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.
