can be deduced from the standard ones simply by replacing the adiabatic index $\gamma$ of the equation of state by an effective parameter $\gamma_{*} = \gamma (1 - \beta)$. The thermodynamic behavior is determined and it is also shown that ages large enough to agree with observations are obtained even given the high values of $H$ suggested by recent measurements.