Two-fluid solutions of particle-creation cosmologies

Cosmological evolution driven incorporating continuous particle creation by the time-varying gravitational field is investigated. We consider a spatially flat, homogeneous and isotropic universe with two matter fluids in the context of general relativity. One fluid is endowed with gravitationally induced `adiabatic' particle creation, while the second fluid simply satisfies the conservation of energy. We show that the dynamics of the two fluids is entirely controlled by a single nonlinear differential equation involving the particle creation rate, $\Gamma (t)$. We consider a very general particle creation rate, $\Gamma (t)$, that reduces to several special cases of cosmological interest, including $\Gamma =$ constant, $% \Gamma \propto 1/H^{n}$ ($n\in \mathbb{N}$), $\Gamma \propto \exp (1/H)$. Finally, we present singular algebraic solutions of the gravitational field equations for the two-fluid particle creation models and discuss their stability.